Table 1.

Classification of bacterial virulence mechanisms

1. Adhesion

• Loose adhesion

• Intimate adhesion

2. Invasion

• Transcellular (uptake across cell membranes using host cell uptake mechanisms, such as phagocytosis and microfold cell sampling or pathogen-directed endocytosis)

• Intercellular (traversal of an epithelial barrier between epithelial cells)

3. Intracellular survival mechanisms

• Within cytoplasm following escape from phagosome or endocytic vesicle

• Within an endocytic vesicle via avoidance of phagolysosome formation or autophagocytic pathway

• Prevention of host cell apoptosis

4. Extracellular survival mechanisms

• Antiphagocytic mechanisms (such as triggering of phagocyte apoptosis, subversion of lysosome fusion with the phagosome, resistance to oxygen free radicals)

• Serum resistance via preventing complement activation on the bacterial cell surface and inhibition of membrane attack complex insertion into the bacterial membrane

5. Nutrient acquisition

• Iron acquisition systems

6. Damage host cells and tissues

• Cytotoxins

• Enzymes that degrade extracellular matrix components

7. Motility

• Swimming (for example, flagella)

• Twitching motility (for example, type IV pili)

8. Biofilm formation

9. Regulation of virulence

• Sense environment and regulate transcription/activation of virulence genes

• Sense other bacteria (quorum sensing) and regulate transcription/activation of virulence genes