Pa Tho Genesis Of Bacterial Infection

PATHOGENESIS OF BACTERIAL INFECTION (from Dr. Lagamayo’s ppt) • initiation of infectious process • mechanisms that lead to the development of signs and symptoms of disease CHARACTERISTICS OF PATHOGENIC BACTERIA: • Transmissibility • Adherence to host cells • Invasion of host cells and tissues • Toxigenicity • Ability to evade the host’s immune system (“escape mechanisms) Definition of Terms: 1. Adherence (adhesion, attachment) – process by w/c bacteria stick to the host cell surfaces 2. Carrier – a person or animal with asymptomatic infection that can be transmitted to another susceptible person or animal 3. Infection – multiplication of an infectious agent within the body 4. Invasion – a process whereby bacteria, animal parasites, fungi, and viruses enter host cells or tissues and spread in the body 5. Nonpathogen – microorganism that does not cause disease (normal flora) 6. Opportunistic pathogen – capable of causing disease only when host’s resistance is impaired Ex. E.coli, Pseudomonas spp., Stenotrophomona maltophilia 7. Pathogen – capable of causing disease Ex. Mycobacterium tuberculosis, Yersinia pestis 8. Pathogenicity – ability to cause disease 9. Toxigenicity – produce toxin that contributes to the development of disease 10. Virulence – quantitative ability of an agent to cause disease Other Epidemiologic Terms: 1. Etiologic agent - microorganism responsible for causing infection or disease 2. Common source – etiologic agent responsible for an epidemic or outbreak, originates from a single source or reservoir 3. Incidence – number of diseased or infected persons in a population 4. Prevalence - % diseased in a given pop’n at a given time 5. Endemic – disease constantly present at some rate of occurrence in a particular location 6. Epidemic – larger than normal number of diseased in a particular region 7. Pandemic – epidemic spanning the world 8. Outbreak – larger than normal number of diseased that occurs over a relatively short period of time 9. Nosocomial infection – infection acquired from hospital 10. Strain typing – relatedness of organisms to one another during a particular outbreak or epidemic 11. Surveillance – epidemiologic investigation 12. Vector – carrier of etiologic agent 13. Vehicle – non-living entity contaminated by etiologic agent Koch’s Postulate

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The microorganism should be found in all cases of the disease in question, and its distribution in the body should be in accordance with the lesions observed The microorganisms should be grown in pure culture in vitro for several generations When such pure culture is inoculated into susceptible animal species, the typical disease must result The microorganism must again be isolated from such experimentally produced disease

*Organisms that do not meet Koch’s postulate: o Cannot be grown in culture, only in animal model: Treponema pallidum (syphilis) Mycobacterium leprae (leprosy) o Can be grown only in culture: Neisseria gonorrhea (gonorrhea) Molecular Koch’s Postulate • study of genes assoc. with virulence • PCR – used to amplify microorganismspecific nucleic acid sequences

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Ex. Whipple’s disease (Tropheryma whipplei), Bacillary angiomatosis (Bartonella henselae), Human monocytic ehrfichiosis (Ehrlichia chaffeensis), Hantavirus pulmonary syndrome (Sin Nombre virus), Kaposi’s sarcoma (human herpes virus 8)

Molecular Koch’s Postulate 1. Phenotype or property under investigation should be significantly associated with pathogenic strains of a species and not with nonpathogenic strains 2. Specific activation of the genes assoc with the suspected virulence trait should lead to measurable decrease in pathogenicity or virulence 3. Reversion or replacement of the mutated gene with the wild-type gene should lead to restoration of pathogenicity or virulence.

MOLECULAR GUIDELINES FOR ESTABLISHING MICROBIAL DISEASE CAUSATION: 1. Nucleic acid sequence of a putative pathogens should be present in most cases of an infectious disease 2. Nucleic acid sequence of a putative pathogen should be absent from most healthy controls. If ever, it should be present in lower copy numbers 3. Copy number of pathogen-assoc. nuclei acid sequence should decrease or become undetectable with resolution of the disease and should increase with relapse or recurrence of disease 4. The presence of pathogen-assoc. nucleic acid sequence in healthy subjects should help predict the subsequent development of disease 5. The nature of pathogen inferred from phylogenetic analysis of its nucleic acid sequence should be consistent with the known biologic characteristics of closely related organisms and the nature of the disease 6. A dose-response relationship between pathogen-associated nucleic acid sequence and pathology should be evident 7. The sequence-based findings should be reproducible

Prodromal stage

TRANSMISSION OF INFECTION

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Bacteria adapt to the environment to: o ensure their survival o enhance the possibility of transmission – asymptomatic infection or mild disease (Ex. Hepa B) Some bacteria exist primarily in animals and incidentally infect humans o Salmonella in eggs and Campylobacter in milk) Some bacteria produce inadvertent infection of humans o Yersinia pestis causing plague o Bacillus anthracis causes anthrax – lives in the environment, occasionally infects animals transmitted to humans by contaminated raw hair Inadvertent infections o Clostridium spp. – ubiquitous in the environment and are transmitted to humans by ingestion (C. perfringens & C. botulinum) or when wounds are contaminated by soil (C. perfringens & C. tetani) Disease manifestations of microorganisms often promote transmission of these agents o Vibrio cholerae, E. coli (diarrhea), Mycobacterium tuberculosis (cough)

TRANSMISSION OF INFECTION IN HUMANS • Person to person contact through hands (nosocomial infections) Ex. Staphylococcus aureus • Most common portals of entry (mucous membrane with the skin) o Respiratory tract (upper and lower) o GI tract o Genitourinary tract • Cuts, burns, injuries INFECTIOUS PROCESS *Streptococcus pneumoniae in the nasopharynx may be aspirated into the lungs (aspiration pneumonia) resulting in bacteremia in 10-20% of individuals affecting the CSF (meninges), heart valves and joint spaces HOST-MICROORGANISM INTERACTIONS Encounter and entry Pathogen encounters and colonizes host surface

Colonization and entry Pathogen multiplies and breaches host surface defenses

Invasion and dissemination Pathogen invades deeper tissues and disseminates, encounters inflammatory and immune responses

Outcome Pathogen completes cycle: - leaves host - destroys host - remains in latent state - is destroyed by host

INFECTION-DISEASE STAGES Incubation stage No signs or symptoms

First signs and symptoms Pathogen may be highly communicable

Clinical stage Peak of characteristic signs and symptoms of infection or disease

Stage of decline Condition of host deteriorates possibly to death or signs and symptoms begin to subside as host condition improves

Convalescent stage Full recovery of surviving host or chronic infection develops or death

SIGNS AND SYMPTOMS OF INFECTION & INFECTIOUS DISEASE •

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General or localized aches and pains Headaches and fever Swollen lymph nodes Rashes Redness and swelling Cough and sneezes Congestion of nasal and sinus passages Sore throat Nausea and vomiting Diarrhea

MICROBIAL STRATEGIES FOR SURVIVING INFLAMMATION • Avoid killing by phagocytes (PMNs, Monocytes and Macrophages) o Inhibit ability of phagocyte to ingest by producing capsule o Avoid phagocyte mediated killing by:  Inhibiting phagosome lysosome fusion  Being resistant to destructive agents (ex. Lysozyme released by lysosomes)  Actively and rapidly multiplying within the phagocyte • Avoid effects of the complement system o Use capsule to hide surface molecules that would otherwise activate the complement system o Produce substances that inhibit the processes involved in complement activation o Produce substances that destroy specific complement proteins MICROBIAL STRATEGIES FOR SURVIVING THE IMMUNE SYSTEM • Pathogen multiplies and invades so quickly that damage to host is complete before immune response can be fully activated (influenza) • Pathogen invades and destroys cells involved in the immune response (HIV) • Pathogen survives, unrecognized, in host cells and avoids detection by immune system • Pathogen covers its antigens with a capsule so that immune response is not activated • Pathogen changes antigens so that immune system is constantly fighting a primary encounter • Pathogen produces enzymes (proteases) that directly destroy or inactivate antibodies.

CLONAL NATURE OF BACTERIAL PATHOGENS • Primary mechanism for exchange of genetic info between bacteria: plasmids or phages • Clonality of organisms: o Result of conservation of chromosomal genes in bacteria o One or a few clonal types of organism spread in the world during a period of time (epidemic) o Examples:  Serogroup A meningococcoal meningitis in Asia, Middle East, and Africa

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H. influenzae type b Two clonal types of Bordetella pertussis and Salmonella typhi assoc with disease

BACTERIA VIRULENCE FACTORS A. adherence factors B. toxins C. enzymes D. antiphagocytic Factors E. intracellular pathogenicity F. antigenic heterogeneity

A. Adherence Factors • Surface hydrophobicity • Net surface charge • Host cell receptor interactions *Hydrophobicity of bacterial cell surface is directly proportional to the adherence to the host cell Pili – hair like appendages that extend from bacterial surface Examples: 1. E. coli strains have 1 pilus which adhere to epithelial receptors containing D-mannose > adherence can be blocked in vitro by adding D-mannose to the medium 2. E. coli causing UTI have P pili which attach to a portion of P-blood group Ag(α-D-galatopyranosyl(1-4)-β –D-galactopyranoside [GAL-GAL binding adhesion} 3. Streptococcus pyogenes (Group A strep) have fimbriae > Fimbriae – lipoteichoic acid, Protein F, Protein M > Protein F and lipoteichoic acid- adherence to buccal epithelial cells > Fibronectin – act as host cell receptor molecule > M protein – anti-phagocytic molecule B. Toxins Classification of toxins: 1. Exotoxin – V. cholerae, S. aureus (enterotoxin), V.parahemolyticus, C. perfringens, C. Botulinum 2. Endotoxin – GND (Enterobacteriaceae) - lipopolysaccharide (LPS) 3 main regions : • O-specific polysaccharide • Common core polysaccharide • Lipid A with KDO (2-keto-3deoxyoctonic acid) - lipooligosaccharide - heat stable *peptidoglycan of gram positive bacteria causes vascular damage leading to shock Exotoxin

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Excreted by living cells; ↑ conc. in liquid medium Most commonly associated with gram positive bacteria Unstable, destroyed at temp. > 60˚ C Highly antigenic Converted to antigenic non-toxic toxoids by formalin, acid, heat etc. (for vaccines ex. Tetanus) Highly toxic; fatal Specific receptors Does not produce fever Controlled by extrachromosomal components (ex. plasmids)

Endotoxin • Released on bacterial death • Integral in gram negative bacteria • Composed of lipopolysaccharide complexes (LPS portion of cell envelope)

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Stable; withstands heat at temp. >60˚ C • Weakly immunogenic • Not converted to toxoids • Moderately toxic • Specific receptors not found on cells • Produces fever (triggers release of IL-1) • Synthesis directed by chromosomal genes *Effects on host: o Disseminated intravascular coagulation o Fever o Activation of complement and immune systems o Circulatory changes that lead to hypotension, shock and death C. Enzymes 1. Tissue degrading enzymes Lecithinase – C. perfringens Collagenase – C. perfringens Hyaluronidase – Staph., Strep., anaerobes Coagulase – S. aureus Streptolysin O, S Cytolysins: leucocidins, hemolysins 2. IgA1 proteases N. gonorrhea N. meningitides H. influenza S. pneumoniae

D. Antiphagocytic factors

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Protein A of Staphylococcus aureus binds to Fc portion of IgG Ex. Streptococcus pneumoniae N. meningitides S. pyogenes (M protein) N. gonorrhea (pili)

E. Intracellular pathogenicity • Mechanisms: 1. avoid entry into phagolysosomes and live within the cytosol of phagocytes 2. prevent phagosome-lysosome fusion and live within the phagosome 3. resistance to lysosomal enzymes and survive within the phagolysosome

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Ex. Mycobacterium tuberculosis Brucella spp. Legionella spp.

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symptomatic sore throat even when the C. diphtheria strains are nontoxigenic 2. Shigella sp. Adhere to host cells in vitro (HeLa cells- undifferentiated unpolarized cells from cervical CA) *adherence causes actin polymerization in the nearby HeLa cells  pseudopod formation engulfment of bacteria *In vivo Shigella adhere to integrins on the surface of M cells in Peyer parches. M cells sample antigens and present them to macrophages in the submucosa. Shigella are phagocytosed by M cells, pass through M cells, escape killing by macrophages Ex. Yersinia enterocolitica, Listeria monocytogenes 3. Legionella pneumophilia adherence to macrophage formation of thin, long pseudopod which coils around the bacteria forming a vesicle (coiling phagocytosis) bacteria multiplies within the vesicle 4. Neisseria gonorrhea pili (primary adhesions) opacity associated proteins (Opa) - secondary adhesions to host cells - some Opa mediates adherence to PMNs

Inside PMN cells, macrophages or monocytes

F. Antigenic heterogeneity (surface structures) • The antigenic type of bacteria may be a marker of virulence • Examples: o V. cholerae O antigen type 1 and O antigen type 139 – produce cholera toxin o ≥80 group A streptococcal M protein types – high incidence of post strep. glomerulonephritis o N. meningitides capsular polysaccharide types A & C area associated with epidemic meningitis o Borrelia recurrentis (relapsing fever)

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N. gonorrhea – 3 surface- exposed antigens that switches forms at a high rate (LOS, pili, Opa(protein II))

REGULATION OF BACTERIAL VIRULENCE FACTORS Corynebacterium diptheriae o The gene for diphtheria toxin is carried on temperate bacteriophage o Toxin produced only by strains lysogenized by the phages o Enhanced toxin production with low iron medium Bordetella pertussis o Expression of virulence genes is enhanced when grown at 37˚ C and suppressed when grown at lower temp o In the presence of high concentrations of Mg sulfate or nicotinic acid

THE REQUIREMENT FOR IRON

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Vibrio cholerae o Expression of cholera toxin: -higher at pH 6.0 than pH 8.5 - higher at 30˚ C than at 37˚ C Yersinia pestis o YOPS – series of yersinia virulence plasmid-encoded proteins with antiphagocytic function o Expressed maximally at 37˚ C in the absence of calcium Yersinia enterocolitica o Motile at 25˚ C, non motile at 37˚ C Listeria monocytogenes o Motility enables the bacteria to spread and multiply in the environment or in the patient INVASION OF HOST CELLS and TISSUES • Invasion – entry of bacteria into the host cells - many bacteria produce virulence factors that influence the host cells •

Toxin production and other virulence properties are generally independent of the ability of bacteria to invade cells and tissues.

Examples: 1. Corynebacterium diphtheria can invade the epithelium of nasopharynx and cause

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Bacteria require 0.4-4μmol of iron in order to grow Siderophores (MW 500-1000): o Small ligands that are specific for ferric iron and supply iron to the bacterial cells o Capture iron o Produced only under low iron conditions o 2 Categories: a. Catechols (phenolates) Ex. enterobactin – used Enterobacteriaceae -remove iron from transferring b. Hydroxamates – found in fungi Ex. Ferrichrome The availability of iron affects the virulence of pathogens N. meningitidis – virulence for mice in increased ≥1000 fold when the bacteria is exposed under iron-limited conditions

ROLE OF BACTERIAL BIOFILMS Biofilm • aggregate of interactive bacteria attached to a solid surface or to each other, encased in an exopolysaccharide matrix • forms slimy coat on solid surfaces and occurs throughout nature Human infections associated with biofilm: • Staph. epidermidis & Staph. Aureus - central venous catheters - eye infections (contact and intraocular lenses) - dental plaque • Pseudomonas aeruginosa - airway infections in cystic fibrosis

Biofilm formation Colonization of the surface (flagella, pili, cell division) Quorum sensing signals (acylhomoserin e lactose signals) α to number of

Bacterial change in behavior (changing activation of genes) *extracellular polysaccharide production *alginate production by P. pseudomonas *genes influence metabolic pathway *production of virulence factors *antimicrobial resistance (diffusion border)

Sarah 07/14/06