Prevalence, Detection of Marker and Virulence Genes of Methicillin-Resistant Staphylococcus aureus (MRSA) Isolated form Milk and Dairy Products and their Antimicrobial Susceptibility

The present work was undertaken to study the prevalence, genetic profile and antimicrobial susceptibility of methicillin-resistant Staphylococcus aureus (MRSA) in raw milk and dairy products in Mansoura City, Egypt. MRSA was detected in 53% (106/200) among all milk and dairy product samples with prevalence rates of 75% (30/40), 65% (26/40), 40% (16/40), 50% (20/40), and 35% (14/40) in raw milk, Damietta cheese, Kareish cheese, ice cream, and yoghurt samples, respectively. The mean S. aureus counts were 3.49, 3.71, 2.93, 3.40 and 3.23 log₁₀ cfu/g in the tested raw milk, Damietta cheese, Kareish cheese, ice cream and yoghurt, respectively, with an overall count of 3.41 log₁₀ cfu/g. Unexpectedly, all of the S. aureus isolates (n=414) detected were genetically verified as MRSA strains. PCR analyses verified the existence of nuc, coa, and mecA genes in all of the 414 isolates. All of the 414 MRSA isolates were also positive for hla gene. The antimicrobial susceptibility pattern for the 414 MRSA strains against 13 tested antimicrobials indicated that the least effective drugs were penicillin G, cloxacillin, tetracycline, and amoxicillin with bacterial resistance percentages of 87.9%, 75.9%, 65.2% and 55.6% respectively, while the most effective antimicrobials against MRSA isolates were vancomycin, sulphmethazole/ trimethoprim, ciprofloxacin, netilmicin, and gentamicin, which revealed bacterial sensitivity percentages of 76.3%, 75.45 70.1%, 69.1%, and 63.3%, respectively. Of the 414 MRSA strains tested, 348 (84.1%) were multidrug resistance. This study presents the first genetic characterization of MRSA isolated from milk and dairy products in Egypt.