the cell

Three primary challenges a pathogen must overcome to cause disease

1. Infection (entering host and adhering via adhesins)
2. Replication and Survival (obtaining nutrients and evading immune host responses)
3. Transmission (exiting and spreading to new hosts)

Koch's Postulates

1. Pathogen must be present in every case of the disease.
2. Pathogen must be isolated from host and grown in pure culture.
3. Disease must be reproduced when pure culture is inoculated into a healthy host.
4. Pathogen must be recoverable from the experimentally infected host.

Exotoxins

Soluble proteins secreted by bacteria that directly cause disease symptoms and damage host tissues.

Virulence Factors

Genes or molecules (e.g., adhesins, toxins, immune evasion mechanisms) expressed by pathogens that enhance their ability to cause disease and survive within a host.

Adhesin

A surface molecule on a bacterium that binds specifically to a receptor on a host cell to enable colonization.

Ciliostatic substances

Pathogen-produced molecules (e.g., from Pseudomonas aeruginosa or Haemophilus influenzae) that inhibit ciliary movement in the respiratory tract, preventing mucus clearance.

Host cell receptors target of Type 1 and P-fimbriae in Uropathogenic E. coli (UPEC)

Type 1 fimbriae bind to bladder cells; P-fimbriae attach to kidney receptors (Globoside).

Mechanism of pedestal formation by Enteropathogenic E. coli (EPEC)

Uses a Type III secretion system to inject Tir protein into host cell membranes. Intimin on the bacterial surface binds Tir, triggering actin cytoskeleton rearrangement to form a pedestal.

Enzyme produced by Helicobacter pylori to neutralize stomach acid and enable colonization

Urease.

Survival mechanism of Mycobacterium tuberculosis within alveolar macrophages

Inhibits the fusion of lysosomes with the phagosome, preventing destruction inside the acidified lysosomal compartment.