Derivation of rough attenuated variants from smooth virulent Aeromonas hydrophila and their immunogenicity in fish

Aeromonas hydrophila is a Gram-negative bacteria associated with many disease conditions of aquatic animals. Two rough attenuated variants were derived from two smooth virulent types of this bacterium by continuous passage separately in laboratory over a period of 8 years in brain–heart infusion agar. These variants were checked to be rough lipopolysaccharides (LPS) types and attenuated since they neither produced any disease nor mortality in the injected fishes. The immunogenic potential of these variants remained unaltered as compared to parent smooth types and fish immunized with these variants resisted the infection and mortality upon cross challenge. Because of their intact immunogenic potential and loss of virulence, they may be used as candidates for fish immunization.