Study on the genetic polymorphism of mec Ⅰ in the clinical isolates of methicillin-resistantStaphylococcus aureus / 中华检验医学杂志

ABSTRACT

Objective To investigate the genetic polymorphism of mec Ⅰ in the clinical isolates of methicillin-resistant Staphylococcus anreus(MRSA).Methods 40 isolates(MRSA)carrying mecA gene were selected randomly from the clinical isolates of Staphylococcus anreus from Jan,2005 to Aug,2006 in our hospital.The mec Ⅰ gene was detected by PCR followed with sequencing.Staphylococcal cassette chromosome mec(SCCmec)in MRSA were detected by multiplex-PCR.Agar dilution method was used for determining the MICs of oxacillin against MRSA.Results 35 of 40(87.5%)MRSA carried mec Ⅰ gene.All isolates carrying mec Ⅰ gene have mecI 202C→T substitution,which resulted in Gln at 68 aminophenol position replaced by stop condon.32 isolates carried single point mutation.3 isolates carried double-point mutation,including additonal A at 3 positon,A→C at 41 position and C→T at 142 position beside C→T at 202 position,respectively.Among 35 isolates carrying mec Ⅰ gene,there were 27 isolates of SCCmec Ⅲ, 7 isolates of SCCmec Ⅲ A and 1 isolate of SCCmec Ⅱ.Among 5 isolates with deletion of mec Ⅰ gene,there were 3 isolates of SCCmecⅣ,1 isolate of SCCmec Ⅰ and 1 isolate of non-known SCCmec tpye.The MICs of oxacillin were 256-512 ?g/ml,≥512 ?g/ml and 8-256 ?g/ml in 31 isolates with single point mutation at 202 position in mec Ⅰ gene,3 isolates with double-point mutation in mecI gene and 5 isolates with deletion of mec Ⅰ gene,respectively.1 isolate with single point mutation in mec Ⅰ gene had contrary result(MIC