MLST and Data Analysis

MLST genotyping of all isolates was performed as previously described (24). Each isolate was assigned an ST number, and novel sequence types were assigned and included in the MLST database at https://pubmlst.org/saureus/. The STs were grouped into clonal complexes (CCs) based on the designation published at https://pubmlst.org/organisms/staphylococcus-aureus/clonal-complexes. The associated STs shared by six of the seven loci were included into the same CCs (14). CC59, CC7, CC25, CC121, and CC398 were assigned according to previous publications (22, 28, 29). CC944 was assigned in this study because its associated ST, ST944, was the first reported type to the best of our knowledge. All isolates, including 72 MRSA, 4 OS-MRSA, and 668 MSSA isolates, were clustered based on the MLST data using the minimum spanning tree method in BioNumerics software (Applied Maths, Sint-Martens-Latem, Belgium). The unweighted pair group method with arithmetic mean was applied to design a dendrogram and antibiogram of the 72 MRSA and 4 OS-MRSA isolates using BioNumerics software. All the work regarding the handling of S. aureus was performed in a biosafety level 2 laboratory at Guangzhou Women and Children's Medical Center, and the person who performed the experiments had specific training and the biosafety level 2 standard microbiological regulations were strictly followed.