Prevalence of Methicillin-Resistant Staphylococcus aureus (MRSA) in Egyptian Water Buffaloes and Risk Factors for Subclinical Mastitis

Staphylococcus aureus (S. aureus) is one of the main causative agents of mastitis, which results in severe economic losses. In addition, methicillin-resistant S. aureus (MRSA) has been reported in dairy farms and in water buffaloes. The present study aimed to determine the prevalence of subclinical mastitis (SCM) in water buffaloes, associated risk factors for SCM, and prevalence of MRSA in positive milk samples for SCM. Milk samples (n = 385) from buffaloes were examined using the California mastitis test (CMT), and S. aureus was detected in positive milk samples using bacteriological and biochemical tests. In addition, MRSA was identified in positive S. aureus samples using PCR targeting the mecA gene. The results revealed that the prevalence of SCM among water buffaloes in the studied areas was 43.6%, and 61.9% (104/168) were identified as MRSA based on PCR targeting the mecA gene. In vitro antibiotic susceptibility testing found cefoxitin to be resistant and linezolid to be sensitive against MRSA isolates. In addition, the statistical analysis revealed that there was no significant association between the prevalence of SCM and locality or duration of lactation. The prevalence of SCM was strongly associated with age, parity, absence of teat dipping, hand cleaning of milker hands between milking, and in animals with a history of mastitis. Regular CMT can detect early SCM and improve udder sanitation and milking hygiene. In addition, continuous testing of antimicrobial drugs against MRSA isolates is necessary due to the importance of S. aureus in public health and the development of antibiotic resistance, such as methicillin.