Pathogenic conversion is a process by which non-pathogenic strains acquire a virulence gene, such as a toxin, and become converted to pathogens.  In many cases a temperate bacteriophage has been found to have transferred the virulence gene.

Examples of toxin genes and virulence factors spread by bacteriophages include:

With respect to marine bacteriophage VpV262, the host species, Vibrio parahaemolyticus, infects shellfish and has exhibited pathogenic conversion to a form causing an epidemic of food-poisoning around the Pacific rim.

See Narita et al. 2001 and references therein for conversion in general.
See Chang et al. 2002 for conversion in Vibrio parahaemolyticus.