Resistance determinants of pseudomonas species from aquaculture in Australia

Abstract

There is limited information on antibiotic resistance determinants present in bacteria of aquaculture origin in Australia. The presence of integron and other resistance determinants was investigated in 129 Pseudomonas isolates derived from nine freshwater trout farms in Victoria (Australia). Polymerase chain reaction (PCR) was carried out for the detection of integrase genes Int1, Int2 and Int3, gene cassette array, integron-associated aadA, beta-lactamase resistance genes blaTEM and blaSHV. Genes coding for efflux pump mexA, mexB and oprM were also investigated as well as cadA and czr which are known to mediate resistance to cadmium. Class 1 integrons were detected in 30/129 (23%) isolates while class 2 and class 3 was not detected in any of the isolates. aadA gene was detected in 28 of the 59 integrase positive isolates which are also resistant to streptomycin. The strA-strB, blaTEM or blaSHV genes were not detected in any of the strains. mexB was detected in 85/129 isolates and cadA gene in 59/92 isolates tested. The sequence analysis mexB from this study demonstrated similarity to the RND multidrug efflux transporter mexB and its homologue TtgB which in addition to multidrug efflux also transports toluene out of the cell. The sequence analysis of cadA confrms similarities to the cadmium translocating P-type ATPases, cadA of various Pseudomonas spp. Pseudomonas spp. carrying integrons, efflux gene and cadmium resistance genes are present in farm-raised fish and sediments even though no antibiotics were licensed for use in Australian aquaculture at the time of the study. © 2012 Ndi OL, et al.