Epidemiology and antibiotic resistance of Staphylococcus aureus strains in south central China

Abstract

Objective To investigate the genotype distribution and antibiotic resistance of Stapylococcus aureus strains isolated from June 2011 to May 2012 in south central China.Methods The minimum inhibitory concentrations (MIC) of antibiotics were determined by agar dilution method.SCCmec (staphylococcal cassette chromosome mec) and agr (accessory gene regulator) typing on MRSA strains were performed using multiplex PCR.The hVISA (heterogeneous vancomycin-intermediate Stapylococcus aureus)strains were screened with MHA5T-screening agar (Mueller-Hinton agar containing 5 μg/ml teicoplanin)and the positive strains were further confirmed by PAP-AUC method (population analysis profile-area under conclusive evidence of the curve).Results A total of 352 consecutive and non-repetitive Stapylococcus aureus strains were isolated mainly from blood samples (40.1％) and secretion samples (24.7％),of which 118 strains were methicillin-resistant Stapylococcus aureus (MRSA) with a prevalence rate of 33.5％.The rates of antibiotic resistance of MRSA strains to cephalosporins,aminoglycosides,β-lactams,fluoroquinolones,rifampin,clindamycin,erythromycin and tetracycline were significantly higher than those of MSSA strains (P＜0.05),but the rates of antibiotic resistance of MRSA to chloramphenicol and trimethoprim/sulfamethoxazole were relatively low,which were 10.2％ and 7.4％,respectively.Strains resistant to vancomycin,teicoplanin,linezolid,daptomycin or tigecycline were not found.Twenty hVISA strains were detected from MRSA strains with a prevalence rate of 16.9％.The results of SCCmec typing showed that the dominant genotype of MRSA strains was SCCmec type Ⅲ,accounting for 80.5％,followed by type Ⅳ,accounting for 8.5％.There were two main types identified by agr typing,of which 81.4％ were of agr-1 type and 15.3％ were of agr-2 type.Conclusion SCCmec type Ⅲ and agr-1 type were the dominant genotypes of MRSA strains,and hVISA strains had a high prevalence rate of 16.9％.The phenomena of antibiotic resistance of Staphylococcus aureus strains was serious in south central China.Therefore,a rational use of antibacterial drugs (especially glycopeptide drugs) in clinic should be paid more attention in order to avoid the development of VISA and VRSA (vancomycin-resistant Stapylococcus aureus) strains. Key words: Stapylococcus aureus ; Methicillin-resistant Stapylococcus aureus ; hVISA ; SCCmec