Molecular Characterization of Rifampicin-Resistant <i>Staphylococcus aureus</i> Isolates from Retail Foods in China

This study investigated the molecular characteristics of rifampin-resistant (RIF-R) <i>Staphylococcus aureus</i> isolates recovered from 4300 retail food samples covering most provincial capitals in China, from 2011 to 2016. Of the 1463 <i>S. aureus</i> enrolled, 149 isolates (142 MSSA and 7 MRSA) were identified as rifampicin-resistant, including 20 high-level (MICs ≥ 8 μg/mL) and 129 low-level (MICs between 2 and 4 μg/mL) rifampicin-resistant strains. Most of the RIF-R <i>S. aureus</i> isolates were resistant to more than three antibiotics. The mutations in the rifampicin resistance-determining region of the <i>rpoB</i> gene were studied in all RIF-R strains. All of the strains presented the mutational change 481 His/Asn and five isolates presented an additional mutation, including 477 Asp/Tyr, 527 Ile/Met, and 466 Leu/Ser, respectively. Thirteen STs and twenty-one <i>spa</i> types were represented, in which five MRSA showed non-type SCC<i>mec</i> and the remaining MRSA belonged to SCC<i>mec</i> type IV—where, ST1-t127 was the predominant type from all of the isolates, while ST398-t034 was the predominant type for the MRSA isolates. In this study, we found that the food-related RIF-R <i>S. aureus</i> may have a unique genetic background selection. However, the scenario regarding the presence of RIF-R <i>S. aureus,</i> especially MRSA, in retail food in China is not favorable and warrants public attention.