First description of nonmotile Vibrio vulnificus strains virulent for eels

Nonmotile Vibrio vulnificus strains were isolated as pure cultures from body ulcers and internal organs of wild diseased European eels caught in a Mediterranean freshwater coastal lagoon. All 54 V. vulnificus isolates were nonmotile, indole-, ornithine decarboxilase-, mannitol- and cellobiose-positive, developed the opaque variant in culture, belonged to the O-antigenic serovar A and were highly virulent for eels by both intraperitoneal injection and immersion challenges. The nonmotile phenotype found in our V. vulnificus isolates was stable: nonmotile cells were always recovered from experimentally infected eels; no variation in the immobility of the V. vulnificus cells was observed for repeated subculture by daily passages on solid media, at different temperatures or incubation times and with or without magnesium sulfate. Many of the fla genes of Vibrio were present in the genome of the nonmotile strains (flaCDE and flaFBA for flagellins and flaH for the distal capping protein), although we observed by transmission electron microscopy that these V. vulnificus strains always lacked the polar flagellum. This is the first report on the existence of nonmotile wild-type V. vulnificus strains.