Prevalence and antibiotic susceptibility profile of Staphylococcus aureus in clinical and subclinical mastitis milk samples

Background: Staphylococcus aureus is the most commonly isolated bacterial pathogen in clinical and subclinical mastitis among cows. This study aimed to investigate the prevalence of Staphylococcus aureus, including MRSA (Methicillin-resistant Staphylococcus aureus), in cows with clinical and subclinical mastitis in Cumilla and Chattogram regions. Additionally, antimicrobial resistance patterns were identified. Methods: A total of 429 milk samples were collected from different teats of 125 cows with clinical and subclinical mastitis across 15 farms. Standard bacteriological methods were applied to isolate and identify Staphylococcus aureus. Confirmation of Staphylococcus aureus was achieved through PCR for the presence of the nuc gene. Antimicrobial susceptibility testing was conducted for 11 antimicrobials. Isolates showing resistance to cefoxitin and oxacillin underwent mecA gene screening to identify MRSA. Multivariable logistic regression models were used to identify risk factors associated with the presence of Staphylococcus aureus Results: The study revealed that 13.54% (95% CI, 5.00–38.78%) of mastitis-infected cows tested positive for Staphylococcus aureus. Staphylococcus aureus isolates showed the highest resistance to penicillin, cloxacillin, and streptomycin (61.54%, 53.85%, and 53.85%, respectively), while manifesting the least resistance to ciprofloxacin, ceftriaxone, and sulfamethoxazole + trimethoprim (92%, 77%, and 77%, respectively), and gentamycin (69.23%). The prevalence of MRSA was 2.08% (95% CI, 1.55–38.34%). Conclusion: This study represents the first report of MRSA in clinical and subclinical mastitis milk samples in Bangladesh. The findings emphasize the importance of ongoing monitoring of Staphylococcus aureus and MRSA in mastitis cases, considering their prevalence and patterns of antimicrobial resistance.