Emergence of livestock-associated MRSA ST398 from bulk tank milk, China.

Objectives To detect livestock-associated MRSA (LA-MRSA) ST398 from bulk tank milk in China and to determine the phenotypic and genomic characteristics of the strains. Methods LA-MRSA ST398 strains were isolated from bulk tank milk samples in Shanghai and their susceptibilities to antimicrobials were determined using the broth dilution method. Genomic characterization of MRSA ST398 strains was performed by WGS and their evolutionary relationships were assessed by phylogenetic analysis. Results Two LA-MRSA ST398 isolates were recovered from bulk tank milk samples in two geographically distant farms in China. Whole-genome analysis strongly suggested that the LA-MRSA ST398 strains were closely related to the highly virulent hospital-associated MRSA (HA-MRSA) ST398 strains in China. Conclusions The presence of LA-MRSA ST398 in bulk tank milk might be a serious threat to public health, highlighting the need for active surveillance of LA-MRSA in healthy cattle in China.