Bacterial Physiology & Growth PDF

Bacteria Growth and Physiology Dr. Mohamed Elmutasim Microbiology Department 26 Sep. 2022  Bacteria Growth Bacterial Reproduction: Bacteria reproduce by binary fission, a process by which one parent cell divides to form two progeny cells. ...

Bacteria Growth and Physiology Dr. Mohamed Elmutasim Microbiology Department 26 Sep. 2022  Bacteria Growth Bacterial Reproduction: Bacteria reproduce by binary fission, a process by which one parent cell divides to form two progeny cells.  Bacterial Growth Curve Exponential growth (logarithmic growth): one cell gives rise to two progeny cells The doubling (generation) time of bacteria: It is the time it takes for a population of bacteria to double in number. It ranges from 20 minutes for Escherichia coli to more than 24 hours for Mycobacterium tuberculosis. The growth cycle of bacteria has four major phases: 1- The lag phase: During which metabolic activity occurs but cells do not divide (few minutes up to many hours). 2- The log (logarithmic or Exponential ) phase: Rapid cell division occurs. β -Lactam drugs (e.g. penicillin) act during this phase because they are effective when cells are dividing. 3- The stationary phase: Nutrient depletion or toxic products cause growth to slow until no. of new cells balances no. of cells death resulting in a steady state. 4-The death phase: - Decline in the number of viable bacteria. Bacterial Growth Curve  Factors Influencing Bacterial Growth Physical Requirements Nutritional Requirements 1. Temperature 1- Energy source 2. Oxygen requirements 2- Carbon source 3. PH 3- Nitrogen source 4. Osmosis 4- Minerals - Sulfur - Phosphorus - Potassium, magnesium & calcium - Iron - Trace elements 5- Water 6- Growth factors  Factors Influencing Bacterial Growth: Physical Requirements 1-Temperature Definition Optimum growth temperature Psychrophiles Cold-loving bacteria Between – 5C and 15C. Mesophiles Bacteria that grow Between 20C and 40C. at moderate Most bacteria are temperatures. mesophilic & include soil bacteria and bacteria that live in and on the body. Thermophiles Heat-loving bacteria Between 45C and 70C. Hyperthermophiles Bacteria that grow Between 70C and 110 C. at very high temperatures  Physical Requirements 2- Oxygen requirements: Definition They obtain energy through Obligate aerobes Grow only in the presence of oxygen Aerobic respiration Microaerophiles - Require a low concentration of Aerobic respiration oxygen (2% to 10%) for growth - Higher concentrations are inhibitory Obligate anaerobes Grow only in the absence of oxygen - Anaerobic respiration (inhibited or killed by its presence). -or fermentation Aerotolerant - Cannot use oxygen to transform Only by fermentation anaerobes (obligate energy fermenters ) - Can grow in its presence. Facultative - Grow with or without oxygen -Aerobic respiration if anaerobes - But generally better with oxygen. oxygen is present Most bacteria - Fermentation or anaerobic respiration if it is absent. Physical Requirements  4- Osmosis Osmosis is the diffusion of water across a membrane: -From higher water concentration (lower solute concentration) -To lower water concentration (higher solute concentration) Osmosis does not require energy. 4- Osmosis Factors Influencing Bacterial Growth: Nutritional Requirements  Respiration: 1- Aerobic Respiration It is glucose catabolism under aerobic conditions. This results in energy production in the form of 38 ATP molecules. Aerobic respiration involves : The final electron acceptor is molecular O2 2- Anaerobic Respiration: It occurs in the absence of oxygen. The final electron acceptor is an organic molecule such as nitrate, sulfate, or CO2 The net yield of ATP molecules is less than it is with aerobic respiration.  3- Fermentation It is the process of extracting energy from the oxidation of organic compounds, such as carbohydrates. It is the process by which facultative bacteria generate ATP in the absence of oxygen. 2- Carbon Source  3- Nitrogen Source Nitrogen Sources are: - Nitrogen - Nitrates - Ammonia - Organic nitrogen compounds Nitrogen is needed for the synthesis of: - Amino acids - DNA - RNA - ATP  4- Minerals 1. Sulfur: It is needed to synthesize sulfur-containing amino acids and certain vitamins. 2. Phosphorus: It is needed to synthesize phospholipids, DNA, RNA & ATP. Phosphate ions are the primary source of phosphorus. 3. Potassium, Magnesium and Calcium: These are required for certain enzymes. 4. Iron: It is a component of cytochromes and other enzymes. 5. Trace Elements: They are required in very minute amounts and function as cofactors (electron donors or acceptors) in enzyme reactions. They include sodium, zinc, copper, molybdenum, manganese, and cobalt ions. 5- Water & 6- Growth factors: Growth factors are organic compounds such as: - Amino acids - Purines - Pyrimidines - Vitamins Cells must have them for growth but cannot synthesize them. Fastidious Organisms: They have complex nutritional requirements & need many growth factors. Thank You  Bacterial Introduction and Structure Dr. Mohamed Elmutasim Microbiology Department 26 Sep. 2022  Microbiology -Microbiology is the study of microorganisms, which are microscopic, unicellular, and cell-cluster organisms. -Medical microbiology deals with the study of microorganisms that are of medical importance and cause diseases in human beings.  Structure of Bacterial Cells Shape & Size The size of most bacteria ranges from 1 to 3 μm. Mycoplasma, the smallest bacteria (smallest cells) are 0.2 μ m. Bacteria have three shapes: - cocci (spheres) - bacilli (rods) - spirochetes (spirals) Cocci are arranged in three patterns: - Pairs (diplococci) - Chains (streptococci) - Clusters (staphylococci) The shape of a bacterium is determined by its rigid cell wall. The microscopic appearance of a bacterium is an important criterion used in its identification.  Bacterial Cell Wall All bacteria have a cell wall composed of peptidoglycan except Mycoplasma, which is surrounded only by a cell membrane. Gram-negative bacteria have a thin peptidoglycan covered by an outer lipid-containing membrane Gram-positive bacteria have a thick peptidoglycan & no outer membrane. These differences explain why: -Gram-negative bacteria lose the stain when exposed to a lipid solvent in the Gram stain process - Gram-positive bacteria retain the stain and remain purple. Comparison of Cell Walls of Gram-Positive and Gram-Negative Bacteria  Gram stain Gram-positive bacteria stain purple, whereas gram- negative bacteria stain pink. Gram-positive bacteria can retain crystal violet–iodine complex in the presence of lipid solvents such as alcohol. Gram-negative bacteria lose purple dye when treated with alcohol (have outer lipid-containing membrane & thin peptidoglycan) & become colorless & then stain pink when exposed to red dye such as safranin.  Peptidoglycan -It is found only in bacterial cells. -It is a network that covers the entire bacterium. -Function: a. gives the organism its shape. b. The site of action of penicillins & cephalosporins -It is composed of a sugar backbone (glycan) and peptide side chains (peptides). The side chains are cross-linked by transpeptidase (The site of action of penicillins & cephalosporins which inhibit transpeptidase enzyme)  The outer membrane of gram-negative bacteria Endotoxin (lipopolysaccharide, LPS): Function: The main inducer of septic shock. Endotoxin consists of: - lipid A fever & hypotension in septic shock - polysaccharide(O antigen) use in laboratory identification  The outer membrane of gram-negative bacteria Periplasmic space: -It lies between inner cell membrane & outer membrane of gram-negative bacteria Function: -It is the location of β–lactamases-the enzymes that degrade β -lactam antibiotics, such as penicillins and cephalosporins.  The membrane of bacteria Lysozymes -They kill bacteria by cleaving the glycan backbone of peptidoglycan. -The cytoplasmic membrane of bacteria : -It consists of a phospholipid bilayer (without sterols) located just inside peptidoglycan. -Function It regulates: - Active transport of nutrients into cells. - Secretion of toxins out of the cell.  Cell Walls of Acid-Fast Bacteria -Mycobacteria are acid-fast because they resist decolorization with acid–alcohol after staining with carbolfuchsin. -This is due to the high concentration of lipids in the cell wall. -The dyes used in the Gram stain do not stain mycobacteria. However, they are stained by Ziehl Neilson (ZN).  Bacterial DNA The bacterial genome: It consists of a single chromosome of circular DNA located in a nucleoid. Function: Carry genetic material. Plasmids: They are extrachromosomal pieces of circular DNA Function: encode both exotoxins & enzymes antibiotic resistance Transposons (Jumping genes): They are small pieces of DNA that move between chromosomal DNA and plasmid DNA. Function: They carry antibiotic-resistant genes.  Structures External to the Cell Wall Capsules: -They are composed of polysaccharides (the polypeptide capsule of anthrax bacillus is an exception). Function: a. They are antiphagocytic, i.e., they limit the ability of neutrophils to engulf bacteria. Antibodies against the capsule neutralize the antiphagocytic effect & allow bacteria to be engulfed by neutrophils. Opsonization is the process by which antibodies enhance the phagocytosis of bacteria. b. Capsules are antigens in several vaccines, such as pneumococcal vaccine. c. Specific identification made by using antiserum against the capsular polysaccharide.  Structures External to the Cell Wall The glycocalyx: It is a polysaccharide "slime layer" secreted by certain bacteria. Function: It attaches bacteria firmly to: - Surface of human cells - Surface of catheters - Prosthetic heart valves & hip joints. Pili: They are filaments of protein that extend from the bacterial surface. Function: a. mediate attachment of bacteria to surface of human cells. b. A different kind of pilus, sex pilus, functions in conjugation.  Structures External to the Cell Wall Spores: -They are highly heat resistant & are not killed by many disinfectants. -Boiling will not kill spores. They are formed by certain gram-positive rods, especially Bacillus & Clostridium species. They have a thick, keratinlike coat that allows them to survive for many years, especially in the soil. -Spores are formed when nutrients are in short supply -Spores germinate to form bacteria that can cause disease when nutrients are restored. -They are metabolically inactive but contain DNA, ribosomes & other essential components. Spores Thank You Normal flora & Bacterial Pathogenesis Dr. Mohamed Elmutasim Microbiology Department 2022  Normal flora (commensals) They are those microorganisms that are permanent residents of body that everyone has. Commensals are organisms that derive benefit from another host but do not damage that host. Normal flora (commensals) Normal flora organisms are: Bacteria or yeasts (No Viruses, protozoa & helminths) Inhabit body surfaces exposed to environment, such as : Skin- Oropharynx- Intestinal tract -Vagina. Differ in number & kind at various anatomic sites. Low-virulence organisms. In their usual anatomic site, they are nonpathogenic. If they leave their usual anatomic site, especially in immunocompromised individual disease.  Colonization Some people can be colonized: - -transiently or for long periods - With certain organism (not members of normal flora). Colonization resistance: It occurs when members of normal flora occupy receptor sites on skin & mucosal surfaces preventing pathogens from binding to those receptors. Normal flora Normal flora (commensals)  Bacterial Pathogenesis ▪ Pathogen: are microbes capable of causing disease in immunocompetent people. ▪ Opportunistic Pathogen: It refers to microbes that are capable of causing disease only in immunocompromised people. ▪ Carriers (chronic carriers): Individuals in whom pathogenic organisms are present in significant numbers & are source of infection for others. Bacterial Pathogenesis Infection has two meanings: 1) Presence of microbes in body 2) Symptoms of disease. Presence of microbes in body does not always result in symptoms of disease Bacteria cause symptoms of disease by two main mechanisms: 1) Production of toxins (exotoxins & endotoxins) 2) Induction of inflammation. Bacterial Pathogenesis Virulence: It is measure of microbe's ability to cause disease. Asymptomatic or inapparent Infections: These infections occur when our host defenses have eliminated microorganism before it could multiply to sufficient numbers to cause symptoms of disease. Bacterial Pathogenesis Communicable Infection: Most bacterial infections are communicable, i.e., capable of spreading from person to person. Epidemiologic terms used to describe infections: Endemic :Infections that occur at persistent, usually low level in certain geographic area Epidemics: Infections occur at much higher rate than usual. Pandemics: Infection spread rapidly over large areas of globe Bacterial Pathogenesis Stages of Bacterial Pathogenesis: Transmission: from external source into portal of entry. Evasion: of primary host defenses (skin or stomach acid). Adherence: to mucous membranes, usually by bacterial pili. Colonization: by growth of bacteria at site of adherence. Disease symptoms: caused by toxin production or invasion accompanied by inflammation. Host responses:both nonspecific & specific (immunity). Progression: or resolution of disease. Determinants of Bacterial Pathogenesis: Transmission Determinants of Bacterial Pathogenesis: Transmission Determinants of Bacterial Pathogenesis: Transmission Vertical Transmission: It is transmission of Bacteria, viruses & other microbes from mother to offspring through: Placenta Birth canal during birth Breast milk. Horizontal Transmission: It is person-to-person transmission(from mother to offspring). Zoonoses: Human diseases for which animals are reservoir Determinants of Bacterial Pathogenesis: Transmission The main "portals of entry" into body : Respiratory tract Gastrointestinal tract Skin Genital tract. Determinants of Bacterial Pathogenesis: Toxin Production Determinants of Bacterial Pathogenesis: Toxin Production Exotoxins: Many exotoxins have A–B subunit structure: - A (active) subunit possesses toxic activity - B (binding) subunit is responsible for binding exotoxin to specific receptors on membrane of human cell. Typical Stages of Infectious Disease Incubation period: time between moment person is exposed to microbe (or toxin) & appearance of symptoms. Prodrome period: time during which nonspecific symptoms occur. Specific-illness period: time during which characteristic features of disease occur. Recovery period: time during which symptoms resolve & health is restored. Typical Stages of Infectious Disease After recovery period, some people become: -chronic carriers of organism. -latent infections develop: Some people have subclinical infections during which they remain asymptomatic. Thank You