Bacterial Pathogenesis

Bacterial Pathogenesis OUT COMESBy the end of the sessions, learners will be able to: Define infection, specify the stages of the infectious process

Explain microbial virulence

Differences between endo and exotxins.

Important DefinitionsInfection: A process by which the organism enters into a relationship with the host.

Disease: A process by which the organism enters into a relationship with the host with occurrence of pathological changes and appearance of clinical manifestations.N.B.: Not all infections will proceed to be diseases but all diseases are infections.

Stages of the Infectious ProcessSource of infection

Mode of transmission

Portal of entry

Portal of exit

MICROBIAL VIRULENCEPathogenicity: The ability of a bacterial species to produce disease.Virulence: is the degree of pathogenicity.

N.B.: 1- Virulence is genetically determined by genes carried on chromosomes, plasmids, phages and pathogenicity islands.2- Microbial attenuation is the reduction of virulence by several means for the purpose of vaccine preparation.

Virulence Factors of BacteriaStructures or products that enable the organism to cause disease.

Virulence Factors may be:Adherence factors.Invasion factors: Enzymes.Antiphagocytic factors.Toxin production:Exotoxins.Endotoxins.

1- Adherence FactorsEnable the bacteria to attach to the host surface.Examples:

* Fimberiae of N.gonorrhoeae, E.coli help the attachment to the urinary tract.

* Glycocalyx of Staph and Streptococci adhere the organism strongly to heart valves.

2- Invasion FactorsA- Enzymes: * Leukocidin which destroy PMNL & macrophages. * IgA protease which degrades IgA.

B- Antiphagocytic factors: * Capsule (e.g. Strept. Pneumoniae) * Cell wall proteins of Gm+ve cocci. * Coagulase enzyme of Staphylococci.

3- Toxin production: Bacterial toxins are either exotoxins or endotoxins

Comparison between Exotoxin and Endotoxin

Exotoxins Endotoxins Source Secreted by livingorganisms both Gram-positive(mainly) and Gram-negative Part of the cell wallof Gram-negative organisms.Liberated upon celldisintegration Examples C. diphtheriae E. coli endotoxin Coding genesChromosome, PAI,Plasmids orBacteriophagesChromosome

Antigenicity Highly antigenic Poorly antigenic Nature Protein LPS (lipid A)

Toxoid: detoxified toxin obtained by treatment of exotoxin with formalin to remove its toxicity and retain its antigenicity. It can be used for immunization.

Exotoxins Endotoxins Heat stability Unstable Stable Detoxification Can be converted into toxoid Can not be converted into toxoid Specificity Every toxin has specific action Non-specific in action (all give fever and shock)Toxicity High Low

Dr.Azza Abdulazim

Dr.Azza Abdulazim

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