Prevalence, Antimicrobial Susceptibility, and Enterotoxin Gene Detection of Staphylococcus aureus Isolates in Ready-to-Eat Foods in Shaanxi, People's Republic of China

Various ready-to-eat (RTE) foods are becoming increasingly popular in the world and could be easily contaminated with various microorganisms including certain pathogens. A total of 342 RTE food samples, including 32 cooked meats, 123 vegetable salads, 26 boiled peanuts, 109 cold noodles, and 52 dried tofu samples, were collected in Shaanxi Province, People's Republic of China, during the period of July to October 2012 and screened for Staphylococcus aureus. All S. aureus isolates were characterized by antimicrobial susceptibility and PCR for detecting nine enterotoxin genes (sea to sej). Overall, 25.4% of samples were positive for S. aureus, including 10 (31.3%) cooked meats, 34 (27.6%) salad vegetables, 6 (23.1%) boiled peanuts, 20 (18.3%) cold noodles, and 17 (32.7%) dried tofu samples. Of the isolated S. aureus organisms, 98.4% were resistant to at least one antimicrobial agent and 58.6% to three or more antimicrobials. Resistance to erythromycin (78.1%) and tetracycline (40.6%) was most frequently detected, while all isolates were sensitive to vancomycin and amikacin. Moreover, 55.5% of isolates were positive for one or more enterotoxin genes. The genes sed (25.8%) and sea (19.5%) were commonly detected among the isolates; seg, sei, and sej were not found. Our findings indicate that RTE foods in Shaanxi were contaminated with S. aureus isolates that harbored multiple toxin genes and exhibited multiple-drug resistance. Appropriated hygienic measures should be taken by producers, retailers, and consumers to reduce the risk posed by S. aureus in RTE foods.