Prevalence and antibiotic resistance of Staphylococcus aureus isolated from raw milk and dairy products collected from Alexandria, Egypt

The aim of the present study was to determine the prevalence and antibiotic susceptibility of Staphylococcus
aureus (S. aureus) isolated from raw milk and some dairy products collected from shops, grocery stores, street vendors
at different markets in Alexandria, Egypt and identification of the genes responsible for resistance to some important
antibiotics using polymerase chain reaction (PCR) technique. The results of the raw milk and dairy products
examined, 22.5% of the samples were positive for S. aureus. It was isolated from 29% of raw milk samples, 12.5%
of Kariesh cheese samples, 55% of White cheese samples, 10% of Ras cheese samples, 5.7% of yoghurt samples and
24.3% of cream samples. Antimicrobial susceptibility test revealed that all the isolates were susceptible to ciprofloxacin,
co-trimoxazole, linezolid, rifampin and vancomycin. Resistance to penicillin G, tetracycline, cefoxitin, chloramphenicol,
erythromycin and gentamycin were detected in 91.4%, 65.4%, 42%, 13.6%, 12.3% and 9.9% of the isolates,
respectively. The mecA resistance gene was identified in 91.2% of cefoxitin resistant S. aureus isolates, aacA-D was
detected in 87.5% gentamycin resistant isolates and ermC gene was detected in 100% of S. aureus isolates showed
macrolides resistance whereas ermA could not detected in any of them. The overall prevalence of methicillin resistant
S. aureus )MRSA( in the tested raw milk and dairy product samples was 8.6%. The highest methicillin resistant S.
aureus prevalence was reported in white cheese samples of 22.5% followed by raw milk, Ras cheese, cream, yoghurt
and Kariesh cheese with prevalence of 11%, 7.5% 7.14% 2.9% and 2.5%, respectively