Prevalence and characterization of Staphylococcus aureus isolated from goat milk powder processing plants

Abstract

Staphylococcus aureus is a major concern for the food processing industry because of its virulence factors. The aim of this study was to determine the prevalence of S. aureus strains in goat milk powder processing plants, and to characterize these strains by antimicrobial susceptibility testing, pulsed-field gel electrophoresis (PFGE) and PCR. PCR detected genes encoding staphylococcal enterotoxin (sea to set), staphylococcal enterotoxin-like (selj to selv), toxic-shock syndrome toxin-1 (tst), exfoliative toxin (eta and etb), Paton-Valentine Leukocidin (pvl), and methicillin resistance (mecA). A total of 910 samples including 62 raw goat milk samples from a milking station and 848 samples from seven different sampling sites in four goat milk powder plants were collected. Out of 910 samples, 95 (10.4%) samples, including 34 (54.8%) of 62 milking station samples and 61 (7.2%) of 848 milk powder processing plant samples, were positive for S. aureus. 63.2% of 95 isolates contained one or more virulence genes. The five most predominant virulence genes were pvl (29.5%), sec (23.2%), ser (16.8%), tst (14.7%), and seb (12.6%). 90.5% of strains were resistant to at least one antibiotic. Resistance was most frequently observed to trimethoprim/sulfamethoxazole (89.5%), erythromycin (30.5%), tetracycline (22.1%), ampicillin (16.8%), chloramphenicol (15.8%), and rifampicin (9.5%). A total of 44 PFGE patterns were generated among all the isolates. PFGE demonstrated that some isolates with the same PFGE patterns came from different goat milk powder processing stages. Our findings indicate that S. aureus has spread among different goat milk powder producing locations. In addition, cross-contamination of S. aureus exists in goat milk powder processing stages. The presence of S. aureus strains in goat milk powder processing stages poses a potential threat to public health.