Abstract: To investigate the key links of Staphylococcus aureus pollution in the broiler slaughtering process and the molecular characteristics and antimicrobial susceptibility of S. aureus isolates, we collected microbial samples from different production stages (anal swabs from live chicken, soaking, pre-cooling, segmentation, and storage) in a broiler slaughterhouse in Shaanxi Province four times. S. aureus isolates were isolated and identified by selective culture and polymerase chain reaction (PCR) amplification of the nuc gene. Twenty-three virulence genes, 27 drug resistance genes, resistance to 16 common antibiotics, staphylococcal protein A (SPA), multi-locus sequence typing (MLST), and enterobacterial repetitive intergenic consensus-polymerase chain reaction (ERIC-PCR) typing of the isolates were investigated. The results showed that 32 of the 144 samples collected (22.2%) were contaminated by S. aureus. The S. aureus contamination rate in the defeathering process was the highest (40.0%, 12/30), followed by the segmentation (26.7%, 8/30), pre-cooling (21.9%, 7/32), and storage processes (15.6%, 5/32). S. aureus was not detected in the anal swabs. Sixteen virulence genes were detected. Among them, the pvl, seb, sek, seg, sei, sem, sen, seo, seu, sep, and seq genes were detected frequently. Additionally, 96.9% (31/32) of the isolates carried novel enterotoxin genes. Only four drug resistant genes were detected, including blaZ, tet(K), erm(B), and aac(6′)/aph(2′′). The isolates showed resistance to seven of the 16 antibiotics tested, and were most commonly resistant to trimethoprim/sulfamethoxazole, followed by ampicillin, penicillin, tetracycline, ciprofloxacin, erythromycin, and gentamicin. Five clonal types (ST7-t091, ST5-t010/t002 and ST59-t437/t441) and 4 ERIC-PCR clusters (I1-I4) were detected in all the isolates. The isolates from different stages of the broiler slaughtering process had the same ERIC-PCR map, molecular type, drug-resistance profile, virulence gene profile, and antibiotic resistance gene profile. The results showed that S. aureus contamination was common in broiler slaughtering process. Cross-contamination could be observed among different processing stages, among which scalding was considered to be the key link of contamination. It was also found that the virulence genes carried by the isolates had a significant correlation with the molecular type (P < 0.05). The monitoring of different slaughter steps is helpful to identify the critical control points of S. aureus pollution, which can effectively prevent and control the outbreak of food-borne diseases.

Key words: Staphylococcus aureus; broiler slaughter; molecular characteristics; antimicrobial susceptibility