Medical Microbiology & Immunology Notes 2023/2024 PDF

Medical Microbiology & Immunology ‫ﺣﺒﻴﺒﻪ ﺣﺎﻣﺪ ﻣﺤﻤﺪ ﺳﻠﻴﻤﺎﻥ ﺍﻟﺸﺮﻣﻪ‬ For Faculty of Nursing Condensed program 2023/2024...

Medical Microbiology & Immunology ‫ﺣﺒﻴﺒﻪ ﺣﺎﻣﺪ ﻣﺤﻤﺪ ﺳﻠﻴﻤﺎﻥ ﺍﻟﺸﺮﻣﻪ‬ For Faculty of Nursing Condensed program 2023/2024 2023/2024 2023/2024 By Dr. Sara Youssef Maxwell 1 ‫ﺣﺒﻴﺒﻪ ﺣﺎﻣﺪ ﻣﺤﻤﺪ ﺳﻠﻴﻤﺎﻥ ﺍﻟﺸﺮﻣﻪ‬ PREFACE The aim of this manual is to provide an essential coverage of medical microbiology and immunology for all medical staff if they are to work safety in both hospital and community environments, to maintain asepsis and prevent 2023/2024 2023/2024 2023/2024 the spread of infection. The book is presented mainly for students of Faculty of Nursing to cover all aspects of microbiology , sterilization, laboratory diagnosis of infection. Additionally, brief notes have been included on hospital acquired infections mycology and virology. We would like that this book will be of value for the application of microbiological knowledge and principles. 2 ‫ﺣﺒﻴﺒﻪ ﺣﺎﻣﺪ ﻣﺤﻤﺪ ﺳﻠﻴﻤﺎﻥ ﺍﻟﺸﺮﻣﻪ‬ 2023/2024 2023/2024 2023/2024 Section I: General Microbiology 3  Chapter 1 ‫ﺣﺒﻴﺒﻪ ﺣﺎﻣﺪ ﻣﺤﻤﺪ ﺳﻠﻴﻤﺎﻥ ﺍﻟﺸﺮﻣﻪ‬ Morphology and structure of Micro-organisms Morphological characters of bacteria include the size, shape, staining properties, motility, sporulation, presence of capsule and arrangement. Size: Bacteria are unicellular microorganisms measured in micrometer (1 µm = 0.001 mm, 10-6 meter). Bacteria range in size from about 0.2 to 5 µm. Shape and arrangement (Fig. 1): Bacteria are classified by shape 2023/2024 2023/2024 into three basic groups: 2023/2024 cocci, bacilli and spirochetes. Some bacteria are variable in shape and said to be pleomorphic (many shaped). The shape of a bacterium is determined by its rigid cell wall. The microscopic appearance of a bacterium is one of the most important criteria used in its identification. In addition to their characteristic shapes, the arrangement of bacteria is important. For example, certain cocci occur in pairs i.e. diplococci (Pneumococci), some in chains (Streptococci), and others in grapelike clusters (Staphylococci). Staining properties: www.meningitisuk.org 4 ‫ﺣﺒﻴﺒﻪ ﺣﺎﻣﺪ ﻣﺤﻤﺪ ﺳﻠﻴﻤﺎﻥ ﺍﻟﺸﺮﻣﻪ‬ According to Gram stain, bacteria are divided into 2 groups: Gram positive bacteria that appear violet in colour under the microscope. Gram negative bacteria that appear pink under the microscope. Structure of the bacterial cell The essential components of the bacterial cell are the cell wall, cytoplasmic membrane and the cytoplasm which 2023/2024 2023/2024 2023/2024 contains the nuclear material and other intracytoplasmic structures (ribosomes, plasmids and metabolic granules). Beside these basic structures, some bacteria have surface structures such as capsule, flagellae and pili (Fig 2). Some bacteria may also form endospores. www.schools-wikipedia.org 5  The Cell wall Structure of the cell wall: ‫ﺣﺒﻴﺒﻪ ﺣﺎﻣﺪ ﻣﺤﻤﺪ ﺳﻠﻴﻤﺎﻥ ﺍﻟﺸﺮﻣﻪ‬ The cell wall is the outermost component of bacteria. It is a multilayered structure located external to the cytoplasmic membrane. It varies in thickness and chemical composition depending upon the bacterial type. Cell walls of Gram positive and Gram negative bacteria: The structure, chemical composition and thickness of the cell wall differ in Gram positive and Gram negative bacteria (Fig. 3). Gram positive bacteria: It is composed of: 1. The peptidoglycan layer: innermost layer. It is thick 2023/2024 in Gram positive bacteria,2023/2024 forming about 50% of 2023/2024 the cell wall materials. 2. Fibers of teichoic acid: that protrude outside the Peptidoglycan. Gram negative bacteria: it is composed of: 1. The peptidoglycan layer: the innermost layer. It is very thin in Gram negative bacteria, forming 5-10% of the cell wall materials. 2. Outer membrane: the outermost layer that contains lipopolysaccharide (LPS).. 3. Periplasmic space: It is the space between the inner layer and the outer layer and is filled with gel. 4. Lipoprotein molecules: cross link the peptidoglycan layer and the LPS layer. 6  Functions of the cell wall: 1- It is a rigid structure which gives the shape of the ‫ﺣﺒﻴﺒﻪ ﺣﺎﻣﺪ ﻣﺤﻤﺪ ﺳﻠﻴﻤﺎﻥ ﺍﻟﺸﺮﻣﻪ‬ bacteria. 2- It is osmotically insensitive. It protects the cytoplasmic membrane from bursting in hypotonic solutions. 3- It acts as a channel to allow the entry of essential substance as sugars, amino acids, vitamins and metals, as well as many antimicrobial drugs. 4- It plays a role in cell division. Table (1): Comparison of cell walls of Gram positive and Gram negative bacteria. 2023/2024 2023/2024 2023/2024 Gram-positive Gram-negative Component cells cells ▪ Peptidoglycan Thicker; multilayer Thinner; single layer ▪ Teichoic acids Yes No ▪ Lipopolysaccharide (endotoxin) No yes Cell walls of acid fast bacteria: Acid fast bacteria are characterized by high lipid concentration in the cell wall, especially mycolic acids. This unusual cell wall results in their inability to be Gram-stained and they are stained with Ziehl-Neelsen (Z.N) stain. These bacteria are said to be acid-fast eg. Mycobacterium tuberculosis. Bacteria with defective cell wall: Only Mycoplasma has no cell wall and surrounded by cell membrane. 7  The cell membrane (Cytoplasmic Membrane or Plasma Membrane) ‫ﺣﺒﻴﺒﻪ ﺣﺎﻣﺪ ﻣﺤﻤﺪ ﺳﻠﻴﻤﺎﻥ ﺍﻟﺸﺮﻣﻪ‬ It lies just internal to the cell wall. It is a semi-permeable membrane formed of 2 layers of phospholipids in which proteins and enzymes are embedded. The cytoplasmic membrane has four important functions: 1. Active transport of molecules into the cell. 2. Energy generation by oxidative phosphorylation. 3. Synthesis of precursors of the cell wall. 4. Secretion of enzymes and toxins. 2023/2024 Intracytoplasmic structures 2023/2024 2023/2024 Important contents of the cytoplasm: 1. Nucleoid: is the area of the cytoplasm in which the DNA is located. It is a single circular double stranded DNA molecule (chromosome). There is no nuclear membrane or nucleolus. The DNA carries the genetic information to daughter cells and it is duplicated before cell division. 2. Ribosomes: they are the site of protein synthesis. Ribosomes are spherical particles present in the cytoplasm. 3. Intracytoplasmic inclusions: the cytoplasm contains granules which represent accumulation of food reserve. 4. Plasmids: plasmids are extrachromosomal, double- stranded, circular DNA molecules that are capable of replicating independently of the bacterial chromosome. 5. Transposons: these are non-replicating pieces of DNA that move readily from one site to another within 8  bacteria. Due to their unusual ability to move, they are nicknamed as jumping genes. They can code for drug ‫ﺣﺒﻴﺒﻪ ﺣﺎﻣﺪ ﻣﺤﻤﺪ ﺳﻠﻴﻤﺎﻥ ﺍﻟﺸﺮﻣﻪ‬ resistance enzymes, toxins, or a variety of metabolic enzymes. Surface structures outside the cell wall A- Capsule: The capsule is a gelatinous layer covering the entire bacterium. It is composed of polysaccharide. The sugar components of the polysaccharide vary 2023/2024 from one species of bacteria to another 2023/2024 2023/2024 The capsule is important for four reasons: 1- It is a determinant of virulence of many bacteria, since it limits the ability of phagocytes to engulf the bacteria. N.B: Variants of encapsulated bacteria that have lost the ability to produce a capsule are usually nonpathogenic. 2- Specific identification of an organism can be made by using antiserum against the capsular polysaccharide. 3- Capsular polysaccharides are used in certain vaccines, since they are capable of eliciting protective antibodies. 4- The capsule may play a role in the adherence of bacteria to human tissues. 9  B- Flagella: They are organs of motility in motile bacteria. Flagella ‫ﺣﺒﻴﺒﻪ ﺣﺎﻣﺪ ﻣﺤﻤﺪ ﺳﻠﻴﻤﺎﻥ ﺍﻟﺸﺮﻣﻪ‬ are long, whiplike structure that move the bacteria toward nutrients and other attractants. They are formed of protein subunits called flagellin which is antigenic and differ in different bacterial species. Flagellated bacteria have a characteristic number and location of flagella: some bacteria have one, and others have many; in some the flagella are located at one end, and in others they are all over the outer surface. 2023/2024 2023/2024 2023/2024 Fig. (4): Distribution of bacterial flagellae C- Pili (fimbriae): Pili are hair like projections that extend from the cell surface. They are shorter, thinner and straighter than flagellae. They are composed of subunits of a protein called pilin. They are found mainly on gram negative organisms and help in adherence. Bacterial endospore They are highly resistant resting forms of some Gram positive bacteria. They are formed in response to unfavorable conditions e.g. depletion of nutrients, heat, dryness, etc.). The spore is formed inside the parent vegetative bacterial cell so it is known as endospores. The endospore incorporate the 10  bacterial DNA, a small amount of cytoplasm, cell membrane, peptidoglycan, very little water, and most importantly, a thick keratin like coat known as the cortex that is responsible for ‫ﺣﺒﻴﺒﻪ ﺣﺎﻣﺪ ﻣﺤﻤﺪ ﺳﻠﻴﻤﺎﻥ ﺍﻟﺸﺮﻣﻪ‬ the remarkable resistance of the spore to heat, dehydration , radiation, and chemicals. Once formed, the spore has no metabolic activity and can remain dormant for many years. Upon exposure to water and the appropriate nutrients, specific enzymes degrade the coat; water and nutrients enter; and germination into a metabolizing, reproducing bacterial cell occurs. The medical importance of spores lies in their high resistance to heat and chemicals. As a result, sterilization cannot be achieved by boiling. Sterilization by autoclaving at2023/2024 121° C, usually for 30 minutes, is2023/2024 required to ensure the 2023/2024 sterility of products for medical use. The description of the spore should include: The position of the spore: terminal, sub-terminal and central. The shape of the spore: oval or rounded. The size of the spore in relation to the body of the bacillus (Fig. 5). 11 Fig. (5): Bacterial endospores: shape, size and location  Chapter 2 ‫ﺣﺒﻴﺒﻪ ﺣﺎﻣﺪ ﻣﺤﻤﺪ ﺳﻠﻴﻤﺎﻥ ﺍﻟﺸﺮﻣﻪ‬ Growth and Nutrition of Bacteria I. Growth Requirements of Bacteria A. Bacterial Nutrition: Carbon and nitrogen are the main elements needed for bacterial nutrition. Accordingly bacteria can be classified into: Autotrophs: ▪ Can assimilate simple inorganic sources of carbon and nitrogen. Heterotrophs: 2023/2024 2023/2024 2023/2024 ▪ Require preformed organic sources of carbon, e.g. glucose. ▪ Most of the pathogenic bacteria are heterotrophic in nutrition. ▪ Many can grow on simple media containing peptone or meat extract ▪ Others require complex organic material e.g. blood or serum B-Growth factors (Essential metabolites - Essential nutrients) They include ammo acids, vitamins, coenzymes, Anions of phosphate and sulphate and cations of Na, K, Mg, Ca, Mn and iron are also essential in small amounts for growth. 12  1. Gaseous Requirements Oxygen and CO2, are very essential for bacterial growth. ‫ﺣﺒﻴﺒﻪ ﺣﺎﻣﺪ ﻣﺤﻤﺪ ﺳﻠﻴﻤﺎﻥ ﺍﻟﺸﺮﻣﻪ‬ 1) Oxygen: According to Oxygen requirements, bacteria are classified into: a) Obligatory aerobes: - Grow only in the presence of O2. - e.g. Mycobacterium tuberculosis. b) Aerobe facultative anaerobes: - 2023/2024 Grow well in the presence2023/2024 of O2, as well as in the 2023/2024 absence of O2. - e.g. most pathogenic bacteria as Staphylococci, Streptococci and E. coli. c) Obligatory anaerobes: - Grow only in absence of O2. - May be killed in its presence. - e.g. Clostridium tetani and most of the spirochaetes. - In the presence of O2, strict anaerobes produce peroxides and superoxides which they cannot destroy because they lack the enzymes catalase and superoxide dismutase. Peroxides and superoxides inhibit the growth of anaerobic organisms. 13  d) Micro aerophilics: Grow best in the presence of a trace of O2 and - ‫ﺣﺒﻴﺒﻪ ﺣﺎﻣﺪ ﻣﺤﻤﺪ ﺳﻠﻴﻤﺎﻥ ﺍﻟﺸﺮﻣﻪ‬ often prefer a concentration of CO2. They will not grow in the presence of free O2 nor in its complete absence e.g. Corynaebacteriumacnea. 2) CO2: - All bacteria require a small of CO2 percentage for their growth Some bacteria require a higher percentage of CO2 (5-10%) as brucella abortus. 2. Moisture: 2023/2024 2023/2024 2023/2024 - 4/5 of the weight of bacterial cell consists of water, so moisture is necessary for growth. - Drying is dangerous for life of many bacteria, e.g. gonococci, but some bacteria may survive in a dry place for weeks e.g. T.B bacillus. Also endospores survive drying for a long time. 3. Temperature: For each species of bacteria is an: ❖ Optimum temperature: at which the organism grows best. Bacteria differ with regard to the optimal temperature range for their growth; psychrophile (below 20°C) mesophile (between 25-40°C) and thermophile (between 55 - 80°C). Most medically important species are mesophiles; grow best at temperature 37°C. 14  4. Hydrogen ion Concentration (pH): ‫ﺣﺒﻴﺒﻪ ﺣﺎﻣﺪ ﻣﺤﻤﺪ ﺳﻠﻴﻤﺎﻥ ﺍﻟﺸﺮﻣﻪ‬ Most pathogenic bacteria can grow at an optimum pH around 7.5 with a range 7.2 -7.6. The optimum pH is about that of the body fluids. Some bacteria flourish in acidic pH e.g. Lactobacilli while others prefer alkaline pH e.g. Vibrio cholera (V. cholera). - Influence of light and other radiations: Darkness provides a favorable condition for growth and viability. Ultraviolet and infra-red rays are rapidly bactericidal. Direct sunlight 2023/2024 2023/2024 destroys 2023/2024 bacteria by the action of ultra violet and infra-red rays. - Bacterial Growth Curve If given bacterium is seeded into a suitable liquid medium and incubated at a suitable temperature, the growth of the bacterium will follow a definite course. This course is represented in a graphical form, plotting the logarithms of the number of viable bacteria against the time in hours. The growth curve (Fig. 6) can be divided into four phases: 1. Lag phase: This is the stage of preparation for multiplication, during which the organism adapts itself by the synthesis of new enzymes specific for the new medium. During this period, there is no increase in the number of bacteria and there may be a slight decrease due to death of some of the inoculated bacteria. 15  2. Logarithmic phase This is the phase of rapid multiplication. When the ‫ﺣﺒﻴﺒﻪ ﺣﺎﻣﺪ ﻣﺤﻤﺪ ﺳﻠﻴﻤﺎﻥ ﺍﻟﺸﺮﻣﻪ‬ logarithm of number of viable organisms is plotted against the time in hours it will form an ascending straight line. That is why it is called the logarithmic phase. This phase is affected by the nature of the organism and the suitability of the environmental conditions as nutrition, pH and temperature. After a certain period, the logarithmic phase merges into the third or stationary phase. In vivo, this phase corresponds to the acute phase of the disease. 3.Stationary phase: During this phase, the rate of growth declines due to exhaustion of food, accumulation of metabolic products and O2 starvation and any bacterial multiplication is balanced by 2023/2024 2023/2024 2023/2024 an increased death rate and the number of living organisms remains constant. During this phase in vivo clinical signs and symptoms of the disease are still present. 4.Decline phase: The number of living organis4ms decreases until all are dead and the culture becomes sterile. This phase corresponds in vivo to the convalescent phase which ends with complete cure. 16  Chapter 3 ‫ﺣﺒﻴﺒﻪ ﺣﺎﻣﺪ ﻣﺤﻤﺪ ﺳﻠﻴﻤﺎﻥ ﺍﻟﺸﺮﻣﻪ‬ Antimicrobial Chemotherapy Definition: A substance, either synthetic or naturally occurring that kills or inhibits the growth of microorganisms such as bacteria, fungi, viruses or other microbes in concentration which is not toxic to the host cells (selective toxicity). Factors determine the effectiveness of antimicrobial agents: 2023/2024 2023/2024 2023/2024 1-The drug should be: Low in toxicity to the host cells while killing the organism. Reach the site of infection. 2-The host should not: Become allergic or hypersensitive to it. Destroy, neutralize or excrete the drug so rapidly. 3- The organism should not readily become resistant to the drug. Classification: The antimicrobial agents include antibacterial, antiviral, antifungal, and antiparasitic agents. 17  A. Antibacterial drugs (antibiotics): Although there are several classification schemes for ‫ﺣﺒﻴﺒﻪ ﺣﺎﻣﺪ ﻣﺤﻤﺪ ﺳﻠﻴﻤﺎﻥ ﺍﻟﺸﺮﻣﻪ‬ antibacterial, the most useful is based on chemical structure. Antibacterial within a structural class will generally show similar patterns of effectiveness, toxicity, and allergic potential. 1. Beta-lactam antibiotics: they all have a beta-lactam ring in their structure. This family includes penicillins, cephalosporins, carbapenems and monobactams, which work by inhibiting the bacterial cell wall synthesis i.e. bactericidal: 2. Quinolones: The quinolones are divided into generations based on their antibacterial 2023/2024 2023/2024 spectrum. The 2023/2024 earlier generation agents are, in general, narrower spectrum than the later ones. The First generation: e.g. nalidixic acid acts on Gram negative bacteria while second generation e.g. ciprofloxacin, norfloxacin and ofloxacin, Third generation e.g. levofloxacin and fourth generation e.g clinafloxacin are broad spectrum. They are bactericidal. 3. Aminoglycosides: such as kanamycin, gentamycin, streptomycin, neomycin, tobramycin and amikacin. They act on aerobic Gram negative bacteria (bactericidal). 4. Sulphonamides/ Folate antagonist: such as sulfacetamide, trimethoprim and co-trimoxazole. They are active against bacteria, chlamydia and rickettsia (bacteriostatic). 5. Tetracyclines: such as tetracycline and oxytetracycine. They are broad-spectrum agents that may be effective 18  against a wide variety of microorganisms, including rickettsia and amebic parasites (bacteriostatic). ‫ﺣﺒﻴﺒﻪ ﺣﺎﻣﺪ ﻣﺤﻤﺪ ﺳﻠﻴﻤﺎﻥ ﺍﻟﺸﺮﻣﻪ‬ 6. Macrolides: such as erythromycin, olendamycin, spectinomycin, azithromycin and clarithyromycin. They act on Gram positive bacteria, mycoplasma, some rickettsia and chlamydia (bacteriostatic). 7. Glycopeptides: such as vancomycin and teicoplanin. Principally effective against Gram positive cocci. Due to their toxicity, their use is restricted to those patients who are critically ill or who have a demonstrated hypersensitivity to the β-lactams (bactericidal). 8. Polypeptides: such as bacitracin (Gram positive bacteria- bactericidal), colistin and 2023/2024 polymyxin B (Gram 2023/2024 2023/2024 negative bacteria- bactericidal). 9. Lincosamides: such as clindamycin and lincomycin (anaerobes, Gram positive bacteria and parasites- bacteriostatic). 10. Nitroimidazoles: such as metronidazole (anaerobic bacteria and parasites). 11. Others: Chloramphenicol, Rifampicin, Isoniazid (INH), Ethambutol, Para-aminosalicylic acid, Nitrofurantoin and Fusidic acid. B. Antiviral drugs: They are a class of medication used specifically for treating viral infections. (See virology) C. Antifungal drugs: They are medications used to treat fungal infections. They include polyenes, azoles and others. D. Antiparasitics: They are a class of medications which are indicated for the treatment of infection by parasites. (See parasitology) 19  Definitions: ‫ﺣﺒﻴﺒﻪ ﺣﺎﻣﺪ ﻣﺤﻤﺪ ﺳﻠﻴﻤﺎﻥ ﺍﻟﺸﺮﻣﻪ‬ Bactericidal antibiotics: Destroy bacteria over a period of hours as penicillins and cephalosporines. Bacteriostatic antibiotics: prevent multiplication of bacteria such as tetracyclines and chloramphenicol. Broad spectrum antibiotics that act on great number of bacteria as broad spectrum penicillins, quinolones, aminoglycosides, choramphenicol and tetracyclines. Narrow spectrum antibiotics are those with selective action as nalidixic acid, macrolides and polypeptides. Mechanism of action of antimicrobial agents (Fig. 9): 1)2023/2024 Inhibition of cell wall synthesis (Bacterial 2023/2024 peptidoglycan) 2023/2024 through: This group of drugs is bactericidal and act only on growing cells (metabolically active cells). 2) Inhibition of cell membrane function: This leads to change the permeability of the cell membrane, causing a leakage of metabolic substrates essential to the life of the microorganism. Their action can be either bacteriostatic or bactericidal. Examples include amphotericin B and polymyxin B. 3) Inhibition of protein synthesis: These drugs interfere with translation of proteins by the ribosome. 4) Inhibition of nucleic acid synthesis: ▪ Interference with DNA replication: as nalidixic acid and nitroimidazole. ▪ Interference with RNA synthesis: as rifampicin and ribavirin. 20  5) Interfere with metabolic processes within the microorganism: ‫ﺣﺒﻴﺒﻪ ﺣﺎﻣﺪ ﻣﺤﻤﺪ ﺳﻠﻴﻤﺎﻥ ﺍﻟﺸﺮﻣﻪ‬ - Sulphonamides and paraaminosalysilic acid (PAS) interfere with folic acid synthesis in bacteria. Mechanisms of antimicrobial drug resistance: 1) Inactivation of antibiotics by production of bacterial enzymes that destroy it: 2) Change in permeability to drug: 3) Alteration (modification) of target sites for antimicrobial action: 4)2023/2024 Altered metabolic pathway other2023/2024 than that inhibited by 2023/2024 the drug: Limitation of drug resistance: 1. Maintain high levels of the drug in the tissue: By adjust dose and course 2. Two drugs given simultaneously: Each of which delays the emergence of mutants resistant to the other drug. 3. Avoid antibiotic abuse : Treat true infection , not colonization or contamination. Use narrow spectrum , leave broad spectrum for severe infections. 4. Do antibiotic sensitivity testing : for proper selection of the appropriate antibiotics. 21 ‫ﺣﺒﻴﺒﻪ ﺣﺎﻣﺪ ﻣﺤﻤﺪ ﺳﻠﻴﻤﺎﻥ ﺍﻟﺸﺮﻣﻪ‬ Complications of antibacterial drugs: 1) Drug resistance due to inadequate or prolonged use. 2) Drug toxicity specially in: Streptomycin→ auditory dysfunction. Chloramphenicol→ Agranulocytosis and aplastic anaemia. 3) Allergic reaction in hypersensitive persons. 4) Early use of drug before proper diagnosis. 2023/2024 2023/2024 2023/2024 → Mask clinical signs and symptoms. → Atypical infection. 5) Early use of drug → suppress formation of antibodies → decrease natural defense → relapses of the disease. 6) Prolonged use → superinfection (suppress of bacterial flora) as: Candida species → colonize mucous membrane causing thrush, in colon (antibiotic associated colitis) after elimination of anaerobic flora. Laboratory tests for antibiotic sensitivity: A physician must know to which antibiotic a particular organism is most sensitive to make a decision concerning the treatment of a patient. 22 ‫ﺣﺒﻴﺒﻪ ﺣﺎﻣﺪ ﻣﺤﻤﺪ ﺳﻠﻴﻤﺎﻥ ﺍﻟﺸﺮﻣﻪ‬ 2023/2024 2023/2024 2023/2024 Fig.(9): Mechanism of action of antimicrobial agents 23  Chapter 4 ‫ﺣﺒﻴﺒﻪ ﺣﺎﻣﺪ ﻣﺤﻤﺪ ﺳﻠﻴﻤﺎﻥ ﺍﻟﺸﺮﻣﻪ‬ Host-Parasite Relationship This chapter will discuss the relationship between the host which is the human body or man and parasites which infect this host e.g. microbes (bacteria, viruses…). Infection: Infection means the invasion of the body of a man or an animal with an infective agent (bacteria, viruses, Rickettsia..). Any disturbance to the physiological functions of the host due to this infection is called infective disease. 2023/2024 2023/2024 2023/2024 Sources of infection: This mean the place or the source from which come this infective microorganism to invade the human body. These sources may be: a- Endogenous. b- Exogenous. a- Endogenous Sources of infection : Endogenous infection may occur from the commensal organisms normally existing in the body which may under certain conditions aquire pathological properties and cause disease (Opportunistic pathogens), e.g.: ▪ E.coli which is a normal commensal in the intestine may cause urinary tract infection if it reaches the urinary system. 24  ▪ Another example is Staph. aureus which may present normally in the nose may also cause a ‫ﺣﺒﻴﺒﻪ ﺣﺎﻣﺪ ﻣﺤﻤﺪ ﺳﻠﻴﻤﺎﻥ ﺍﻟﺸﺮﻣﻪ‬ boil in the skin or infection in a wound. b- Exogenous sources: Here the infection comes from other sources than the patient himself. It may come from: 1- Exogenous human sources. 2- Animals. 3- Arthropods. 4- Inanimate (non living) sources. 1- Exogenous human sources: 2023/2024 2023/2024 2023/2024 a- Patients: Here the infection comes from another ill person as occur in tuberculosis, influenza, syphilis, measles… b- Carriers: A carrier is a person who harbors a pathogenic organism and passes it in his discharge and thus can infect others without himself showing any signs or symptoms of the disease. This may be due to that the organism may cause in such persons what is called subclinical infection which means an infection with small number of the organism which is beyond to give apparent symptoms. The carrier also may be a convalescent carrier. After recovery from the disease they continue to harbor the organism for some time in certain sites. 25  Importance of carriers: Carriers, especially healthy carriers are dangerous ‫ﺣﺒﻴﺒﻪ ﺣﺎﻣﺪ ﻣﺤﻤﺪ ﺳﻠﻴﻤﺎﻥ ﺍﻟﺸﺮﻣﻪ‬ sources of infection because: a- They are not easily detected. b- They are not known to the public. c- They are not confined to bed and thus mix freely with people and transmit the disease from place to place. 2- Animals: Many may be susceptible to some animal diseases where the source of infection to man may come from a diseased animal e.g. anthrax, salmonella food 2023/2024 2023/2024 2023/2024 poisoning, brucellosis, bovine tuberculosis and rabies. 3- Arthropods : Some insects may be a source of infection to man e.g. the mosquitoes in malaria and yellow fever and the ticks in some tick borne diseases. 4- Inanimate sources: The source of infection here is non living source e.g. soil in gas gangrene and tetanus. 26  Methods of transmission and spread of infection : The microorganism may be transmitted from the ‫ﺣﺒﻴﺒﻪ ﺣﺎﻣﺪ ﻣﺤﻤﺪ ﺳﻠﻴﻤﺎﻥ ﺍﻟﺸﺮﻣﻪ‬ source to the susceptible person though several ways: 1- Droplet infection: ▪ As occur in respiratory diseases e.g. influenza, common cold, measles and pneumonia. ▪ The droplets come out through loud talking, sneezing, and coughing and travel less than one meter. 2- Airborne infection : The droplets may dry on the floor to be carried up with dust to be inhaled as in case of 2023/2024 2023/2024 pulmonary T.B. and in 2023/2024 such case they travel more than one meter. 3- Food and drinks (oral route): ▪ Here, pathogenic microbes are discharged in the faeces or urine of infected persons and contaminate food, drinks, or water to be swallowed by another person causing the disease. ▪ Flies play in important role, contaminated hands of food or drink perpetrators e.g. typhoid, cholera, poliomyelitis and food poisoning. 4- Arthropods: Arthropods transmit many infectious diseases: Lice: Transmit epidemic typhus,. Fleas: plague. Mosquitoes: Malaria,. 27  House fly: Usually mechanically either through food contamination from infected stools e.g. enteric fever, cholera, dysentery or contaminating skin causing ‫ﺣﺒﻴﺒﻪ ﺣﺎﻣﺪ ﻣﺤﻤﺪ ﺳﻠﻴﻤﺎﻥ ﺍﻟﺸﺮﻣﻪ‬ wound sepsis or eye causing infections and conjunctivitis. Ticks: Transmit tick-borne relapsing fever. Mites: Transmit scrub typhus. 5- Venereal route: The venereal diseases are transmitted by sexual contact between a diseased person and susceptible another one. AIDS, Syphilis and gonorrhea are known famous venereal diseases. 6- Skin and wounds: 2023/2024 2023/2024 2023/2024 Superficial infections may be acquired by contact with infected hands, clothing or other articles as occur in skin infections, ring worm, tinea infection or after wounding intact skin or mucous membrane which open a pathway for infective organism as staphylococcal and streptococcal infection. 7- Injections: Non disposable common syringes or in blood and plasma transfusion may transmit some disease e.g. AIDS and serum hepatitis. 28  Chapter 5 ‫ﺣﺒﻴﺒﻪ ﺣﺎﻣﺪ ﻣﺤﻤﺪ ﺳﻠﻴﻤﺎﻥ ﺍﻟﺸﺮﻣﻪ‬ Infection and Resistance Infection: As mentioned before, means the invasion of the body of a man or an animal with an infective agent (bacteria, viruses, Rickettsia...). The fate of the organism or the host depends on two important factors: A - The pathogenicity or virulence of the invading organism. 2023/2024 B - The resistance or immunity of the host. 2023/2024 2023/2024 Microbial factors that determine the fate of the infecting organisms o Virulence of infecting organism o The size of the infecting dose o Portal of entry or route of infection o The presence of mixed infection 1- Virulence : Virulence is the power of an organism to invade the tissues, multiply there, and produce serious damage. 29  Virulence factors: A. Adherence factors: ‫ﺣﺒﻴﺒﻪ ﺣﺎﻣﺪ ﻣﺤﻤﺪ ﺳﻠﻴﻤﺎﻥ ﺍﻟﺸﺮﻣﻪ‬ Pili usually help the attachment of the organism on the host cell surface to initiate infection, e.g. N. gonorrhea in genital system and E. coli in urinary system. B. Toxin production: This is because toxins have the ability to destroy tissues. Some organisms are highly toxic e.g. C. tetani which produce very powerful exotoxin destroying the nervous tissue. C. Invasiveness: 2023/2024 2023/2024 2023/2024 This means the ability of the organism to invade and spread in tissue. This is usually accomplished by formation of specific proteins and by production of a group of extracellular enzymes, like: ▪ Collagenase: Which breaks collagen fibres, e.g. Clostridium perfringens (C. perfringens). ▪ Fibrinolysin: Which dissolves fibrin meshwork that limits the spread of infection e.g. Streptococcus pyogenes. ▪ Hyaluronidase: which dissolves hyaluronic acid (the cement like substance between tissues), e.g. Streptococcus pyogenes and Clostridia. D. Presence of capsule: The capsule has repellent action against phagocyte which may engulf the bacteria and stop its spread (e.g. Pneumococci) 30  2- The infection dose: The number of infecting organisms is a very important determining factor in ‫ﺣﺒﻴﺒﻪ ﺣﺎﻣﺪ ﻣﺤﻤﺪ ﺳﻠﻴﻤﺎﻥ ﺍﻟﺸﺮﻣﻪ‬ the production of disease. When the dose is small, the infection organism is usually easily dealt with and is rapidly cleared off by defense mechanisms of the body. When the number is big, the immune mechanisms may fail to cope with the invading organism which multiply in the tissues and eventually cause disease. 3- The route of infection: Usually the quicker the introduction of an organism into the body, the more it is likely to produce a disease. Thus, by the intravenous or intraperitoneal routes a smaller dose 2023/2024 2023/2024 2023/2024 is needed to kill an animal than by the subcutaneous route. Some organisms will be infective only when introduced by special routes, e.g. the influenza or common cold viruses that are infective only via the respiratory tract. 4- Mixed infection: Infection with more than one organism may increase the virulence or invasive power of each other. e.g. H. influenza also potentiates the influenza virus. 31 ‫ﺣﺒﻴﺒﻪ ﺣﺎﻣﺪ ﻣﺤﻤﺪ ﺳﻠﻴﻤﺎﻥ ﺍﻟﺸﺮﻣﻪ‬ Section II :Systemic Bacteriology 2023/2024 2023/2024 2023/2024 32  Chapter (6) ‫ﺣﺒﻴﺒﻪ ﺣﺎﻣﺪ ﻣﺤﻤﺪ ﺳﻠﻴﻤﺎﻥ ﺍﻟﺸﺮﻣﻪ‬ Gram positive Cocci Guide to common Bacteria that infect man Medically Important Bacteria can be divided into six main groups according to their morphology and staining reactions Main groups of pathogenic bacteria Pathogenic Bacteria 1. Gram positive cocci, bacilli and branching bacteria 2023/2024 2023/2024 2023/2024 2. Gram negative cocci, bacilli and coma shaped bacteria 3. Spiral shaped bacteria 4. Acid fast bacteria 5. Cell wall deficient bacteria 6. Obligatory intracellular bacteria 33  Staphylococci Staphylococci are gram positive spherical cells, ‫ﺣﺒﻴﺒﻪ ﺣﺎﻣﺪ ﻣﺤﻤﺪ ﺳﻠﻴﻤﺎﻥ ﺍﻟﺸﺮﻣﻪ‬ arranged in grape like clusters. Some are members of the normal flora of the skin and the mucous membranes of humans especially the nose, others cause abscess formation, a variety of pyogenic infection. The most reliable classification of this genus is according to coagulase test:- 1. Coagulase positive Staphylococci (Staphylococcus aureus). 2. Coagulase negative Staphylococci. Staphylococcus aureus: Is2023/2024 2023/2024 a major pathogen of 2023/2024 humans. NB: Coagulase is an enzyme that clots citrated plasma Staphylococcus aureus Morphology: Staphylococci are gram positive spherical cells arranged in irregular clusters transmitted by contact. Clinical finding: Diseases caused by Staphylococcus aureus are either: 34  ▪ Inflammatory: That are localized pyogenic infection ‫ﺣﺒﻴﺒﻪ ﺣﺎﻣﺪ ﻣﺤﻤﺪ ﺳﻠﻴﻤﺎﻥ ﺍﻟﺸﺮﻣﻪ‬ ▪ Abscess (e.g. dental absess) ▪ Wound infection: Postoperative or following trauma.. a) Toxin mediated: Food poisoning Treatment: Because of the frequency of drug resistance, Staphylococcus isolates should be tested for antimicrobial susceptibility as it maybe MRSA (methicillin resistant Staph aureus) 2023/2024 to help in the choice of treatment. 2023/2024 2023/2024 Streptococci The Streptococci are gram positive spherical bacteria that characteristically forms pairs or chains. Some are members of the normal flora, others are associated with diseases. Group A beta haemolytic streptococci (Streptococcus pyogenes) Morphology: Spherical cocci, Gram positive. They are arranged in chains of variable length transmitted by droplets. Diseases caused by Streptococcus pyogenes: a) Acute follicular tonsillitis which is the most common infection. It presents with high fever and enlarged tender cervical lymph nodes. 35  b) Cellulitis: Is spreading infection of the skin and sub- cutaneous tissues. ‫ﺣﺒﻴﺒﻪ ﺣﺎﻣﺪ ﻣﺤﻤﺪ ﺳﻠﻴﻤﺎﻥ ﺍﻟﺸﺮﻣﻪ‬ c)Toxic infection: Scarlet fever: o Is a droplet infection where there is a sore throat caused by organisms capable of producing the erythrogenic toxin. The disease is characterized by the presence of high fever, red macular rash and sore throat. Treatment: Penicillin is the drug of choice to avoid post- streptococcal diseases. Post-streptococcal diseases 2023/2024 Occurs 1-4 weeks after an acute2023/2024 group A Streptococcal 2023/2024 infection, so they are not attributed to the direct effect of bacteria but to a hypersensitivity response. Rheumatic fever: The disease is preceded by respiratory tract infection. Typical symptoms and signs include fever, malaise, migratory non suppurative arthritis and evidence of inflammation of all parts of the heart. The disease is reactive by recurrent streptococcal infection with more cardiac damage. Prophylaxis: After the first attack of rheumatic fever, patients are protected against recurrence by the use of prophylactic penicillin administration (long acting penicillin) every 3-4 weeks. Alpha (α) haemolytic Streptococci 36  I- Streptococcus viridians o This group is the most prevalent members of the ‫ﺣﺒﻴﺒﻪ ﺣﺎﻣﺪ ﻣﺤﻤﺪ ﺳﻠﻴﻤﺎﻥ ﺍﻟﺸﺮﻣﻪ‬ normal flora of the upper respiratory tract and are important for the healthy state of the mucous membrane occurring in 90% in mouth as normal flora. Sub-acute bacterial endocarditis Streptococcus mutans and others may cause sub- acute bacterial endocarditis. This occurs when Streptococcus viridians reaches the blood stream as a result of trauma in mouth cavity such as a result of tooth extraction. If the heart valves are abnormal as a result of previous 2023/2024 rheumatic affection or2023/2024 due to congenital 2023/2024 abnormalities, bacteria will settle and multiply on heart valves causing endocarditis. The patient is presented by fever, cardiac manifestations and history of cardiac affection. Prophylaxis and treatment: Penicillin must be administrated to patients with history of heart disease before any dental manipulation Streptococcus pneumoniae (Pneumococci) Pneumococci are gram positive cocci that are normal inhabitants of the upper respiratory tract of humans and are important human pathogen. Morphology: Gram positive capsulated , arranged in pairs. The capsule appears as an unstained halo with Gram stain. Diseases caused by pneumococci: pneumonia. 37  Gram-negative Diplococci ‫ﺣﺒﻴﺒﻪ ﺣﺎﻣﺪ ﻣﺤﻤﺪ ﺳﻠﻴﻤﺎﻥ ﺍﻟﺸﺮﻣﻪ‬ Neisseria: ▪ They are G-ve diplococci with adjacent sides concave (kidney or beans shaped). 1. may be pathogenic as N. meningitidis and N. gonorohoea or commensal (most Neisseria species e.g. N. pharyngis ) which are found in throat, Nose ,mouth. 1- Neisseria meningitidis (Meningococci) Morphology: 2023/2024 as mentioned previously. 2023/2024 2023/2024 Pathogenesis: ▪ The organism present in nasopharynx of healthy carriers (Percentage of normal carriers is 5% of population & it reaches 80 – 90% during epidemics). ▪ Source of infection: Case or carrier ▪ Mode of infection: Droplets. ▪ Meningitis: severe headache, projectile vomiting, rigidity of neck, rash & coma and death in severe cases. This tends to occur in epidemic form Sample: blood or CSF. Treatment: 3rd generations cephalosporins e.g. cefotaxime. Prevention&control: 1) Detection of carriers & their treatment: 38  a) Specimen: Nasopharyngeal swab. b) Treatment by rifampicin 600 mg orally twice ‫ﺣﺒﻴﺒﻪ ﺣﺎﻣﺪ ﻣﺤﻤﺪ ﺳﻠﻴﻤﺎﻥ ﺍﻟﺸﺮﻣﻪ‬ daily for 2 days for close contacts as it is excreted in saliva , or ciprofloxacin 500 mg as a single oral dose. (used also as contact chemoprophylaxis) 2) Reduction of personal contact, good ventilation & avoidance of overcrowding. 3) Vaccination: by capsular PLS. of groups A, C, Y & w-135 is available tetravalent vaccine). 2023/2024 2023/2024 2023/2024 2- Neisseria Gonorrhoeae. (Gonococci) Morphology, staining and culture: Characters of N. gonorrhoeae are more or less similar to those of N. meningitidis. Pathogenesis:-  Infection occur mainly by sexual intercourse leading to Gonorrhea  In males: Urethritis with discharge.  In females: Endocervicitis with discharge and infertility.  Non venereal Transmission of N.Gonorrhoeae: 39  1) Gonococcal ophthalmia neonatorum: an infection of eye of newborn during passage ‫ﺣﺒﻴﺒﻪ ﺣﺎﻣﺪ ﻣﺤﻤﺪ ﺳﻠﻴﻤﺎﻥ ﺍﻟﺸﺮﻣﻪ‬ through infected birth canal. 2) Gonococcal vulvovaginitis: from the contaminated clothes or toilet seats Diagnosis: Acute: Specimen: Discharge from male or female Treatment: o Ceftriaxone is the drug of choice. 2023/2024 2023/2024 2023/2024 Prevention: o Prompt treatment of symptomatic patients. o Use of condoms. o Neonatal ophthalmia is prevented by use of erythromycin or tetracycline eye drops or eye ointment immediately after birth. 40  Chapter (8) Mycobacteria ‫ﺣﺒﻴﺒﻪ ﺣﺎﻣﺪ ﻣﺤﻤﺪ ﺳﻠﻴﻤﺎﻥ ﺍﻟﺸﺮﻣﻪ‬ Definition: The Mycobacteria are rod- shaped strict aerobic bacteria which are difficult to stain with the normal dyes due to high lipoidal content at their cell wall. Classification: It is convenient to divide Mycobacteria of clinical interest into: 1) Mycobacterium tuberculosis complex (MTC): The most important species of this group are M. tuberculosis that infects only man and M. bovis that 2023/2024 infect both man and cattle. 2023/2024 2023/2024 2) Mycobacterium leprae: that causes leprosy in man. Mycobacterium tuberculosis and Mycobacterium bovis Morphology and staining: They are bacilli. Stained by Zeihl- Neelsen technique of staining. They appear as pink rods, against blue background. Mode of infection: Airborne infection: Inhalation of an aerosol containing TB. Ingestion: consumption of infected milk or meat of cows. 41  Tuberculosis in man ‫ﺣﺒﻴﺒﻪ ﺣﺎﻣﺪ ﻣﺤﻤﺪ ﺳﻠﻴﻤﺎﻥ ﺍﻟﺸﺮﻣﻪ‬ It commonly affect lung , but affect also lymph nodes , intestine, bone, CNS , kidney and other parts of the body. Vaccination:  BCG vaccine  Intradermal injection in 3 months age infant.  Indications: - Children. 2023/2024 2023/2024 2023/2024 - Health Care Workers. According to settings in which a high percentage of TB patients  The aim of BCG vaccination is to prevent serious form of primary TB as meningitis and systemic TB  Contraindications: - Immunosuppression. e.g: HIV infected, organ transplant) as it is live attenuated. - Pregnancy. Treatment: Treatment of TB needs: Special drug for TB (e.g. INH), many drugs must be used (at least three drugs) to prevent emergence of drug resistant mutants, for Long period (6-9 months at least). Treatment through DOTS regimen (Direct observed Treatment of Short Course) Mycobacterium leprae 42  M. lepra is the causative organism of leprosy. The organism multiplies in the cooler parts of the body mostly the skin with predilection of peripheral nerves. So, the ‫ﺣﺒﻴﺒﻪ ﺣﺎﻣﺪ ﻣﺤﻤﺪ ﺳﻠﻴﻤﺎﻥ ﺍﻟﺸﺮﻣﻪ‬ peripheral manifestations of the disease are skin lesions, peripheral neuropathy with peripheral nerve thickness. It leads to severe deformities like losing fingers and nose.It has similar morphology to TB.Infection is by inhalation and needs close contact with patient for long time. Diagnosis : ZN stained smears from nasal mucosa and skin lesions Prevention and control: lepromatous patients are segregated in closed colonies for treatment and limitation of spread of infection. 2023/2024 2023/2024 2023/2024 Chemoprophylaxis for the family contacts. Treatment: Dapson. 43  Chapter (9) Gram-negative bacilli ‫ﺣﺒﻴﺒﻪ ﺣﺎﻣﺪ ﻣﺤﻤﺪ ﺳﻠﻴﻤﺎﻥ ﺍﻟﺸﺮﻣﻪ‬ Family Enterobacteriaceae The family Enterobacteriaceae comprises numerous related organisms with common criteria; All of which are: ▪ Found mainly in the colon, many as part of the normal flora. The pathogenic genera are the Shigella, and Salmonella. ▪ They are gram negative bacilli. Escherichia coli These are normal inhabitants 2023/2024 2023/2024of the intestine; 2023/2024 however, some can cause disease in man. It is the commenst cause of urinary tract infection and transmitted by contact. Klebsiella They are normal inhabitants of the intestine. It can cause pneumonia and urinary tract infection and transmitted by contact. Non-Lactose Fermenters Salmonella Salmonellae are intestinal pathogens causing enteric fever (Typhoid fever) Enteric Fever o Mode and source of infection: The organism from the stool of a case or carrier contaminates foods or drinks. 44  o Clinical picture:  Fever, Tender spleen, constipation and rose ‫ﺣﺒﻴﺒﻪ ﺣﺎﻣﺪ ﻣﺤﻤﺪ ﺳﻠﻴﻤﺎﻥ ﺍﻟﺸﺮﻣﻪ‬ spots on the abdomen. Treatment: ofloxacin (Tarivid) is used. Prevention : examination and education of foodhandlers Vaccine Shigella They are intestinal pathogen, where they produce bacillary 2023/2024 dysentery. 2023/2024 2023/2024 bacillary dysentery Source of infection: is a case or carrier. Mode of transmission: ingestion of contaminated food or water. Clinical picture: Abdominal pain, tenesmus with the passage of frequent stools composed of mucus and blood. Treatment: o Main treatment is the restoration of fluid and electrolyte balance. o Antibiotic sensitivity tests should be done. 45  Pseudomonas Pseudomonas aeruginosa (Pseudomonas ‫ﺣﺒﻴﺒﻪ ﺣﺎﻣﺪ ﻣﺤﻤﺪ ﺳﻠﻴﻤﺎﻥ ﺍﻟﺸﺮﻣﻪ‬ pyocyanea) Ps. aeruginosa is commonly present in the moist environments in hospitals.. Morphology: Gram negative bacilli. Pathogenicity: o The organisms occur naturally in the intestine and on the skin and these sites constitute the source of infection. o If immunity decreases, it may cause urinary tract infection, infected wounds and 2023/2024 burns. Infection is 2023/2024 2023/2024 associated with greenish blue pus. o It causes 10-20% of hospital acquired infections. It is highly resistant to antibiotics and transmitted by contact.. 46  Vibrios These are gram negative thin curved or comma ‫ﺣﺒﻴﺒﻪ ﺣﺎﻣﺪ ﻣﺤﻤﺪ ﺳﻠﻴﻤﺎﻥ ﺍﻟﺸﺮﻣﻪ‬ shaped bacilli motile by terminal flagella. Vibrio cholera This is the causative organism of asciatic cholera. Morphology: Typical morphology of Vibrios. Cholera (Asciatic cholera) Cholera is typically characterized by sudden onset of nausea, vomiting and rice watery diarrhea, abdominal cramps and hypovoleamic shock. Many patients (20-30%) die within 2 days. 2023/2024 2023/2024 2023/2024 The source of infection: faces of a case or carrier. Mode of transmission: ingestion of contaminated food or water. Treatment: 1. Correction of fluid and electrolyte imbalance. 2. Antibiotics; tetracycline is the drug of choice for cases and carriers. 47  Chapter ( 9 ) ‫ﺣﺒﻴﺒﻪ ﺣﺎﻣﺪ ﻣﺤﻤﺪ ﺳﻠﻴﻤﺎﻥ ﺍﻟﺸﺮﻣﻪ‬ G +ve bacilli: (1) Aerobic non sporing :Corynebacterium diphtheria Morphology: These are Gram positive rods arranged at obtuse angles giving Chinese letter appearance Pathogenesis: Virulence of diphtheria bacilli is due to exotoxin which is effectively absorbed and is active on a range of tissues including 2023/2024 heart muscles and peripheral nerves. 2023/2024 2023/2024 ▪ Diphtheria is a disease that affects children and sometimes adults. ▪ Infection spreads by droplet or contact from a case or a carrier. Tonsillar Diphtheria: The initial lesion usually occurs on the tonsils and oropharynx. It may spread to nasopharynx larynx and trachea. The organism multiplies rapidly on the epithelial cells in the local lesion and produces an exotoxin that causes necrosis of cells in the area. Later a very tough adherent pseudomembrane. The bacilli in the pseudo membrane continue to multiply and produce toxin, which is effectively absorbed to produce distant toxic damage to heart muscles. Regional lymph nodes in the neck are enlarged with possible marked oedema of the entire neck. 48  Nerves may also be damaged resulting in paralysis of the soft palate, eye muscles or even extremities. ‫ﺣﺒﻴﺒﻪ ﺣﺎﻣﺪ ﻣﺤﻤﺪ ﺳﻠﻴﻤﺎﻥ ﺍﻟﺸﺮﻣﻪ‬ Treatment: 1. Antitoxin: diphtheria antitoxin is considered the only specific and effective treatment. It should be given as soon as clinical diagnosis is established even without waiting for laboratory confirmation. 2. Chemotherapy: Penicillin G is the drug of choice. 2023/2024 2023/2024 2023/2024 Prophylaxis: Active Immunization: - toxoid: Three injections commonly combined with DPT vaccine. Given intramuscularly to children at the age of 2, 4 and 6 months of age. A booster dose is required a year later and another at school age. 2) Aerobic spore-bearers The bacillus group This genus is characterized by being gram positive spore forming bacilli which can be used in the biological terrorism. (Bacillus anthracis) Morphology: 49  Gram positive bacilli, arranged in chains. They are capsulated in vivo. They form spores in vitro. Spores are central, ovoid and are not stained with Gram. ‫ﺣﺒﻴﺒﻪ ﺣﺎﻣﺪ ﻣﺤﻤﺪ ﺳﻠﻴﻤﺎﻥ ﺍﻟﺸﺮﻣﻪ‬ Pathogenesis and mode of infection: Anthrax is primarily a disease of herbivores animals (zoonotic disease). Humans are infected by contact with infected animals or by contact with animal products. Anthrax in man occurs in three clinical forms: 1. Cutaneous anthrax (Malignant pustule). 2. Pulmonary anthrax (wool sorter’s disease) N.B: The high death rate, spore persistence and restriction of infection to those exposed to it make anthrax an attractive bioweapon. 2023/2024 2023/2024 2023/2024 Chapter (10) Anaerobic spore-bearers Genus Clostridium Clostridium tetani It is the causative organism of tetanus in humans and animals. The disease is nowadays uncommon in the developed countries as a result of active immunization programmes. The organism is worldwide distributed in the soil and feces of horses and other animals. Morphology: Gram positive rods. The spore is terminal and spherical with drum stick appearance. 50  Virulence factors and pathogenicity: ‫ﺣﺒﻴﺒﻪ ﺣﺎﻣﺪ ﻣﺤﻤﺪ ﺳﻠﻴﻤﺎﻥ ﺍﻟﺸﺮﻣﻪ‬ Cl. tetani has little or no invasive power. It owes its pathogenecity to the production of a powerful exotoxin having particular affinities for the anterior horn cells of the spinal cord.