Aims:  To carry out a preliminary assessment of the occurrence of resistance to antimicrobials in bacteria that has been isolated from a variety of aquaculture species and environments in Australia. Method and Results:  A total of 100 Gram‐negative (Vibrio spp. and Aeromonas spp. predominantly) and four Gram‐positive bacteria isolated from farmed fish, crustaceans and water from crab larval rearing tanks were obtained from diagnostic laboratories from different parts of Australia. All the isolates were tested for sensitivity to 19 antibiotics and Minimal Inhibitory Concentrations were determined by the agar dilution method. Plasmid DNA was isolated by the alkali lysis method. Resistance to ampicillin, amoxycillin, cephalexin and erythromycin was widespread; resistance to oxytetracycline, tetracycline, nalidixic acid and sulfonamides was common but resistance to chloramphenicol, florfenicol, ceftiofur, cephalothin, cefoperazone, oxolinic acid, gentamicin, kanamycin and trimethoprim was less common. All strains were susceptible to ciprofloxacin. Multiple resistance was also observed and 74·4% of resistant isolates had between one and ten plasmids with sizes ranging 2–51 kbp. Conclusions:  No antibiotics are registered for use in aquaculture in Australia but these results suggest that there has been significant off‐label use. Significance and impact of study:  Transfer of antibiotic resistant bacteria to humans via the food chain is a significant health concern. In comparison with studies on terrestrial food producing animals, there are fewer studies on antibiotic resistance in bacteria from aquaculture enterprises and this study provides further support to the view that there is the risk of transfer of resistant bacteria to humans from consumption of aquaculture products. From the Australian perspective, although there are no products registered for use in aquaculture, antimicrobial resistance is present in isolates from aquaculture and aquaculture environments.

No abstract

Aims:  To determine the genetic determinants responsible for tetracycline resistance in oxytetracycline resistant bacteria from aquaculture sources in Australia. Methods and Results:  Twenty of 104 (19%) isolates tested were resistant to oxytetracycline (MIC ≥ 16 μg ml−1). Using polymerase chain reaction (PCR) amplification, one or more tet genes were detected in 15/20 (75%) isolates tested, but none were found in 5/20 (25%). tetM (50%) was the most common determinant, followed by tetE (45%), tetA (35%) and tetD (15%). Five of 12 oxytetracycline resistant isolates studied were able to transfer their R‐plasmid to Escherichia coli recipients of chicken, pig and human origin. tetA, tetD and tetM were found to be transferred while tetE was not transferred. Southern hybridization and PCR were used to confirm transfer of determinants. Conclusions:  Bacterial isolates from aquaculture sources in Australia harbour a variety of tetracycline resistance genes, which can be transferred to other bacteria of different origin. Significance and Impact of the Study:  Bacteria from aquaculture sources in Australia contribute to the resistance gene pool reservoir. The in vitro transfer of tetracycline R‐plasmid from aquatic bacteria to E. coli isolates from various sources is an indication of the potential public health risk associated with these resistance determinants.

Because of raising of large-scale high density prawn aquaculture techniques, production of this prawn worldwide is facing a serious threat from fatal diseases caused by nodaviruses and bacteria, particularly from the Vibrio species. The development of antibiotic resistance by Vibrio represents a potential threat to human health by exchange of resistant genes to human pathogens through food chain. This study aimed to determine antibiotic resistance profile of Vibrio isolates from giant fresh water Prawns (Macrobrachium rosenbergii) raised in Iran and to detect some antibiotic resistance genes in the isolates. A total of fifty giant fresh water prawns were processed for isolation of Vibrio species during February 2015 to August 2015. Identification of Vibrio isolates was done following standard biochemical methods. Phenotypic resistance of the isolates as determined by agar dilution method while polymerase chain reaction (PCR) method was used to detect the presence of erm, tetS, strA and sul2 genes in the isolates. Out of 50 prawns, 31 (62%) isolates of Vibrio spp. were reported, of which 20 (40%) were identified as V. parahaemolyticus, 10 (20%) were V. vulnificus and 1 (2%) were V. cholera. Over 90% of the tested strains showed susceptibility to SXT, AZM and NIT. In addition, strA and tetS genes were detected in all isolated Vibrio species. StrA gene was identified in 6 V. parahaemolyticus strains and also ermB and sul2 genes were not present in the isolate of V. cholera. The occurrence of multidrug resistance strains in the environment could be an indication of excessive usage of antibiotics in agriculture and aquaculture fields. This study has shown that giant freshwater prawns raised in Iran habour multidrug resistant Vibrio species.

No abstract