Molecular Epidemiology and Virulence Features of Staphylococcus aureus Bloodstream Isolates in a Regional Burn Center in China, 2012-2016

Staphylococcus aureus is known to be a predominant pathogen causing bloodstream infection (BSI) from burn units. Our study aimed to perform the clinical epidemiological analysis and virulence features of S. aureus strains isolated from the burn patients with BSI from a burn center in southeastern China during 2012-2016. A collection of 112 S. aureus isolates causing BSI from burn center of a tertiary care hospital in China was carried out. Antimicrobial susceptibility testing was conducted in accordance with the Clinical and Laboratory Standards Institute (CLSI) guidelines. Toxin gene profiles, multilocus sequence typing, staphylococcal protein A (spa) typing, accessory gene regulator (agr) locus typing, staphylococcal cassette chromosome mec (SCCmec) typing, and dendrographic analysis were used to characterize and analyze these isolates. Of 112 S. aureus isolates, 52 (46.4%) were methicillin-resistant S. aureus (MRSA) and 60 (53.6%) were methicillin-susceptible S. aureus (MSSA). ST239-SCCmec III-t030-agr I was the major prevalent clone (26 from MRSA and 6 from MSSA), which was followed by ST239-SCCmec III-t037-agr I (12, 10.0%) and ST5-SCCmec II-t002-agr I (11, 9.2%). The genotyping results showed high genetic diversity in molecular characterization and toxin gene profiles of the strains. Carriage of tsst-1 was mainly associated with ST239-SCCmec III-t030-agr I and ST30-SCCmec IV-t062-agr III, whereas lukS/F-PV was distributed in different clones. In conclusion, ST239-SCCmec III-t030-agr I is the commonest clone causing BSI among burn patients in eastern regions of China. In contrast to MRSA, polyclonality was statistically significantly higher among MSSA isolated from burn patients with BSI.