Bacteria Pathogenesis Lecture PDF

‫كلية التقنية الطبية جامعة طرابلس‬ Microbiology Bacterial pathogenesis Lecture Present by : Najla Elyounsi Msc in medical laboratory.science 1 8/1/2025Wednesday 2 8/1/2025Wednesday  Pathogen: microbe has...

‫كلية التقنية الطبية جامعة طرابلس‬ Microbiology Bacterial pathogenesis Lecture Present by : Najla Elyounsi Msc in medical laboratory.science 1 8/1/2025Wednesday 2 8/1/2025Wednesday  Pathogen: microbe has ability to causing infection, some microbes are.highly pathogenic, whereas others cause disease rarely (low pathogenic) Virulence: it is referred to degree of ability of microbe to produce disease. The virulence is determined by virulence factors such as capsule enzymes and toxins. Commensal : (normal flora ) are those of bacteria that reside on either surface of the body or mucosa without harming human healthy. Some of them are protecting from various pathogenic bacteria. (E. coli) Opportunistic bacteria that normally do not cause disease but become pathogenic when the body's defense system is impaired Infection, in general, is presence and multiplication of microbe within human body, and cause infectious disease Disease 3 : occur if the infection lead to a pathological 8/1/2025Wednesday  :Characters of pathogen A-Pathogenic organism should be able to enter the host body B-Pathogenic organism should be able to multiply in tissue. C-Pathogenic organism should be able to damage the tissue. D -They must be capable to resist the host defense. Virulence factors of pathogen Some important virulence factors that have role in pathogenesis of bacteria: Capsule: 1.Which mediate adherence of pathogen to specific receptors on host cell surface. 2.Prevent the phagocytes from adhering to bacteria, therefore act as anti phagocytic factor. Pili: 1.Which mediate adherence to specific sites on surface of host cell. 4 8/1/2025Wednesday ymes everal enzymes secreted by bacteria play role in pathogenes ns : bacteria produce two:Sources types of of infection toxins; exotoxin and endotoxin Human: is common source of infection from patients or carriers. Fomites are inanimate objects of patients that serve as source of organism. Animals; are important source of organisms that infect human, the organisms can transmitted from infected animals to human and cause disease. The disease is called zoonosis. Soil; may serves as source of infection for many pathogenic organisms or spores of some bacteria and fungi. Food; contaminated food may be source of infection, eg. 5 Staphylococcal food poisoning. 8/1/2025Wednesday  :Stages of bacterial pathogenesis 1.Transmission and portal of entry: A-Portals of entry(routes of infection):four important portals of entry 1.Respiratory tract. 1.Alimentaryy tract. 2.Skin 4.Genital tract 6 8/1/2025Wednesday B-Mode of transmission Inhalation: the bacteria may be transmitted by inhalation of respiratory secretions of infected patients or by inhalation of contaminated dust with bacteria (from soil). Ingestion: the bacteria can be transmitted by consumption of contaminated water or food. Skin contact: bite, wound: The transmission may occur through skin contact or can be occurs by trauma. The transmission from animal to human can take place either directly from bite of reservoir animal host; or indirectly through the bite of insect vectors. Those bacteria may be introduced directly into blood stream or remain at site of infection. Blood transfusion: some bacteria can be transmitted by blood transfusion. Injection of needles during intravenous drug use or indwelling catheter, have role in transmission. Sexual : intercourse: certain bacteria can be transmitted by sexual contact 7 8/1/2025Wednesday.All above methods are called horizontal transmission Trans-placental; the infection of fetus can occur between mother and offspring across the placenta, at time of delivery, or during breast feeding. The transmission from mother to her fetus is called Vertical transmission. 8 8/1/2025Wednesday dherence and-2 multiplication Certain bacteria have specialized structures (adherence factors, such as pili and capsule) which allow them to adhere to specific sites on surface of human cell, thereby enhancing their ability to cause diseases. The bacteria can be multiplied by growth at site of adherence and form colonization, or spread to another tissues by invasion. 9 8/1/2025Wednesday Invasion and damage of host.3 :tissues The invasion is ability of — microorganism to spread into host tissues, some bacteria are non invasive, but multiply at site of adherence. Bacteria secrete several invasive factors that play role in pathogen :a. Enzymes Collaginase and hyaluronidase ;.1 which degrade collagen and hyaluronic 10 8/1/2025Wednesday acid ,thereby allowing the bacteria to Coagulase: which accelerates the.2 formation of fibrin clot from fibrinogen around bacteria to protect the bacteria.from phagocytosis action fibrinogen--Coagulase --fibrin IgA protease: which degrades this.3 immunoglobulin; allowing the bacteria to adhere to mucous membrane leucocidin: which can destroy both.4.neutrophile and macrophages Hemolysin: which can destroy RBC.5 Capsule: prevent the phagocytes.6 from adhering to bacteria therefore, 11 8/1/2025Wednesday  :b. Toxin production The bacteria produce two types of toxins,.exotoxin and endotoxin Exotoxin is produce by G+ ve and G- ve ,bacteria. In contrast Endotoxin : which is produce by only G- ve bacteria. Exotoxin is protein, whereas.endotoxin is lipid and carbohydrate Exotoxin is good antigen and induce high titer of antibody (antitoxin), whereas endotoxin is weakly antigenic and not induce antitoxin. exotoxin is heat labile at 60C, when treated with formaldehyde (or acid or heat) can be converted in toxoid (the toxin is lost their toxicity but retain their 12 antigenicity, therefore can be used as 8/1/2025Wednesday 13 8/1/2025Wednesday  Exotoxins Endotoxin Relation to bacteria Excreted by living Released usually when cell cell lysed Part of outer membrane Nature protein substance Lipopolysaccharide (lipid A ) Bacteria 8. G- and G+ bacteria G- bacteria Immunological Identification Toxicity high toxic Low toxic Stability Unstable heat labile Heat stable (60°C) often (autoclaving 121°C destroyed by heating for one hour at above (60°C) Immunogenic Highly Immunogenic Weakly Immunogenic 14 8/1/2025Wednesday Gene site Plasmid Chromosome  Mechanisms for escaping host defense (evasion) There are many difference way of evading or.subverting the immune response Phagosytosis.1 For organisms that are internalized they- generally choose three strategies to avoid. intercellular killing Some bacteria resist phagocytic destruction by- preventing fusion of the lysosome with the.phagosome Some bacteria resist phagocytic destruction by- escaping from the phagosome before the.lysosome 15 fuses 8/1/2025Wednesday Bacterial surface modulators (capsule) -2 It is a common mechanism of masking bacterial surfaces is to express a carbohydrate capsule, which relies extensively on its capsule to prevent antibody and complement deposition on its surface, thereby avoiding opsonization and phagocytic clearance (increase the virulence of many pathogenesis) Antigenic variation -3 Antigenic variation is a major mechanism of passively evading the host immune surveillance. Antigenic variation is a process where in a pathogen modifies its surface antigens (proteins) , aiming to avoid immunological recognition by the.host 16 8/1/2025Wednesday 17 8/1/2025Wednesday