Distribution of sasX , pvl , and qacA/B genes in epidemic methicillin-resistant Staphylococcus aureus strains isolated from East China.

Background: Methicillin-resistant Staphylococcus aureus (MRSA) is a major nosocomial pathogen. Various virulence and antiseptic-resistant factors increase the pathogenicity of MRSA strains and allow for increased infection rates.

Purpose: The purpose of this study was to investigate the prevalence and distribution of virulence-associated and antiseptic-resistant genes from epidemic MRSA strains isolated from East China.

Methods: A newly designed multiplex PCR assay was used to assess whether the virulence-associated genes sasX and pvl and the chlorhexidine tolerance gene qacA/B were present in 189 clinical isolates of MRSA. Multilocus sequence typing (MLST) and Staphylococcal protein A ( spa ) typing of these isolates were also performed. The frequency of these genes in isolates with epidemic sequence types (STs) was investigated.

Results: Twenty STs and 36 spa types with five epidemic clones (ST5-t311, ST59-t437, ST5-t002, ST239-t030, and ST239-t037) were identified. The prevalence of sasX , pvl , and qacA/B in all isolates was 5.8%, 10.1%, and 20.1%, respectively. The prevalences of these genes in isolates with ST5, ST59, ST239, and other ST genetic backgrounds were all significantly different ( P <0.001). Isolates that had the highest frequency of sasX , pvl , or qacA/B were ST239 (33.3%), ST59 (28.9%), and ST5 (34.1%), respectively. The gene distribution pattern from all of the isolates showed that sasX - pvl - qacA/B+ , sasX - pvl + qacA/B -, and sasX+pvl - qacA/B - were closely associated with epidemic clones ST5-t311, ST59-t437, and ST239-t037, respectively.

Conclusion: There are significant differences in the prevalence of virulence-associated and antiseptic-resistant genes in epidemic MRSA strains. Using this information, more effective control and prevention strategies for nosocomial MRSA infections can be developed.