Genomic Characterization of Livestock-Associated Methicillin-Resistant Staphylococcus aureus ST7 Isolates from a Case of Human Bacteremia in China

The detection of novel livestock-associated methicillin-resistant Staphylococcus aureus (MRSA) is important in both clinics and livestock. In this study, we report a MRSA-infected patient who was associated with livestock as a butcher, from whom we collected two MRSA strains FJ0318 and FJ0322. To further understand the correlation between these MRSA isolates and livestock, whole-genome sequencing and comparative genomic analyses were performed for these two isolates. Phylogenetic analysis revealed that these two strains were homologous. Multilocus sequence typing showed that these two strains belong to ST7, which is a common lineage in retail meat and meat products in China. The genetic islands in FJ0318 and FJ0322 were different from those in other common clones, such as ST59, ST8, and ST5. A mosaic plasmid with a sequence identical to that of the plasmid pE2 from livestock was found in strain FJ0318. Additionally, a novel prophage island was identified on the chromosome. Furthermore, the sequence of the island was similar to that of phage SP6 identified in livestock. ST7 may originate from livestock and be transmitted to communities, causing invasive infections.