Characterization of drug-resistant Staphylococcus aureus isolated from poultry processing plants in Western Australia

Poultry processing plants can provide a favourable environment for the survival and transmission of Staphylococcus aureus. It is known that infections due to antibiotic-resistant strains of S. aureus are an increasingly serious problem clinically and, since antibiotic exposure in food-animal species may lead to antibiotic-resistant bacteria, it is possible that processed poultry may constitute a reservoir for disseminating antibiotic-resistance into the community. The present study was undertaken to determine the prevalence of antimicrobial-resistant S. aureus in two poultry processing plants, and to characterize the isolates by antimicrobial susceptibility and chromosomal and plasmid DNA analysis. One hundred and twenty-six S. aureus were isolated from two poultry processing plants in Western Australia. All were sensitive to 14 of the 26 antimicrobials tested and all isolates were resistant to at least one antibiotic and one chemical marker, the prominent resistance combination being to penicillin and cadmium (89%). Forty-six (36.5%) of the isolates were resistant to six or more of the antimicrobial agents tested. Overall there were no consistent resistance patterns for the isolates and no consistent patterns were found between and within the two processing plants. There were 24 epidemiologically unrelated Sma1 contour-clamped homogeneous electric field (CHEF) groups and 17 different plasmid profiles detected among the isolates. All isolates were found to harbour from between one to seven plasmids. The majority of isolates carried at least one large plasmid (22-48 Kb), and one or more small plasmids (1-3 Kb). Some isolates with epidemiologically related CHEF patterns had similar plasmid profiles and resistance patterns.