Antimicrobial Resistance Properties And Enterotoxigenic Gene Profile Of Methicillin-Resistant And Methicillin-Susceptible Staphylococcus Aureus Isolates From Raw Milk

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Elnaz Kabiri , Zohreh Mashak


Both methicillin-resistant and methicillin-susceptible Staphylococcus aureus bacteria are emerging causes of food-borne diseases. Raw milk of animal species may consider a reservoir of MRSA and MSSA strains. The present survey was done to assess the prevalence and antibiotic resistance properties of MRSA and MSSA strains isolated from raw milk samples of animal species. Three hundred and eighty raw milk samples were collected from cow, sheep, and goat species. S. aureus was identified using culture and biochemical tests. MRSA and MSS identification were done according to cefoxitin and oxacillin antibiotic resistance and mecA gene presence. The pattern of antibiotic resistance was determined by disk diffusion. The distribution of antibiotic resistance genes was determined using PCR. Forty-two out of 380 (11.05%) raw milk samples were contaminated with S. aureus. MRSA and MSSA strains were identified in 64.28% and 35.72% of S. aureus isolates. MRSA isolates harbored the uppermost resistance rate toward tetracycline (100%), penicillin (100%), trimethoprim-sulfamethoxazole (66.66%), erythromycin (66.66%), and ciprofloxacin (66.66%). MSSA isolates harbored the uppermost resistance rate toward tetracycline (46.66%), erythromycin (46.66%), penicillin (40%), azithromycin (40%), and gentamicin (40%). BlaZ (100%), aacA-D (62.96%), tetK (51.85%). cat1 (48.14%), and dfrA1 (44.44%) were the most commonly detected antibiotic resistance genes amongst the MRSA, while aacA-D (26.66%), ermA (26.66%), msrA (26.66%), tetK (26.66%), and gyrA (26.66%) were the most commonly detected amongst the MSSA strains. Raw milk samples may be sources of resistant MRSA and MSSA, which pose a hygienic threat in their consumption. MRSA harbored a higher prevalence of resistance and also the distribution of antibiotic resistance genes.  

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