Abstract: To investigate the prevalence, molecular characteristics and antibiotic resistance of Staphylococcus aureus isolated from the key links in the goat milk powder processing chain, we collected samples from different production stages of a goat milk powder plant. The S. aureus isolates were identified by using selective culture as well as nuc gene amplification. Twenty-one virulence genes, 16 common antibiotics, staphylococcal protein A (SPA), multi-locus sequence typing (MLST) and pulsed field gel electrophoresis (PFGE) typing of the isolates were investigated. The results showed that among the 112 samples collected, 6 samples (5.4%) were contaminated by S. aureus, including processing equipment (2 samples), processing personnel (2 samples), tank milk (1 sample) and floor powder (1 sample). Each isolate carried at least one toxin gene, and the detection rate of the panton-valentine leukocidin (pvl) gene was the highest (100%, 6/6), followed by sea, sec, see, seh, sek and seq (50.0%, 3/6), seg, sej and ser (33.3%, 2/6) and sed, sei, sem and seo (16.7%, 1/6). All the isolates were resistant to at least four antibiotics, and the isolates were most commonly resistant to ampicillin, cefoperazone, trimethoprim/sulfamethoxazole and penicillin (100.0%, 6/6), followed by erythromycin and amoxicillin/clavulanic acid (83.3%, 5/6), tetracycline (50.0%, 3/6) and gentamycin (16.7%, 1/6). In addition, all the strains were sensitive to oxacillin, cefoxitin, vancomycin and linezolid. Four spa types and 3 ST types were detected in all the isolates, and ST1-t127 (50.0%, 3/6) was the most predominant clone, followed by ST5-t002, ST5-t548 and ST188-t189 (16.7%, 1/6). For PFGE typing, these strains could be divided into 3 large clusters (I, II and III) and 4 pulsotypes (A, B, C and D), among which the processing equipment and the floor powder shared the same PFGE typing. The results showed that there was S. aureus contaminations in the processing of goat milk powder. Moreover, the key links of contamination were tank milk, processing equipment, processing personnel and floor powder, and there were some cross-contaminations in different processing links. Although the contamination rate is relatively low, it is necessary to carry out a long-term investigation on microbial contamination in different processing links of goat milk plants. Investigation should be taken to confirm the key contamination links, which can provide us with useful information to effectively control the spread of S. aureus in goat milk powder products.

Key words: goat milk powder processing plant; Staphylococcus aureus; virulence genes; antimicrobial susceptibility; molecular typing