The retrospective study of oxacillin susceptible, mecA positive Staphylococcus aureus in China / 中华检验医学杂志

ABSTRACT

Objective The purpose of the study is to understand the epidemiology,distribution and molecular characteristics of oxacillin susceptible mecA positive Staphylococcus aureus (S.aureus).Methods Totally 1588 S.aureus isolates collected from 12 hospitals in 10 cities of China between 2010 and 2012 were retrospectively characterized.The isolates were characterized by antimicrobial susceptibility test of 20antimicrobial drugs.Three different methods (cefoxitin disc diffusion,agar dilution for oxacillin and cefoxitin) to detect oxacillin susceptible and mecA positive S.aureus were also compared.All the strains were confirmed to be S.aureus by detecting S.aureus specific genes by PCR (including nuc,femB,and mecA gene),which was viewed as the golden standard of MRSA.The molecular typing methods included SCCmec and spa typing.The statistical analyses were carried out in statistical product and service solutions (SPSS),Version 18.0.The significance level P was set at 0.05.Results According to the MICs of cefoxitin and oxacillin,a total of 60 isolates were oxacillin susceptible methicilin resistance Staphylococcus aureus (MRSA).Based on the differences of the specimen collection date,it is found that oxacillin susceptible MRSA have increased from 2010 to 2012 (P =0.05,95％ CI 0.045-0.056,X2 =6.099).These isolates were distributed in 9 major cities,and the highest prevalence is 30.0％ (18/60) in Guangzhou,followed by Beijing (18.3％,11/60),Wuhan (15.0％,9/60),Hangzhou (13.3％,8/60).Most of the isolates were from skin soft tissue infection (35％,21/60),blood stream infection (30％,18/60) and respiratory infection specimens (18.3％,11/60).The resistance rate to cefoxitin,erythromycin,clindamycin and tetracycline was 100％ (60/60),86.7％ (52/60),66.7％ (40/60) and 50％ (30/60),respectively.The molecular characterization showed that 21 spa and 5 SCCmec types were detected.The most predominant clone was spa t437-SCCmec Ⅳ (25.0％,15/60),followed by spa t437-SCCmecV (13.3％,8/60).Conclusions The detection rate of oxacillin susceptible MRSA is significantly higher from 2010 to 2012.The major clone is t437-SCCmec Ⅳ.The use of cefoxitin should replace oxacillin in detecting this type of MRSA.Further study is needed to confirm whether beta lactam antimicrobial agents should be used in the treatment of oxacillin susceptible mecA positive S.aureus.