Molecular characterization and detection of enterotoxins, methicillin resistance genes and antimicrobial resistance of Staphylococcus aureus from fish and ground beef.

Abstract

A total of 120 samples including 40 freshwaterfish(Oncorhynchus mykiss), 40 seawater fish (Sparus aurata) and 40 ground beef samples were examined for the presence of Staphylococcus aureus. The isolates were identified using biochemical tests and a PCR for the species-specific fragment (Sa442) and thermonuclease gene (nucA). The presence of staphylococcal enterotoxin genes (sea, seb, sec, sed and see), toxin genes (eta, etb, tsst), methicillin resistance gene (mecA) and some phenotypic virulence factors was also tested. Genotypic characterization of the isolates was analyzed by PCR-RFLP of the coa gene. Overall, 36 (30%) meat samples were contaminated with S. aureus. Of the 36 isolates, 3 (8.3%) were found to be positive for enterotoxin genes. Only 1 isolate (5.9%) from ground beef had the sea gene. In addition, 1 (12.5%) of the freshwater fish and 1 (9.1%) of the seawater fish carried both the sea and sed genes. The presence of seb, sec, see, eta, etb and tsst was not detected among the isolates of S. aureus. The amplified coa gene revealed five different clusters. Seven and six distinct RFLP patterns were obtained with AluI and HaeIII digestion, respectively. All isolates were found to be positive for slime, hemolytic and DNase activity while 41.7% of them were beta-lactamase positive. The presence of methicillin resistance was neither detected by PCR nor the disk diffusion method. A total of 94.4% of the isolates were resistant to at least one antimicrobial while 44.4% of them were resistant to at least two or more antimicrobials.