The Usage Of CgMLST In Clonal Change In Methicillin-resistant Staphylococcus Aureus

Objective:Methicillin-resistant Staphylococcus aureus(MRSA)is one of the principal multidrug resistant bacterial pathogens in healthcare settings,causing surgical site infection(SSI)as well as other severe invasive diseases.During the past few decades,the rapid dissemination of community-associated MRSA(CA-MRSA),which can infect populations lacking the typical risk factors for exposure to the healthcare system,has resulted in increasing reports of outbreaks in communities worldwide.Previous studies showed these community clones could also spread into hospitals.This study was performed to elucidate the changing epidemiology of methicillin-resistant Staphylococcus aureus(MRSA)in a Chinese teaching hospital.Methods:MRSA isolates were collected from sterile samples from 1 January 2013 to 31 December 2015,and tested susceptibility to common antimicrobial agents by agar dilution and double-disk diffusion method.Polymerase chain reaction(PCR)amplification of pvl genes.Whole genome sequences of all the isolates were sequenced using the Illumina second-generation high-throughput sequencing platform.We assembled and annotated the genome sequences by using CLC Genomics Workbench and performed MLST,spa and cgMLST typing by Ridom bioinformatics software.Results:A total of 292 MRSA infections were identified during the study period.Of these,most belonged to sequence type(ST)5(51.4%;150 of 292)and ST59(23.3%;68 of 292).The proportion of ST5 MRSA decreased from 68.3%in 2013 to 32.1%in 2015,and the proportion of ST59 MRSA increased from 8.9%to 41.0%.Core-genome phylogenetic analysis revealed that ST59 MRSA isolates exhibited wider genotypic diversity than ST5 MRSA isolates in both healthcare-onset and community-onset groups.Minimum spanning trees showed that a cluster of ST5 MRSA was circulating at SRRSH,whereas the ST59 MRSA infections were mostly sporadic.ST59 MRSA caused 45.2%of the 93 skin and soft-tissue infection cases and displayed lower levofloxacin(11.8%).ST59 healthcare-onset MRSA displayed enhanced virulence in the skin infection model and hemolysis assays.Notably,these isolates had virulence levels similar to those of classic community-associated MRSA strains.Conclusion:ST59 MRSA strains with high virulence potential have been replacing ST5 MRSA in predominance and causing nosocomial infections.cgMLST is a powerful tool to monitor changes in the epidemiology of MRSA in hospitals.