Bacteria PDF

In most bacteria, growth involves: -increase in cell mass and number of ribosomes, - duplication of the bacterial chromosome, -synthesis of new cell wall and plasma membrane, -partitioning of the two chromosomes, septum formation, and cell division. This asexual process of reproduction is called bin...

In most bacteria, growth involves: -increase in cell mass and number of ribosomes, - duplication of the bacterial chromosome, -synthesis of new cell wall and plasma membrane, -partitioning of the two chromosomes, septum formation, and cell division. This asexual process of reproduction is called binary fission. Optimal growth temperature • Mesophiles: – human body temperature * pathogens * opportunists • Psychrophile – close to freezing • Thermophile – close to boiling. Psychrophiles: Common in the oceanic environments of Arctic and Antarctica. They live at temperatures between -5 ° and 20 ° and their optimum is a temperature lower than 15°. Optional psychrophiles: they are able to live in cold environments but also in mild environments and are the micro-organisms responsible for the deterioration of chilled foods. They live at temperatures between 0 ° and 35 ° and their optimum temperature is less than 20 °. Mesophiles: they live in environments with average temperatures ranging from 10 ° to 50 °, with an optimum between 20 ° and 40 °. Most microorganisms, including human pathogens, are mesophilic bacteria. Thermophiles: they live at high temperatures between 45 ° and 80 ° and are the bacteria that live in soils or waters associated with volcanic activities or exposed directly to the sun. Hyperthermophiles: they live at temperatures between 80 ° and 115 °, prohibitive for all other living beings. They are bacteria that live in close proximity to fumaroles of ocean depths from which sulfur-rich waters reach temperatures of hundreds of degrees centigrade. Many bacteria grow best at neutral pH Some can survive/grow: - acid – alkali. Protein synthesis is the target of different Antibiotic classes: Aminoglycosides (streptomicina, gentamicina) = bind the proteins in 30S ribosome Tetracyclines = interfere with the elongation phase in 30S ribosome Macrolides (erythromycin) interfere with the elongation phase in 50S ribosome. Generation time • Time necessary to the duplication of a bacterial cell. Some pathogens can begin an infection with only a small number of cells in the initial inoculum. For example, enterohemorrhagic strains of Escherichia coli require an infective dose of only about ten cells. By contrast, other pathogens, such as Vibrio cholerae, require a large number of cells (103 to 108 cells) in the inoculum to successfully infect a host. Antibiotic: substance produced by a microorganism that kills or inhibits the growth of another microorganism • Antimicrobial agent: Chemical (natural or synthetic) that kills or inhibits the growth of microorganisms. Consequences of Antibiotics….. Antibiotic treatment can rapidly alter the most common microbes that colonize the gastrointestinal tract, causing the proliferation of antibiotic-resistant organisms, such as Enterococcus, Pseudomonas, and fungi. C. difficile can also grow rapidly in this situation, leading to diseases ranging from diarrhea to pseudomembranous colitis.. Principles and Definitions • Antibiotic susceptibility testing (in vitro) – Minimum inhibitory concentration (MIC) • Lowest concentration that results in inhibition of visible growth – Minimum bactericidal concentration (MBC) • Lowest concentration that kills 99.9% of the original inoculum. The principal mechanisms of resistance to antibacterial drugs are: 1. prevention of penetration of drug, alteration and interference in conveying the drug 2. activation of efflux pumps, rapid ejection of the drug 3. modification of the target site of antibiotic 4. enzymatic drug destruction or inactivation 5. Modulation of the genic expression to produce a greater number of target sites (competition with substrate). Resistance to antiviral drugs The (in)ability of the virus to replicate in the presence of antiretroviral drugs Caused by changes in relevant part of the virus genome (mutations) What Factors Promote Antimicrobial Resistance? • Exposure to sub-optimal levels of antimicrobial • Exposure to microbes carrying resistance genes. Inappropriate Antimicrobial Use • Prescription not taken correctly • Antibiotics for viral infections • Antibiotics sold without medical supervision • Spread of resistant microbes in hospitals due to lack of hygiene. • Lack of quality control in manufacture or outdated antimicrobial • Inadequate surveillance or defective susceptibility assays • Poverty or war • Abuse of antibiotics in animals and foods. • Combination therapy – Prevent emergence of resistant strains – Temporary treatment until diagnosis is made – Antibiotic synergism • Penicillins and aminoglycosides • CAUTION: Antibiotic antagonism –Penicillins and bacteriostatic antibiotics. beta-lactam antibiotics Penicillins Cephalosporins Cephamycins Carbapenemics Monobactams Beta-lactamase inhibitors (clavulanic acid). • Penicillins are active against most grampositive bacteria such as staphylococci and streptococci , against the spirochete (Treponema pallidum and Leptospira ) , against gonococci and meningococci. • Despite penicillins are bactericidal antibiotics, due to heavy use that is being made and the production of enzymes (penicillinases or β - lactamase) by bacteria, often we observe bacterial resistance phenomena. Semisynthetic Penicillins: • Penicilinase-resistant penicillins • Carbapenems: very broad spectrum • Monobactam: Gram negative • Extended-spectrum penicillins • Penicillins + b-lactamase inhibitors Cephalosporins and Cephamycins: The cephalosporins are β-lactam antibiotics derived from 7 aminocephalosporanic acid (the βlactam ring is fused with a dihydrothiazine ring) that was originally isolated from the mold Cephalosporium. First and second generation active against gram-positive and some gram-negative (Narrow Spectrum) Third generation active against grampositive and increased activity against gram-negative (Expanded spectrum) The cephamycins are closely related to the cephalosporins, except that they contain oxygen in place of sulfur in the dihydrothiazine ring, rendering them more stable to β-lactamase hydrolysis. Carbapenems: The Carbapenems are very broad bacterial spectrum, the broader found between beta- lactams antibiotics. Characterized by: a rapid bactericidal action due to a faster crossing of porins D2 of the bacterial wall a great hydrolytic stability to the action made by almost all the betalactamase plasmidic and chromosomic. PBP are targets for penicillin and other betalactam antibiotics Bacteria penicillin-resistant change. PBP structure Peptidoglycan: is a complex polymer made of polysaccharide linear chains consisting of crosslinked NAM: Nacetylmuramic acid and NAG: N-acetylglucosamine. These bonds are catalyzed by transpeptidase, transglycosidase, endopeptidase and carbossipeptidase bond to the membrane. These enzymes are called penicillin-binding proteins (PBPs) because they are targets for penicillin and other beta-lactam antibiotics. Bacteria can become resistant to β-lactam antibiotics by three general mechanisms: 1) prevention of the interaction between the antibiotic and the target PBP (seen in gramnegative bacteria, particularly Pseudomonas species). 2) modification of the binding of the antibiotic to the PBP 3) hydrolysis of the antibiotic by bacterial enzymes, β-lactamases. Mechanisms of resistance to beta-lactam antibiotics: • mutations in the PBPs. These mutations do not allow the binding with the antibiotic • production of beta-lactamase that disrupts the beta-lactam ring of the antibiotic • no entrance through the outer membrane (only for gram-negative). Bacteria can produce βlactamases that inactivate the β-lactam antibiotics. The β-lactamases are in the same family of serine proteases as the PBPs. >200 different β-lactamases have been described. Some are specific for penicillins (i.e., penicillinases), cephalosporins (i.e., cephalosporinases), or carbapenems (i.e., carbapenemases), whereas others have a broad range of activity, including some that are capable of inactivating most β-lactam antibiotics. BETA-LACTAMASE INHIBITORS: Clavulanic acid, Sulbactam • These molecules are combined with Penicillins (ampicillin, amoxicillin, piperacillin) to treat bacteria that produce beta-lactamase. • These inhibitors bind and inactivate beta-lactamase and allow Penicillins to enter the bacteral cell without undergoing enzymatic degradation. Vancomycin: glycopeptide antibiotic used in the prophylaxis and treatment of infections caused by Gram-positive bacteria. It acts by inhibiting proper cell wall synthesis in Grampositive bacteria. • It interacts with D-alanine D-alanine terminal of lateral pentapeptidic chains interfering with the formation of bridges • Resistant bacteria replace the D-alanine with Dlactate that does not bind the antibiotic. •Active against oxacillin-resistant staphylococci and other grampositives resistant to beta-lactamase. • Inactive on gramnegatives: big molecule can not enter the outer membrane of gram-negatives.. • Mode of action - The aminoglycosides irreversibly bind to the 16S ribosomal RNA and freeze the 30S initiation complex (30SmRNA-tRNA) so that no further initiation can occur. They also slow down protein synthesis that has already initiated and induce misreading of the mRNA. May also destabilize bacterial membranes. • Spectrum of Activity -Many gram-negative and some grampositive bacteria; Not useful for anaerobic (oxygen required for uptake of antibiotic) or intracellular bacteria. • Resistance - Common • Synergy - The aminoglycosides synergize with beta-lactam antibiotics. The beta-lactams inhibit cell wall synthesis and thereby increase the permeability of the aminoglycosides. • Aminoglycosides are the first choice for infections caused by gram negative bacilli. Three Mechanisms of Resistance: • Mutations in the binding site to the ribosome • Decreased penetration in bacterial cell • Enzymatic modification of the antibiotic by phosphorylation, adenylation or acetylation of aminic and hydroxylic groups. Spectinomycin (bacteriostatic) • Mode of action - Spectinomycin reversibly interferes with m-RNA interaction with the 30S ribosome. It is structurally similar to the aminoglycosides but does not cause misreading of mRNA. • Spectrum of activity - Used in the treatment of penicillin-resistant Neisseria gonorrhoeae • Resistance - Rare in Neisseria gonorrhoeae. Tetracyclines (bacteriostatic) tetracycline, minocycline and doxycycline • Mode of action - The tetracyclines reversibly bind to the 30S ribosome and inhibit binding of aminoacyl-t-RNA to the acceptor site on the 70S ribosome. • Spectrum of activity - Broad-spectrum against gram positive and some gram negative bacteria. Useful against intracellular bacteria • Resistance - Common • Adverse effects - Destruction of normal intestinal flora resulting in increased secondary infections; staining and impairment of the structure of bone and teeth. Chloramphenicol • Broad-spectrum, but it is used only in the treatment of typhoid fever or for bacterial meningitis, for its bone marrow toxicity. It can cause aplastic anemia • It has a bacteriostatic effect . It binds the 50S ribosome and blocks the peptide extension. • Resistance is common, it is mediated by an acetylation reaction. The oxydrilic group of the antibiotic molecule is acetylated and this inhibits the antibiotic. Macrolides (bacteriostatic) erythromycin, clarithromycin, azithromycin, spiramycin • Mode of action - The macrolides inhibit translocation. • Spectrum of activity - Broad-spectrum, active against gram positive and some gram negative bacteria (neisseria, legionella, treponema, mycoplasma, chlamydia) • Resistance – Common Fusidic acid (bacteriostatic) • Mode of action - Fusidic acid binds to elongation factor G (EF-G) and inhibits release of EF-G from the EF-G/GDP complex. • Spectrum of activity - Gram-positive cocci. Rifampin, Rifamycin, Rifampicin, Rifabutin (bactericidal) • Mode of action These antimicrobials bind to DNAdependent RNA polymerase and inhibit initiation of mRNA synthesis. • Spectrum of activity - Wide spectrum but is used most commonly in the treatment of tuberculosis • Resistance - Common • Combination therapy - Since resistance is common, rifampin is usually used in combination therapy • Rifampicin inhibits DNA-dependent RNA poymerase which leads to suppression of RNA synthesis in susceptible bacteria. Thus it inhibits transcription process. • The site of action appears to be the ß subunit of the enzyme. • Rifampicin may be bacteriostatic or bactericidal, depending on the concentration of the drug and the relative susceptibility of the organism. Rifampicin is most effective when cell division is occurring. • This drug is generally used against Mycobacterium tuberculosis. Resistance to Rifampicin • Modification of the beta-subunit of RNA polymerase. This modification does not allow binding with the drug. • Gram negative are naturally resistant because hydrophobic antibiotic do not cross the external wall. Quinolones (bactericidal) nalidixic acid, ciprofloxacin, ofloxacin, norfloxacin, levofloxacin, lomefloxacin, sparfloxacin: • Mode of action - These antimicrobials bind to the A subunit of DNA gyrase - topoisomerase and prevent supercoiling of DNA, thereby inhibiting DNA synthesis. • Spectrum of activity Gram-positive cocci and urinary tract infections • Resistance - Common for nalidixic acid; developing for ciprofloxacin. • Quinolones can be divided in: - Narrow-spectrum (ac. Nalidixic): Active against gramnegative bacilli, not gram-positive - Broad-spectrum (ciprofloxacin, norfloxacin, ofloxacin) active against gram-positive and gramnegative bacteria. Resistance to chinolones is mediated by: - Decreased drug entry into bacterial cell due to alteration of membrane porin - Modification of DNA gyrase that can not bind the drug anymore. Antimetabolite antimicrobials: Sulfamidics • Effective against to great number of gram-positive and gram-negative • Elective drugs for the treatment of acute infections of urinary tract caused by susceptible bacteria like E. coli. • They inhibit the synthesis of folic acid. • Sulfonamide binds the enzyme involved in the acid folic synthesis in place of the natural substrate (the p - amino benzoic acid, PABA) Sulfonamides, Sulfones (bacteriostatic) • Mode of action - These antimicrobials are analogues of para-aminobenzoic acid and competitively inhibit formation of dihydropteroic acid. • Spectrum of activity - Broad range activity against grampositive and gram-negative bacteria; used primarily in urinary tract and Nocardia infections. • Resistance - Common • Combination therapy - The sulfonamides are used in combination with trimethoprim; this combination blocks two distinct steps in folic acid metabolism and prevents the emergence of resistant strains. Resistance to sulphamidics • Resistant bacteria have an alternative enzyme for folic acid synthesis encoded by a plasmid • Iperproduction of the natural substrat (PABA) Trimethoprim, Methotrexate, Pyrimethamine (bacteriostatic) • Mode of action These antimicrobials binds to dihydrofolate reductase and inhibit formation of tetrahydrofolic acid. • Spectrum of activity - Broad range activity against grampositive and gram-negative bacteria; used primarily in urinary tract and Nocardia infections. • Resistance - Common • Combination therapy - These antimicrobials are used in combination with the sulfonamides; this combination blocks two distinct steps in folic acid metabolism and prevents the emergence of resistant strains. MRSA “ mer-sah” • Methicillin-Resistant Staphylococcus aureus • Most frequent nosocomial (hospital-acquired) pathogen • Usually resistant to several other antibiotics. Proposals to Combat Antimicrobial Resistance • Use more narrow spectrum antibiotics • Use antimicrobial cocktails GENERAL BACTERIOLOGY The smallest bacteria (Chlamydia and Rickettsia) are just 0.1 to 0.2 μm in diameter, whereas larger bacteria may be many microns in length. Thiomargarita namibiensis is world’s largest bacteria, a gramnegative Proteobacterium found in the ocean sediments of the coast of Namibia. Usually it is 100—300 µm across, but bigger cells have been observed up to 0.75 mm (750 µm). Bacteria can be classified by their macroscopic and microscopic appearance, by characteristic growth and metabolic properties, by their antigenicity, and finally by their genotype. The initial distinction between bacteria can be made by growth characteristics on different nutrient and selective media. The bacteria grow in colonies, with specific characteristics, such as color, size, shape, and smell. The ability to resist certain antibiotics, ferment specific sugars (e.g., lactose, to distinguish E. coli from Salmonella) or to lyse erythrocytes (hemolytic properties) can also be determined using the appropriate growth media. BACTERIA Shape Spherical (cocci) Cylindrical/rodshaped (bacilli) Bend (vibrions, spirilla, spirochetes) Spherical (cocci): Streptococcus pneumoniae Staphylococcus aureus Neisseria gonorrhoeae Neisseria meningitidis. Cylindrical/rod-shaped (bacilli): Enterobacteriaceae: Escherichia coli, Salmonella, Shigella. Yersinia pestis Legionella pneumophilae, Haemophilus influenzae, Clostridium tetani, Clostridium botulinum e ,Clostridium perfrigens ,Bacillus anthracis, Mycobacterium tuberculosis, M. leprae, M. bovis e M. avium complex. Spiral form, Bend (vibrions, spirilla, spirochetes] Cell membrane: sterols[cholesterol] are absent and replaced by terpenoids with the same function of stabilizing and compacting. Specific organelles are absent, it is the site of electrons transport and energy production (no mitochondria) and contains transport proteins, ion pumps and enzymes. The Mesosome is a portion of the cytoplasmic membrane invaginations and the site for the anchorage and duplication of the bacterial DNA Cell wall of gram+ bacteria The cell wall is composed by peptidoglycan. Peptidoglycan: is a complex polymer made of polysaccharide linear chains consisting of cross-linked NAM: N-acetylmuramic acid and NAG: Nacetylglucosamine The strands are linked with each other by bridges composed by amino acids. Small group of amino acids (L-alanine, D-alanine, Dglutamic acid and lysine or diaminopimelic acid (DAP) Gram-positive bacteria: • The cell wall contains the teichoic acids. • They can promote the adhesion to the target tissue • They have antigenic properties • They can bind specific proteins: Eg. M protein (streptococci), or A (pneuomococci). The teichoic acid is a virulence factor. The lipoteichoic acid is an endodotoxin. The thick layer of peptidoglycan and the network of teichoic acids represent a significant barrier which opposes the passage of hydrophobic macromolecules such as bile salts present in the intestine of the host. Comparison of the Gram positive and Gram negative bacterial cell walls :Absence of teichoic and lypoteichoic acids. Porin: allow the passive diffusion of small hydrophobic molecules. Gram-negative bacteria: PERIPLASMIC SPACE. Space between the cytoplasmic membrane and the external membrane, containing a thin layer of peptidoglycan and some important enzymes such as: - Hydrolytic enzymes for enzymatic digestion (protease, lipase, phosphatase, enzymes for degrading carbohydrates), of macromolecules important for metabolism; - In pathogens, there are lithic factors of infection (collagenase, ialuronidase, protease). - There are also enzymes (beta-lactamase) that can disrupt antibiotics thus making bacteria resistant to the drug. LPS: Only in gram negative bacteria. It is the endotoxin, a virulence factor which characterizes the pathogenic feature of gram negative bacteria. Antigen O is a long linear polysaccharide with marked antigen properties. Lipid A is the toxic part of the LPS. It interacts with a specific receptors on macrophages and lymphocytes called CD14. This promotes the release of acute phase cytokines (eg. TNFα and IL-1) inducing inflammation. Gram staining: Primary staining: crystal violet hydrophilic, cross the wall and enter the cell which stains with purple Secondary staining: iodine solution, hydrophilic, cross the wall and enter the cell. In Gram + cells, crystal violet and iodine enter target cells, where they combine giving rise to a hydrophobic compound that cannot go out from the cells even with the decoloration. In Gram negative bacteria, the crystal violet and iodine cannot enter properly the outer membrane, and when entered it can be removed with the decoloration. The peculiar Cell wall structure of Mycobacterium: Mycolic acids are linked to the peptidoglycans through a bridge of arabinogalactans. - Mycolic acids can bind different glycolipids, thus forming the waxes - Waxes protect mycobacteria from drying, and disinfectants. They allow bacterial survival for prolonged time despite adverse conditions. •The waxes do not allow the entrance of Cristalviolet into the bacterial cell • Mycobacteria can be stained by the Ziehl-Neelsen staining that contains fuchsin mixed with phenol. • Fuchsin can bind the mycolic acids PEPTIDOGLYCAN is essential for the structure, form, replication and survival of bacteria. It interferes with phagocytosis during infection, it is mitogenic for lymphocytes and acts as pyrogenic. It is degraded by lysozyme present in tears and mucus. Peptidoglycan monomers are synthesized in the cytosol of the bacterium where they attach to a membrane carrier molecule called bactoprenol, The bactoprenols transport the peptidoglycan monomers across the cytoplasmic membrane and helps insert them into the growing peptidoglycan chains, New peptidoglycan synthesis occurs at the cell division plane by way of a collection of cell division machinery known as the divisome. A group of bacterial enzymes called autolysins, located in the divisome, break the glycosidic bonds between the peptidoglycan monomers at the point of growth along the existing peptidoglycan. They also break the peptide cross-bridges that link the rows of sugars together. In this way, new peptidoglycan monomers can be inserted and enable bacterial growth, Transglycosidase enzymes catalize the formation of glycosidic bonds between the NAM and NAG of the peptidoglycan momomers and the NAG and NAM of the existing peptidoglycan. Finally, transpeptidase enzymes reform the peptide cross-links between the rows and layers of peptidoglycan to make the wall strong. This cross-link reaction is catalyzed by transpeptidase (inside cell membrane) and by carbossipeptidase Both enzymes are known as penicillinbinding protein (PBP) PBP are targets for penicillin and other betalactam antibiotics Bacteria penicillin-resistant change PBP structure. Vancomicine It binds the peptides of the peptidoglycan monomers and blocks the formation of glycosidic bonds between the sugars by the transglycosidase enzymes. It is active against Staphylococchi oxacillinresistant and other gram+ resistant to beta-lactam antibiotics It is inactive against gram - : large molecule does not pass though outer membrane of gram -ve. Among Bacteria, Chlamydiae and Mycoplasma do not have the peptidoglycan. Many bacteria both Gram+ and Gram- have an additional layer called capsule composed by polysaccharides. The capsule allows the adherence to the tissue and protects bacteria from phagocytosis. • Plasmids can carry genes that encode toxins or proteins that promote the transfer of the plasmid to other cells but usually do not include genes that are essential for cell growth or replication. • Many plasmids contain mobile DNA sequences (transposons) that can move between plasmids and between plasmids and the chromosome. Genetic exchange between bacteria: -Conjugation -Transformation Transduction • Conjugation is the process by which bacteria transfer genes from one cell to another by cell-tocell contact. the process requires the presence on the donor cell of a hairlike projection called a sex pilus Transformation: Bacterial transformation is a process of horizontal gene transfer by which some bacteria take up foreign genetic material (naked DNA) from the environment. Adsorption Incorporation Recombination in the chromosome of the receiving cell Acquisition of new characters by the receiving cell. Transduction refers to transfer of genes from one cell to another via a phage vector without cell-to-cell contact. The transducing phages are defective because of Bacterial DNA might replace phage DNA. Virulence factors • constituents of the bacterial cell or • products of bacterial metabolism. outside the body (C. botulinum), inside the body (C. tetani). Adhesion: Pseudomonas aeruginosa (Gram-) ØAdhesion to skin cell is mediated by pili. ØP. aeruginosa produce an alginate mucous layer that: allow the anchoration of bacteria to the cell surface, particularly in patients suffering from cystic fibrosis or other respiratory diseases. The mucous layer allows the adherence to heart valves or catheters. Adhesion: Streptococcus pyogenes (Gram+) ØAdhesion ability given by protein F and lipotheic acid on fimbriae. ØAdhesion occurs at the level of certain receptors host cell, fibronectin, widely spread in our organism (vessels, tissues, secretions, extracellular matrix). Capsule and peptidoglycan interfere with phagocytosis. Esoenzymes Spread of bacteria (gram+/-) in tissues. Some esoenzymes: Grampositive bacteria Ø Hyaluronidase: depolymerizes hyaluronic acid, fundamental substance of the connective tissue (S. pyogenes, S.aureus) Ø Collagenase: dissolves collagen, a component of muscular tissue (C. perfringens) Ø Coagulase: determines the enveloping of fibrinogen around bacterial cell, interfering the phagocytosis (S. aureus) Ø Staphylokinase (S. aureus) – Streptokinase (S. pyogenes) Convert plasminogen into plasmin, a proteolytic enzyme able to transform fibrin coagula into soluble products. Ø Catalase: catalizes the decomposition of hydrogen peroxide to water and oxygen (S. aureus) Some esoenzymes: Gram-negative bacteria Ø Phospholipase C (P. aeruginosa) degrades lipids and lecithin facilitating tissue destruction Ø Piocyanin (P. aeruginosa) Catalize the production of hydrogen superoxide and peroxide Ø Protease: inactivate IgA (N. gonorrhoeae) Ø Catalase: catalizes the decomposition of hydrogen peroxide to water and oxygen (H. pylori) Ø Urease: neutralize gastric acids (H. pylori) Ø Mucinase: degrades gastric mucus (H. pylori, V. cholerae). Toxins • Main responsible for damage caused to organism in several bacterial infections ØEsoToxins: proteic substances excreted from bacterial cell, produced by both Gram-positive and Gram-negative bacteria. ØEndoToxins: lipopolysaccharid substances, in external membrane of Gram-negative bacteria. Toxins • Generally excreted by extracellular organisms. • Pathogens replicating in the cell can ’t cause serious damages to the cell. Thus toxins tend to be less important in intracellular infections caused by mycobacteria and chlamydia and mycoplasma. Classification of proteic toxins • Neurotropic: active on nervous system cells. • Enterotoxic: active on intestinal mucus. • Pantropic: active on all cells, inhibit proteic syntesis. • Cytolytic: active on cell membranes. Proteic toxins Classified on the basis of the level to which the toxic activity occurs: Øtoxins acting on cell membrane (alpha toxin: S.aureus, C. perfringens) Øtoxins with intra-cell action (choleric toxin, whooping cough, difteric) Øtoxins with extra-cell action (exfoliating toxin S.aureus). Vibrio cholerae toxin is made of two subunits (A and B). •The complete toxin binds to ganglioside receptor GM1 on cell membrane via subunit B; •The active portion (A1) of subunit A enter the cells and activate the adenylate cyclase determining the storage of cAMP; •cAMP causes the secretion of sodium, chlore, potassium, bicarbonate and water, outside from cell, in the intestine. Corynebacterium diphtheriae, is a Gram-positive bacillus: etiologic agent of diphtheria. Corynebacterium diphtheriae produces esotoxin A-B binding to heparin on a similar epidermic growth factor particularly on heart and nervous cells’ surface. Toxin is encompassed by an endocytic vescicle. Subunit A is released in cytoplasm and catalizes diphosphate-ribosylated elongation factor 2 (EF-2) blocking the host cell proteic syntesis. Clostridium tetani is a rod-shaped, anaerobic species of pathogenic bacteria, of the genus Clostridium. Like other Clostridium genus species, it is Grampositive. • Released by post synaptic dendrites, it crosses the synaptic junction and places in presynaptic endings. • Toxin blocks the release of inhibitor neurotransmitters ( GABA and glycine), inhibiting synapses, and deregulating excitatory synapses. This causes SPASTIC paralysis charactierized by a prolonged muscles contraction. • Tetani toxin is a zincendopeptidase that is encompassed and moves from peripheral nervous endings to the central nervous system. Clostridium botulinum is a Gram-positive, rod-shaped, anaerobic, sporeforming, motile bacterium with the ability to produce the neurotoxin botulinum. The botulinum toxin can cause a severe flaccid paralytic disease in humans and other animals. Botulinum toxin is a metal-protease acting on proteins affecting exocytotic processes in neurotransmitters at the level of peripheral synapses. IT BLOCKS THE RELEASE OF ACETYLCHOLINE INDUCING FLACCID PARALYSIS. Endotoxic shock is usually associated to the systemic spread of microorganisms. Endotoxins –Lipopolysaccharides • thermostable • immunogenic, but antibodies cannot neutralize them - Less potent - Inactive for ingestion. Esotoxins –Proteic nature •Thermolable •immunogenic, antibodies can neutralize them - Extreme potency -Some inactive for ingestion. glycolysis : Glycolysis is the metabolic pathway that converts glucose C6H12O6, into pyruvate, CH3COCOO− + H+. The free energy released in this process is used to form the high-energy compounds ATP (adenosine triphosphate) and NADH (reduced nicotinamide adenine dinucleotide). The pentose phosphate pathway is a metabolic pathway parallel to glycolysis that generates NADPH and pentoses (5- carbon sugars). While it does involve oxidation of glucose, its primary role is anabolic rather than catabolic. - Entner–Doudoroff (ED) pathway (occurring only in prokaryotes) There are a few bacteria that substitute classic glycolysis with the Entner-Doudoroff Pathway. They may lack enzymes essential for glycolysis, such as phosphofructokinase-1. This pathway is generally found in Pseudomonas, Escherichia coli, and a few other Gram-negative genera. Very few Grampositive bacteria have this pathway, with Enterococcus faecalis being a rare exception. Most organisms that use the pathway are aerobes due to the low ATP yield per glucose. Citric acid cycle – also known as the tricarboxylic acid (TCA) cycle or the Krebs cycle is a series of chemical reactions used by all aerobic organisms to generate energy through the oxidation of acetate derived from carbohydrates, fats and proteins into carbon dioxide and chemical energy in the form of adenosine triphosphate (ATP) Aerobic respiration is the process by which ATP is produced by cells by the complete oxidation of organic compounds using oxygen. Aerobic Respiration = Glycolysis + Krebs Cycle/oxidative phosphorylation. If oxygen is absent, bacteria are still able to use glycolysis to produce ATP. This can be done through 2 ways: fermentation and anaerobic respiration. Fermentation is the process by which the electrons and hydrogen ions from the NADH produced by glycolysis are donated to another organic molecule. Sugars are the most common substrate of fermentation, and typical examples of fermentation products are ethanol, lactic acid, and hydrogen. Main characteristics of obligate anaerobes: no oxidative phosphorylation fermentation killed by oxygen lack certain enzymes superoxide dismutase, catalase, peroxidase. Main characteristics of Facultative anaerobes: fermentation aerobic respiration survive in oxygen. -The majority of microorganisms that negatively impact food quality and safety are catalase-positive Main characteristics of obligate aerobes grow in presence of oxygen no fermentation oxidative phosphorylation. Why should we know the metabolism of bacteria ? Because we want to know how to inhibit or stop bacteria growth and want to control their metabolism to prolong shelf-life of food products. STREPTOCOCCUS PNEUMONIAE - It is recognized as one of the major human pathogens. - It is ubiquitous. - It is responsible for a wide range of community-acquired infections ranging from forms at the level of the upper respiratory tract to serious and invasive forms such as pneumonia, meningitis and sepsis. MORPHOLOGICAL AND METABOLIC FEATURES: - Grampositive, not exactly spherical in shape but pear-shaped or lanceolate, - Bacterial cells matched in pairs or short chains (especially in liquid medium) - No production of endospores - Very thick capsule - Anaerobes optional, use a type fermentative metabolism - No Lancefield antigen, the C antigen is covalently bound to the cell wall. CULTURAL FEATURES: These bacteria grow in culture medium enriched with organic liquids - In blood agar plates, they form small colonies (1mm) surrounded by a halo of: alpha-hemolysis in the presence of O2 (partial hemolysis) gamma-hemolysis in the absence of O2 (no hemolysis) Unlike other streptococci, their growth is inhibited by optochin and bile salts. Bile salts act as lithic agents. EPIDEMIOLOGY: These bacteria often reside in the upper respiratory tract. From the upper respiratory tract, they can spread to: - Lungs, where can cause pneumonia - Middle ear where can cause otitis Meninges where can cause meningitis. The main morphological changes in a patient with meningitis are: • Inflammation of the subarachnoid space • Inflammatory involvement of the cerebral vessels • Damage the brain parenchyma. The spread of the bacteria from the upper respiratory tract to lungs is favoured when: - Ciliated epithelium is damaged (from viruses, toxins, smoke), - Accumulation of mucus (as in the cystic fibrosis) People who have CF have thick, sticky mucus that builds up in their airways. This build-up of mucus makes it easier for bacteria to grow and cause infections. Infections can block the airways and cause frequent coughing brings up thick sputum (spit) or mucus that's sometimes bloody., Reduced activity of macrophages. Virulence factors: The capsule is the main factor of virulence of the bacterium: it protects bacteria from phagocytosis and inhibits complement activity. The capsule is composed of polysaccharides in which units of 2 or 7 monosaccharides are repeated. According to the different polysaccharides present in the capsule, > 90 serotypes of pneumococci have been recognized. Factors that mediate colonization in the oropharynx and subsequent migration to the lungs: Pneumolysin: it is a member of a large family of highly conserved, cholesterol binding toxins. It specifically acts on ciliated epithelial cells. It is a cholesterol-dependent cytolysin that creates pores in cholesterol-containing membranes, IgA Protease: it act on the secretory IgA present in epithelia, Neuraminidase, Hyaluronidase, Protein adhesins. The current vaccine contains 23 types of capsular polysaccharides that can induce an antibody response. STAPHYLOCOCCI MORPHOLOGICAL CHARACTERISTICS: - Bacteria are spherical, Gram positive, arranged in bunches - Motionless - Encapsulated - No production of endospores. METABOLIC CHARACTERISTICS: Aerobic, Aaerobic-optional. CULTURE CHARACTERISTICS: -They grow well on common culture media. - They can grow in presence of high salt concentrations: NaCl 7.5% up to 10% - Even if they do not produce endospores, they are resistant to warming, drying and many disinfectants. THE GENUS STAPHYLOCOCCUS COMPRISES 32 SPECIES. MAIN SPECIES PATHOGENIC FOR HUMANS: S. aureus produces coagulase, S. epidermis coagulase-negative, S. saprophiticus coagulasenegative. Coagulase: determines the enveloping of fibrinogen around bacterial cell, interfering the phagocytosis, converts the fibrinogen in fibrin. STAPHYLOCOCCUS AUREUS - Common healthy carrier status - This bacterium is part of the microbial flora in the skin, nose, and in pharynx. It does not produce disease in the normal setting but establish disease when they are introduced into unprotected sites (e.g., blood, tissues). - In solid media, it produces golden-colored colonies due to production of carotenoids , It ferments the mannitol. - The capsule is composed by uronic acid, is immunogenic. The capsule can proctect bacteria from phagocytosis. - The clumping factor is a coagulase that is linked to the cell. The coagulase converts the fibrinogen in fibrin. The fibrin covers the bacterium and protects it from phagocytosis. Protein A • Only present in S. aureus • Critical for evasion from immune system. • Protein A binds IgG molecules by their Fc region. • In serum, the bacteria will bind IgG molecules in the wrong orientation on their surface, which disrupts opsonization and phagocytosis. Cytotoxins: They induce the formation of pores on cellular membrane of many cellular types. 6 Enterotoxins - They are resistant to heat and to proteolytic enzymes. They acts as superantigens, They bind receptors in gastrointestinal mucosa causing vomiting. Shock Syndrome Toxin: It acts as superantigen inducing a potent immune stimulation. Exfoliative toxin : It breaks desmosomes in cellular granular layer of the epidermis. • Superantigens stimulate T cells non-specifically without normal antigenic recognition. It is not internalized by the APC as a normal antigen. • Up to 1 out of 5 T cells may be activated, whereas only 1 out of 10,000 are stimulated during a usual antigen presentation. Cytokines are released systemically in large amounts causing the toxic shock syndrome. • Superantigens bind directly to class II major histocompatibility complexes of antigen-presenting cells outside the conventional antigen-binding grove. • Strains of S. aureus producing shock syndrome toxin grow in vagina (50% infections) or in a wound and release the toxin in the blood • It was associated with use of menstrual towels in which bacterium replicate and produce toxin • Widespread macular rash, high fever, hypotension. Staphylococcal scalded skin syndrome or Ritter's disease: • This toxin causes scalded skin syndrome in neonates, which results in widespread blistering and loss of the epidermis. • The fetus contracts infection at birth (connatal infections), toxin spreads systemically. Lipolytic enzymes degradation of lipids (sebum) with antimicrobial activity in the skin. impetigo with development of vescicles filled with pus. cutaneous infections •Folliculitis: pyogenic infection of hair follicles and in sweat glands‘ ducts of armpit, face, gluteus. Furuncles, Favuses. Epidemiology: They are ubiquitous: skin, oropharynx, gastrointestinal and urogenital tract. Colonize residual umbilical cord and perineal area of newborns. On blood agar plates: -S. aureus forms golden colonies. - S. epidermis forms white colonies. S. epidermidis interacts with plastic materials: artificial heart valves, catheters, shunts and other prosthetic structures. The organism produces slime, which forms a hydrophobic biofilm. This film is adhesive to hydrophobic biopolymers of prosthetics, creating diseases such as endocarditis. S. saprophyticus: often found in young sexually active women as a cause of urinary tract infection with dysuria and pyuria. MYCOBACTERIA • Bacilli (rod-shaped bacteria) • Obligate aerobe (they grow only in presence of oxygen) • No production of endospores • Motionless. Currently, more than 150 species of mycobacteria have been described, many of which are associated with human disease. Despite the abundance of mycobacterial species, the following few species or groups cause most human infections: •M. tuberculosis, •M. leprae, •M. avium complex, •M. kansasii, •M. fortuitum, •M. chelonae, •M. abscessus. M. tuberculosis: causative agent of tuberculosis M. bovis: causative agent of bovine tuberculosis transmitted to humans by food M. leprae: causative agent of leprosy The remaining mycobacteria are environmental organisms collectively known as MOTT (mycobacteria other than tuberculosis) The MOTT are responsible for opportunistic infections especially in immunocompromised patients. Growth properties and colonial morphology are used for the preliminary classification of mycobacteria. M. tuberculosis and closely related species in the M. tuberculosis complex are slow-growing bacteria. The colonies of these mycobacteria are either non pigmented or a light tan color. The other mycobacteria, now referred to as “nontuberculous mycobacteria” (NTM), were classified originally by Runyon by their rate of growth and pigmentation. The pigmented mycobacteria produce intensely yellow carotenoids, which may be stimulated by exposure to light (photochromogenic organisms Figure 25-3) or produced in the absence of light (scotochromogenic organisms). The Runyon classification scheme of NTM consists of four groups: 1. Slow-growing photochromogens (e.g., M. kansasii, M. marinum), 2. Slow-growing scotochromogens (e.g., M. gordonae—a commonly isolated nonpathogen), 3. Slow-growing nonpigmented mycobacteria (e.g., M. avium, M. intracellulare), 4. Rapidly growing mycobacteria (e.g., M. fortuitum, M. chelonae, M. abscessus). NTM and Mycobacterium tuberculosis differ in terms of pathogenicity, infection rates and transmission routes. Gastroesophageal reflux disease has been indicated as a mediator of NTM lung disease • Swallowing of NTM followed by gastric reflux leading to aspiration into the lung. Biofilm formation and hydrophobic characteristics allow colonisation of unfavourable habitats and easy spread. NTM disease: 4 main manifestations: Pulmonary disease, Disseminated disease, Lymphatic disease, Skin/soft tissue disease. • Probability that TB will be transmitted depends on: – Infectiousness of person with TB disease – Environment in which exposure occurred – Length of exposure – Virulence (strength) of the tubercle bacilli. Mycobacterium tuberculosis • Mycobacteria do not produce exotoxins. • Their pathogenicity is mediated by their ability to resist to the intracellular killing of macrophages. • They inhibit the fusion between phagosome and lysosome. So they remain in the phagosomes and replicate. • The genome of mycobacteria contains a region called RD1 encoding the proteins that inhibit the fusion between the phagosome and lysosome. PRIMARY INFECTION • M. tuberculosis is transmitted by the aerosol produced by coughing of infected individuals. • They are very resistant to drying, thus they can persist in the air becoming part of dust particles. • From the upper respiratory tract, they move towards lungs in the alveoli. • Tubercle bacilli multiply in alveoli, where infection begins. • In the alveoli, Mycobacteria bacilli are phagocytized by macrophages. • Some mycobacteria survive inside macrophages, other are killed. • Those macrophages that have not been killed by mycobacteria migrate to lymph-nodes where CD4+ T-naïve lymphocytes are present. Infected macrophages activate T-naïve lymphocytes in Th1 lymphocytes. • Th1 lymphocytes migrate into the alveoli, where activate macrophages and other CD8 + cytotoxic T lymphocytes. • The induction of an immune response against mycobacteria leads to the formation of a granuloma. What is granuloma? Macrophages that do not succeed to kill mycobacteria are surrounded by activated lymphocytes. Outside lymphocytes, there is a layer of fibroblasts and the deposition of calcium salts. When immune response is not sufficient to control bacterial replication, there is: - A continous expansion of granuloma - Migration of mycobacteria to other organs: Extrapulmonary tuberculosis Evolution towards a systemic form of the disease: Miliary tuberculosis. When immune response is sufficient to control bacterial replication: - mycobacteria are contained within the granuloma, that undergoes a phenomenon of fibrosis, and calcification LATENT TUBERCULOSIS: Infection by mycobacterium cannot be eradicated. SECONDARY INFECTION: In case of immune-suppression, latent tuberculosis can reactivate favoring the dissemination of mycobacteria. In an HIV-infected person, TB can develop in one of two ways: • Person with LTBI becomes infected with HIV and then develops TB disease as the immune system is weakened • Person with HIV infection becomes infected with M. tuberculosis and then rapidly develops TB disease. - The diagnosis is usually based on the search of mycobacteria in the biological sample (expectoration). - The expectoration must first be decontaminated with a solution containing sodium hydroxide to which the mycobacteria are resistant. This serves to eliminate other bacteria present in the expectoration. Intradermal tuberculin test - Koch's Tuberculin test was first used. It was obtained from the cultivation of tubercular bacilli, boiled and then filtered. It may contain some active bacterial proteins. - PPD (purified protein derivative) skin test is now used. It is a mix of different tubercolar proteins precipitated from Koch's tuberculin. -Intradermal tuberculin test allows to verify the presence of immune responses against M. tuberculosis by intradermal injection of tuberculin (Mantoux reaction). -Tuberculin is a protein antigen of M. tuberculosis that, inoculated subcutaneously, produces an inflammatory reaction (hypersensitivity type IV) only in patients that had a contact with the bacterium. - This test is used as screening of infected subjects. -The positivity, however, is not a sign of active infection. Isoniazid and ethionammide: affect the synthesis of mycolic acid Ethambutol: interferes with the synthesis of arabinogalactan Cycloserine: inhibits two enzymes, D-alanine synthetase and alanine racemase, that catalyse the synthesis of cell wall. - Daptomycin. It binds irreversibly to the cytoplasmic membrane, resulting in membrane depolarization and destruction of the ionic gradients, ultimately leading to cell death. It has potent activity against Gram positive bacteria GRAM NEGATIVE BACTERIA NESSERIA MENINGITIS • Gram-negative, asporigen, with a polysaccharide capsule • Coffee-bean shaped bacteria organized in pair. Ø Person-to-person spread occurs via aerosolization of respiratory tract secretion Neisseria meningitidis causes: - meningitis, - fulminant septicemia - mild meningococcemia in children and young adults. • Lipopolysaccharides (LPS) are surface components of the outer membrane of Neisseria meningitidis. Today, 12 different types of meningococcal LPS (immunotypes) are known. The triad of fever, nuchal rigidity, and change in mental status is found in two thirds of patients; however, the negative predictive value of these symptoms is high. Bacteria responsible for meningitis are usually capsulated bacteria that have the ability to adhere to the nasopharynx respiratory epithelium. They are translocated through the mucosa in the circulatory stream where, thanks to the capsule, they resist the attacks of phagocytes and complement. The presence of the capsule is the most important virulence factor, along with the presence of proteases that break IgAs. • It is a frequent host of the upper respiratory tract. From 2 to 30% of the healthy population hosts meningococci in the nose and throat without presenting any symptoms and this presence is not related to an increased risk of meningitis or other serious illnesses. • It is transmitted from person to person through respiratory secretions and the main cause of the infection is represented by healthy carriers of the bacterium: only in 0.5% of cases, in fact, the disease is transmitted by people with clinically manifest disease. • During the acute phase of dissemination there is often an esantema, which can result in the formation of confluent pigeons and areas of skin necrosis. Among the 13 identified capsular types of N. meningitidis, six (A, B, C, W135, X, and Y) account for most disease cases worldwide. Neisseria gonorrhoeae • Family: Neisseriaceae • Genere: Neisseria • Gramnegative, asporigen, with a polysaccharide capsule • Coffee-bean shaped bacteria organized in pair • Exclusive human pathogen • Extremely labile outside of the organism because subject to deydration • The capsule of gonococcous is less evident than in Neisseria meningitidis. Common human sexually transmitted infection The bacterium can be transmitted mainly by: - Sexual route, Vertical route, a mother may transmit gonorrhea to her newborn during childbirth; when affecting the infant's eyes, it is referred to as ophthalmia neonatorum. Gram stain of Neisseria gonorrhoeae, the agent of the STD gonorrhea. The bacteria are seen as pairs of cocci (diplococci) in association with host polymorphonuclear leukocytes. IS THE ETHILOGICAL AGENT OF GONORROHEA (colloquially known as the clap). - The usual symptoms in men are burning with urination and penile discharge. Women, on the other hand, are asymptomatic half the time or have vaginal discharge and pelvic pain. - In both men and women if gonorrhea is left untreated, it may spread locally causing epididymitis or pelvic inflammatory disease or throughout the body, affecting joints and heart valves. Treatment is commonly with ceftriaxone as antibiotic resistance has developed to many previously used medications. H.INFLUENZAE: small, pleomorphic, gram-negative coccobacilli } frequently found as normal flora in the upper respiratory tract of humans } can spread by airborne droplets or direct contact with secretions } Meningitis is caused by the encapsulated type B strain } It primarily affects infants younger than 2 years. Its isolation in adults suggests the presence of an underlying medical disorder, including sinusitis, otitis media, alcoholism, CSF leak following head trauma, hyposplenism and hypogammaglobulinemia. Enterobacteriaceae • gastrointestinal diseases – Escherichia coli – Salmonella – Shigella – Yersinia entercolitica. Enterobacteriaceae gram negative facultative anaerobic rods – oxidase negative (no cytochrome oxidase). • E. coli – lactose positive – not usually identified – lactose positive sp. common, healthy intestine • Shigella, Salmonella,Yersinia – lactose negative – identified. Serotypes • reference laboratory – antigens • O (lipopolysaccharide) • H (flagellar) • K (capsular). Shigella: S. flexneri, S. boydii, S. sonnei, S. dysenteriae. bacillary dysentery, shigellosis, bloody feces, intestinal pain pus. SHIGELLA • Gram-negative bacilli, no production of endospores; motionless • The Shighella are divided into 4 subgroups: Shigella A: Shigella dysenteriae. It doesn't ferment the mannitol, and includes 10 serotypes. Produces a termolabil eso-toxin (Shiga toxin) Shigella B: Shigella flexneri. Ferments the mannitol, and includes 8 serotypes. Produces an eso-toxin. Shigella C: Shigella boydii. Ferments the mannitol and includes 15 serotypes. It differs from the subgroup B for other biochemical characters. Shigella D: Shigella sonnei. Ferments the mannitol and lactose. Includes 2 serotypes. The causative agent of human shigellosis, Shigella causes disease in primates, but not in other mammals. During infection, it typically causes dysentery. SHIGELLOSIS: All these bacilli are the causative agent of bacillary dysentery, a disease characterized by a short incubation period (3-6 hours) and violent symptoms such as diarrhea containing blood, mucus and pus. Diarrhea is associated with fever, nausea, abdominal pain, tenesmus (painful spasm of the anal sphincter with an urgent stimulus to defecation). Dysentery can be contracted as a result of: -ingestion of water or food contaminated by fecal material of infected individuals (sick or healthy carriers or convalescent) - Use of contaminated utensils. The molluscs, crustaceans and other seafood consumed raw are particularly dangerous, but also the raw milk and vegetables can act as vehicles of infection. Insects, especially flies, can act as passive carriers of pathogenic organisms. The man, sick or as carrier, is the only source of infection. -The shigellae are introduced with food, are resistant to the gastric barrier and colonize the epithelium of the colon. These bacilli invade and replicate in cells of the colon. - They induce a rearrangement of actin that allow them to move to adjacent cells. THIS ALLOWS SHIGELLOSIS TO ESCAPE FROM THE IMMUNE SYSTEM. Shiga toxin can damage the intestinal epithelial cells. The action of the toxin combined with the action of the immune system causes the damage to the intestinal mucosa. It can also spread through the mucosa, enters the bloodstream and act on: - Glomerular epithelial cells. The damage can cause kidney failure. Cells of the central nervous system. This can sometimes lead to coma. A toxin with similar physiological effects is also produced by group B Shigellae flexneri All the other shigellae do not produce exotoxins and their cytotoxic action is mediated only by LPS (endotoxin). Escherichia coli • Family: Enterobacteriaceae • Genere: Escherichia • Gramnegative • Rod-shaped bacterium commonly found in the lower intestine. Facoltative anaerobic E. coli is the most common and important member of the genus Escherichia. This organism is associated with a variety of diseases, including gastroenteritis and extraintestinal infections, such as urinary tract infection, meningitis, and sepsis. A multitude of strains are capable of causing disease, with some serotypes associated with greater virulence (e.g., E. coli O157 is the most common cause of hemorrhagic colitis and hemolytic uremic syndrome). The harmless strains are part of the normal flora of the gut (0.1%), and can benefit their hosts by producing vitamin K and by preventing the establishment of pathogenic bacteria within the intestine. Fecal-oral- transmission is the major route through which pathogenic strains of the bacterium cause disease. Five different pathogenic groups cause gastroenteritis: Enterotoxigenic (ETEC), Enteropathogenic (EPEC) ,Enterohemorrhagic (EHEC) ,Enteroinvasive (EIEC), Enteroaggregative (EAEC). Escherichia strains possess specialized virulence factors that can be placed into two general categories: adhesins and exotoxins. Enterotoxigenic E. coli - They adhere to the intestinal epithelium, cannot invade the intestinal mucosa - They produce an exotoxin whose mechanism of action is similar to that observed to the Vibrio Cholerae toxin (Heat-labile exotoxin (LT1)) - They cause watery diarrhea that does not produce histopathological lesions in the mucosa. - Toxigenic strains are the leading cause of infant diarrhea in developing countries and the "traveler's diarrhea". Site of action: small intestine. Virulence factor: 2 classes of toxins 1. Heat-labile exotoxin (LT-1) 2. Heatstable enterotoxin (STa) Only some strains of ETEC produce these toxins. Heat-labile toxin is made of two subunits (A and B). •The complete toxin binds to ganglioside receptor GM1 on cell membrane via subunit B; •The active portion (A1) of subunit A enter the cells and activate adenylate cyclase determining cAMP accumulation; •cAMP causes the secretion of sodium, chlore, potassium, bicarbonate and water, outside from cell, in intestines. Enteropathogens E. coli They strongly and tightly adhere to the intestinal epithelium. The tight adhesion determines the destruction of microvilli, resulting in a reduced absorption of nutrients. The accumulation of these substances in gut lumen leads to an osmotic passage of water into the intestinal lumen, causing watery diarrhea. Important cause of infant diarrhea, particularly in developing countries. Enteroinvasive E. coli • They have the ability to penetrate inside the epithelial cells of the intestinal mucosa through a mechanism of receptor-mediated endocytosis. • They replicate inside the epithelial cells and kill them •Necrosis of the epithelium is accompanied by a massive inflammatory reaction. Clinical manifestations: dysentery with blood and pus in the stool (similar to Shigellosis). Enterohemorrhagic E. coli • They have not invasive properties • They adhere intestinal epithelium and produce Shiga-like toxin. • The toxin kills the epithelial cells thus destroying the intestinal mucosa. This causes bleeding. The action of the toxin on glomerular endothelial cells can produce kidney failure. It causes diarrhea acute and chronic. H. pylori[Curved, gram-negative rods] is found in the gastric mucous layer or adherent to the epithelial lining of the stomach. H. Pylori is an important cause of acute and chronic gastritis, peptic ulcers (causing more than 90% of duodenal ulcers and up to 80% of gastric ulcers), gastric adenocarcinoma, and mucosalassociated-lymphoid-type (MALT) lymphoma. Humans are the primary resevoir Ø Person to person spread is important (typically fecal-oral). The standard first-line therapy is a one-week "triple therapy" consisting of proton pump inhibitors such as omeprazole and the antibiotics clarithromycin and amoxicillin. the breath test. In this test, the patient is given either 13C- or 1 4C-labeled urea to drink. H. pylori metabolizes the urea rapidly, and the labeled carbon is absorbed. This labeled carbon can then be measured as CO2 in the patient’s expired breath to determine whether H. pylori is present. The sensitivity and specificity of the breath test ranges from 94% to 98%. Helicobacter pylori: Diagnosis Also, a urine ELISA test with a 96% sensitivity and 79% specificity is available. The bacterium lives only in acidic environment protected by a layer of mucus; for this reason it is found only in the stomach. Once it is in the stomach, provides to the mucosa toxic metabolites. The bacteria can produce substances that cause damage to cells and over time can occur gastritis and ulcer. Salmonella infections spp.: Sources Maximum spread in warm months. The infection is often contracted after ingestion of undercooked food (prepared on work surfaces contaminated). Salmonella: - often present on or in eggs - often transmitted by food handlers The dose required to give symptomatic disease is between 106 – 108 cells (it is reduced with the age of people, immunosuppression, acloridria). S. Enteritidis: diarrhea the common salmonella infection (salmonellosis) poultry, eggs no human reservoir Gastroenteritis nausea vomiting non-bloody stool fever (38-39°C) self-limiting (2 - 7 days) Salmonella Uncomplicated cases (the vast majority) antibiotic therapy not useful. S. Choleraesuis much less common animal reservoir septicemia antibiotic therapy essential. Enteric fever (typhoid): S Typhi, Paratyphi A, Paratyphi B, Paratyphi C. It ' s a form of systemic salmonellosis. The best known form is typhoid fever , caused by S. Typhi , but other species of Salmonella can cause this type of disease. Symptoms appear after an incubation period of 10- 14 days. Enteric fever may be preceded by gastroenteritis , which is resolved before the systemic disease. Enteric fever can be fatal without antibiotic therapy. Salmonella typhi human reservoir carrier state common contaminated food water supply poor sanitary conditions. Dissemination of S. Typhi during systemic infection. In the small intestine the bacteria adhere to the mucosa and then invade the epithelial cells. Specialized epithelial cells such as