The two subspecies of Photobacterium damselae express virulence factors that are encoded by mobile DNA elements

Introduction Photobacterium damselae is a marine gram-negative bacterium of the family Vibrionaceae, widespread in marine environments, that includes strains classified into two distinct subspecies, namely subsp. piscicida and subsp. damselae. P. damselae subsp. piscicida is the causative agent of pasteurellosis, a disease affecting a number of fish species in marine aquaculture systems worldwide, but not affecting homeotherms. P. damselae subsp. damselae affects a variety of marine animals but has also been reported as the causative agent of fatal cases in humans. It is considered as a primary pathogen causing wound infections and hemorrhagic septicemia in different species of wild fish, as well as in reared fish of economical importance in aquaculture. Several important virulence factors have been reported in both subspecies (Osorio and Lemos, in press). In this report we show that some of these virulence factors like toxins, hemolysins or siderophore biosynthesis are encoded by mobile DNA elements and that some of them can be horizontally transmitted.