Memories of a virulent past.

Studies on bacterial virulence and host-pathogen interactions usually rely on type strains isolated from human or veterinary populations. For instance, the El Tor strain N16961 has been extensively used to characterize Vibrio cholerae virulence, while E2348/69 is a default choice for studies on enteropathogenic E. coli interactions with host cells. Subsequent to isolation, such strains are passaged under laboratory conditions in rich medium, and often genetically manipulated to induce specific mutations or other alterations. While the cumulative knowledge gained by focused studies on a limited number of bacterial isolates allows for rapid scientific progress, strain diversity resulting from prolonged propagation and manipulation in different laboratories may lead to a distorted perspective and, at times, confound attempts to replicate specific experiments. Exploring such aberrations is an inevitable and necessary, if not always welcome, part of scientific progress.