Table 1 Classification of bacterial virulence mechanisms

   • 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