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.

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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.

Our results suggest the resistant strains are persisting environmental isolates that have been acquired by the different livestock species. Furthermore, the different treatment practices in poultry and pigs have resulted in differences in resistance profiles in Campylobacter isolates.

Methicillin-resistant staphylococci (MRS) pose a challenge to clinicians and health administrators in human medicine, but MRS infections in cats and dogs are not perceived as a problem in veterinary medicine. Ten methicillin-resistant staphylococcal isolates obtained from healthy and diseased cats and dogs were subjected to partial DNA sequencing of the mecA gene. Sequence analysis shows that MRS isolates from both healthy and diseased cats and dogs can harbor the mecA gene. The mecA genes of animal isolates were identical to that found in human MRS strains, and therefore the possibility of zoonotic transfer must be considered.Methicillin-resistant Staphylococcus aureus (MRSA) isolates have been identified as a serious cause of nosocomial infections, and more recently, community-acquired MRSA has been recognized as an emerging problem in a number of countries. The resultant infections include a range of conditions from minor skin infections to severe life-threatening conditions. Staphylococcal resistance to methicillin is attributable to multiple mechanisms (6), but the most important mechanism from the standpoint of nosocomial infections and treatment appears to be intrinsic resistance and is due to the expression of low-affinity penicillin-binding protein 2A (11,22,30). Penicillin-binding protein 2A is highly conserved among staphylococci and is encoded by the chromosomal gene mecA (3).Cats and dogs have become an integral part of modern society, especially in developed countries, and attention is given to their care and welfare. A large proportion of the human population is in contact with cats and dogs on a daily basis, and so there is the potential for transfer of bacteria or resistance genes between companion animals and humans (5, 9). Studies conducted in recent years have shown that staphylococci isolated from cats and dogs have become resistant to methicillin (8,16,19,20,24,25,26,31,33). However, none of these studies on methicillin-resistant staphylococci have compared the mecA gene from these animals' isolates with that from human MRSA strains. Although methicillin or other antistaphylococcal penicillins such as oxacillin and cloxacillin are not commonly used antibiotics in the treatment of staphylococcal infections in cats and dogs, there are clear public health implications related to the presence of methicillin-resistant staphylococci on the skin of cats and dogs. In this study, we report the isolation, antibiotic susceptibility, and partial nucleotide sequence determination of 2 kbp of the mecA gene of staphylococci isolated from diseased and healthy cats and dogs. MATERIALS AND METHODS Isolation of staphylococci.A total of 55 healthy cats and 51 healthy dogs undergoing desexing or boarding at two veterinary clinics in Adelaide were sampled. One hundred forty-one diseased dogs and five diseased cats with various skin infections were also sampled. Staphylococci were isolated from swabs taken from the skin and lesions of the animals. A selective medium, GiolitiCantoni broth (Oxoid, Basingstoke, Engl...