Prevalence, Molecular Characterization, and Antimicrobial Susceptibility of Methicillin-Resistant Staphylococcus aureus from Different Origins in Sichuan Province, China, 2007-2015

Methicillin-resistant Staphylococcus aureus (MRSA) is a major multidrug-resistant (MDR) opportunistic pathogen that is responsible for nosocomial infections worldwide. The emergence of MRSA in food-producing animals has heightened concerns regarding the presence of MRSA in foods having an animal origin. The objectives of this study were to determine the prevalence of MRSA in different sources, including retail food, food-producing animals, and food handlers in Sichuan province. During 2007-2015, S. aureus was isolated from samples having different origins. Susceptibilities of MRSA to a panel of 12 antimicrobial agents were determined according to Clinical and Laboratory Standards Institute (CSLI) procedures. Pulsed-field gel electrophoresis, spa typing, staphylococcal chromosomal cassette (SCC) mec typing, and multilocus sequence typing (MLST) were used to characterize the relationship between these isolates. A total of 756 S. aureus were isolated from 11,067 samples. Of these, 52 isolates were classified as MRSA based on the presence of mecA genes. An antimicrobial susceptibility assay indicated that CHL-CLI-ERY-FOX-OXA-PEN-TET (n = 10) and CHL-CIP-CLI-ERY-FOX-OXA-PEN-TET (n = 8) were the two predominant MDR profiles in the isolates. Using 60% genetic similarity as a cutoff, the 52 MRSA isolates were grouped into 6 clusters having 34 pulsotypes. MLST typing showed seven multilocus sequence types (STs) with ST59 and ST9 being the most common. Six SCCmec types were identified in all MRSA isolates. The MRSA isolates had relatively low prevalence in Sichuan province. Clonal expansion is not involved in the dissemination of MRSA from food origins. Considering the threat of MRSA to public health, further surveillance is required to monitor the prevalence of food-related MRSA.