Characterization of the Multi-Drug Resistance Gene in Methicillin-Resistant (MRSA) Strains Isolated From Animals and Humans in China.

We investigated -positive and -negative MRSA strains isolated from animals and humans in different geographical areas of China, from 2011 to 2016. Twenty -positive strains (15.6%) were identified from 128 MRSA strains including 17 from food animals and three from humans. The resistance rates and prevalence of the tested antibiotic resistance genes (ARGs) in the -positive MRSA isolates were higher than that in the -negative MRSA isolates. All -positive MRSA isolates were co-carrying and , and had significantly higher incidence rate vs. the -negative isolates ( < 0.05). In addition, multilocus sequence typing (MLST) assays showed that ST9 and -type t899 were the most prevalent ST and types in the study strains. However, all of the 20 -positive and 10 randomly selected -negative MRSA isolates were clonally unrelated as determined by pulsed-field gel electrophoresis (PFGE) analyses. Importantly, the gene was successfully transferred to a recipient strain RN4220 from 13 of the 20 -positive MRSA isolates by electroporation. Among these 13 -positive MRSA isolates, two different genetic contexts surrounding were determined and each was associated with one type of -carrying plasmids. Of note, the predominant genetic context of was found to be a Tn variant and locate on large plasmids (∼50 kb) co-harboring in 11 of the 13 MRSA isolates. Furthermore, the gene was also identified on small plasmids (∼ 7.1 kb) that co-carried in two of the 13 MRSA isolates. Our results demonstrated a high occurrence of multi-drug resistance in -positive MRSA isolates, and the spread of might be attributed to horizontal dissemination of similar -carrying transposons and plasmids.