Chapt 25 Lecture- Microbial Pathogenisis
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61 terms
Terms | Definitions |
|---|---|
 Infection | entry of pathogen or parasite (doesnt always cause disease- most infections are removed by immune system) |
| Primary pathogens | have ability to penetrate host defenses |
| Opportunistic pathogens | cause disease only in compromised host (weakened immune system) (break in tissue allows organisms access to new site) (loss of other microflora allows organisms to bloom) |
| Pathogenicity of organism | measure of ability to cause disease- determined by genetic makeup of organism |
| Infectious dose | ID50 number of organisms to colonize 50% of hosts |
| Virulence | rate of lethal infections Lethal dose = LD50 |
| Lethal dose = LD50 | number of organisms to kill 50% of hosts |
| Infection cycle | spread by: direct contact - body fluids indirect contact |
| Spread by indirect contact | contact with fomite - inanimate objects or substances that can carry infectious microbes (eg. door knobs) |
| Spread by indirect contact | Horizontal transmission via vectors eg. mosquitos - yellow fever, malaria, West Nile virus mosquito may not show symptoms of those diseases however |
| Mode of entry of pathogen | mucosal surface, wounds, insect bites |
| VIRULENCE FACTORS: virulence genes | Virulence genes encode factors that allow pathogen to iINVADE host |
| Examples of virulence factors | toxins attachment proteins capsules |
| Pathogenicity islands | section of genome - contains multiple virulence genes that code for related function |
| How are pathogenicity islands transferred? | As a block from one organism to another |
| Virulence Factor definition | structure and characteristics of pathogens that allow them to cause disease |
| Adhesion | ability to adhere to mucus membranes |
| Virulence Factors affecting ADHESION | capsule fimbriae/pili adhesins |
| Capsule | outer polysach layer- helps attachment- protects from phagocytosis |
| fimbriae/pili | necessary for some orgs to attach.. Neiserria and E. coli |
| Adhesins | surface proteins that bind host cells eg. S. pyogenes |
| Invasion | pathogens must be able to penetrate epithelium of skin they reach inner layer of skin cells through lesions or mucus membrane |
| Colonization | Once it has invaded the host, it can establish itself and grow |
| Virulence Factors affecting INVASION & GROWTH | O & Vi} salmonella Siderophores Leukosidin |
| O antigen - salmonella | O - (somatic antigen- part of LPS) cell surface polysaccharide- prevents phagocytosis |
| Vi antigen- salmonella | Vi - (capsular antigen) prevents complement binding & antibody mediated killing |
| Siderophores | compound that binds iron & make it available to the bacterial cell |
| Leukosidin | Staph aureus produces Leukosidin Leukosidin lyses white blood cells, decreasing host resistance |
| Localized infection | organisms grow locally at site of invasion |
| Systemic infection | organisms spread through body using blood or lymphatic systems |
| How do pathogens spread (disseminate) in the body? | they make virulence factors - many of these are enzyme which break down tissue |
| Examples of virulence factors that break down tissue | Hyaluronidase Collagenase Streptokinase Hemolysins |
| Hyaluronidase | destroys polysaccharides that glue animal cells together |
| Collagenase | breaks down collagen - produced by clostridium |
| Streptokinase | breaks down fibrin clots made by host to prevent spread - made by Strep pyogenes |
| Hemolysins | disrupt cytoplasmic membrane of animal cells - lyse red blood cells |
| 3 MAJOR GROUPS OF TOXINS | Exotoxins (worst) Enterotoxins Endotoxins |
| EXOTOXINS | protein secreted by bacteria that can damage tissues far away from infection site |
| Examples of EXOTOXINS | Diphtheria toxin Tetanus toxin Botulinum toxin |
| Diphtheria toxin | inhibits protein synthesis When Corynebacterium diphtheriae is lysogenized by phase β, tox genes are formed that makes the toxin |
| Tetanus toxin | Acts on motor neurons- causes continual contraction of muscles (lead to lock jaw) produced by Clostridium tetani- infects deep wounds |
| Botulinum toxin | prevents muscle contraction - results in respiratory /cardiac failure produced by Clostridium botulinum Botulism caused by ingesting toxin from canned foods |
| ENTEROTOXINS | proteins that act on small intestine (cause diarrhea) produced by food poisoning organisms eg. Clostridium, E coli, Salmonella |
| Example of ENTEROTOXIN | cholera toxin produced by vibriocholera |
| How does cholera toxin work? | Causes secretion of massive amounts of water in small intestine (diarrhea) - death by dehydration |
| ENDOTOXINS | when gram negative bacteria lyse lipid A portion of LPS is released |
| Organisms that release toxic Lipid A from LPS | E coli Salmonella Shigella causes diarrhea, fever, vomiting |
| Toxins that ****s up host function | AB toxins ADP Ribosylating toxins |
| AB toxins | B subunit binds to host cell delivers A subunit to cell 5 B subunits form pore for lipid A entry 'A' subunit is toxic- releases ADP Ribosyltransferase |
| ADP Ribosylating toxins | Cholera toxins Diphtheria toxins |
| Cholera toxins | ribosylates to overactivate adenylate cyclase cAMP activates ion transport, water follows} uncontrollable diarrhea |
| Diphtheria toxins | ribosylates elongation factor 2 <-- cell that makes proteins Diphtheria toxin blocks ribosome function - cell dies Diphtheria toxin forms pseudomembrane over trachea |
| How do pathogens survive once they enter host cell | cells ingest pathogens in phagosome - fuses with lysosome but some pathogens secrete proteins to prevent fusion (Salmonella, Chlamydia) some pathogens mature in acidic environment (Coxiella burnetti - Q fever) |
| How do pathogens survive once they enter host cell | some pathogens use hemolysin to break out and leave (Shigella dysenteriae, Listeria monocytogenes) |
| VIRUSES | influenza HIV |
| Influenza virus antigenic DRIFT | RNA polymerase does not correct replication errors - mutations in haemagglutinin gene |
| haemagglutinin gene | forms spikes on influenza virus- helps them attach to host |
| Mutation in haemagglutinin gene | allows virus to avoid immune system - virus spreads new vaccine needed each year |
| Influenza virus antigenic SHIFT | two strains infect host at the same time (chicken or swine) recombined virus have mix of chromosomes (alters several genes) cause of 1918/1919 influenza outbreak - largest loss of life in a single year |
| HIV | avoids host immunity by infecting immune cells binds multiple receptors for entry (CD4 & CCR-5-chemokine receptors) |
| Cells infected by HIV secrete | viral protein, which misregulates other immune system cells |
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