Mechanisms of bacterial host-to-host transmission.

SUMMARYBacterial pathogens must navigate complex host environments to thrive, replicate, and ultimately transmit to new hosts. Effective transmission is critical for pathogen propagation and often requires overcoming host defenses and exploiting environmental conditions. The mechanisms used by bacterial pathogens to cause disease have been studied for decades, and numerous virulence factors have been identified and characterized through the use of genetic tools and animal models. While insightful, these discoveries have only scratched the surface of our understanding of disease mechanisms. Even less well understood is how pathogens move from an infected host to colonize and establish infection in a new host. Pathogens can move between hosts via direct and indirect modes, relying on numerous routes, such as respiratory, fecal-oral, direct contact, vector-borne, and vertical transmission. Recent advances in animal models for the study of bacterial transmission have enabled a more accurate recapitulation of transmission between humans. This review summarizes the current knowledge of bacterial transmission factors and animal models of transmission, and how these tools are advancing our understanding of the transmission mechanisms used by bacterial pathogens.