The frequency and antibiotic resistance patterns of Livestock-associated Methicillin-Resistant Staphylococcus aureus (LA-MRSA) isolated from bovine-mastitis in Iran, a retrospective study

BACKGROUND AND OBJECTIVESBovine mastitis is an influential zoonotic infection that impacts cows' health and decreases the production yield of milk and dairy products. Methicillin-resistant Staphylococcus aureus (MRSA) is one of the most important causes of bovine mastitis, which makes the treatment challenging, and its transmission to humans through the consumption of infected meat or milk is very concerning. This study aimed to determine the frequency and antibiotic resistance patterns of MRSA isolated from milk samples of bovine mastitis in three provinces of Iran.MATERIALS AND METHODSA total of ۲۴۲ isolates of S. aureus recovered from milk samples of bovine mastitis were collected from previous studies performed from ۲۰۱۰ to ۲۰۲۰ in Tehran, Mashhad, and Hamadan provinces of Iran. The identity of the isolates was confirmed using the standard phenotypic and biochemical tests. MRSA strains were detected using the cefoxitin (۳۰ μg) disk agar diffusion (DAD) test, according to the guidelines of Clinical and Laboratory Standards Institute (CLSI). Subsequently, PCR of the mecA gene was applied to confirm MRSA isolates. Resistance of isolates against doxycycline (۳۰ μg), trimethoprim-sulfamethoxazole (۲۵ μg), clindamycin (۲ μg), cefazolin (۳۰ μg), and linezolid (۳۰ μg) were assessed by DAD test.RESULTS AND DISCUSSIONThe identity of ۱۴۷ isolates was confirmed as S. aureus, among which ۳۴ isolates (۲۳.۱۲%) were resistant to methicillin (MRSA). The mecA gene was detected in ۹۴.۱۱% of isolates (N= ۳۲/ ۳۴). The frequency of MRSA in Hamadan, Tehran, and Mashhad was ۶۸%, ۳۲.۳۵%, and ۰%, respectively. Isolates showed high resistance against cefazolin (۸۵%) and clindamycin (۷۹%) and had low resistance to trimethoprim-sulfamethoxazole (۳۵ %) and doxycycline (۳%), respectively. All isolates were susceptible to linezolid.CONCLUSIONThis study demonstrates that the frequency of MRSA in bovine mastitis in Iran is not low and should not be underestimated. In addition, the results of antibiotic sensitivity tests indicate the need to check the antibiotic resistance of the isolates before selecting the appropriate treatment strategy. Considering the importance of transmitting this pathogen from livestock products to the human population and its high-level resistance against most first-line antibiotic treatment regimens, it is necessary to conduct periodic studies to determine the accurate prevalence of LA-MRSA and its antibiotic resistance patterns throughout Iran.

کلیدواژه ها:

Bovine mastitis ، Staphylococcus aureus ، LA-MRSA ، antibiotic resistance ، Iran