GYRA MUTATIONS IN QUINOLONE-RESISTANT ISOLATES OF THE FISH PATHOGEN AEROMONAS-SALMONICIDA

gyrA mutations in quinolone-resistant isolates of Aeromonas salmonicid a have been detected by using PCR to amplify the quinolone resistance- determining region of gyrA and subsequent cloning and sequencing of PC R products. Comparison of nucleotide and derived amino acid sequences of PCR products from quinolone-susceptible and -resistant bacteria rev ealed a serine 83-to-isoleucine substitution in the gyrase A protein o f resistant isolates. One of the resistant isolates differed from the other by a two- to fourfold higher MIC of the fluoroquinolone enroflox acin and carried an additional alanine 67-to-glycine substitution, whi ch may contribute to the higher level of resistance.