In vitro and in vivo study of an antimicrobial activity displayed by the redmouth disease agent, Yersinia ruckeri.

A soluble antimicrobial product has been detected in Yersinia ruckeri cultures. The contract droplets technique and the double agar layer method allowed to assess its bacteriostatic effect and the high susceptibility of other bacterial fish pathogens like Vibrio and Aeromonas. But it did not inhibit other strains of Y ruckeri. No correlation was found between the antimicrobial activity and the virulence of the strains. As mixed infections with A salmonicida and Y ruckeri could be obtained experimentally, the factor does not seem to confer any competitive advantage in fish tissues colonization.