UNLABELLED

Mastitis caused by methicillin-resistant (MRSA) is a common issue in dairy farming, with sequence types (STs) related to cows mainly including ST9 and ST97. ST59, the predominant community-acquired clone, is still less reported in dairy cows. This study investigated the antimicrobial resistance patterns and molecular characteristics of 77 isolates obtained from eight dairy farms in the mid-east of China during 2019-2020, focusing particularly on the bovine mastitis-related livestock-associated MRSA (LA-MRSA) clone ST59. Among the 77 isolates, 14 isolates were identified as MRSA. A total of 20 STs were identified, with ST59 being the most prevalent among MRSA isolates (35.7%). All MRSA isolates possessed various Staphylococcal cassette chromosome (SCC) types, including XII ( = 5), IV.a ( = 4), IV.c ( = 2), IV.g ( = 2), and V ( = 1). Three MRSA lineages were identified: MRSA-ST59-t437-SCC IV.a/IV.g ( = 5), MRSA-ST9-t899-SCC XII ( = 4), and MRSA-ST88-t3622-SCC IV.c ( = 2). Approximately 44.2% of isolates demonstrated multidrug resistance. MRSA isolates showed a higher prevalence of antimicrobial resistance compared to methicillin-sensitive (MSSA) isolates. Virulence factor assays revealed that all MRSA isolates carried at least hemolysin genes and enterotoxin genes. ST59-MRSA strains showed the closest genetic relationship with human-derived strains, indicating a potential public health risk due to transmission of between livestock and humans. This study highlights the significant prevalence of the bovine mastitis-related LA-MRSA clone ST59 in the mid-east of China. Therefore, reinforcing monitoring and implementing preventive measures are essential to combat LA-MRSA.

IMPORTANCE

Obtained the prevalence and molecular characteristics of in dairy farms in the mid-east of China from 2019 to 2020. Recently identified livestock-associated methicillin-resistant (LA-MRSA) clones in cattle, including ST59-MRSA, may have originated from human sources, suggesting a potential risk for interspecies transmission.