| Introdution Macrolide,lincosamide and streptogramin B(MLSB) antibiotics are chemically distinct,but have similar effects on bacterial protein synthesis.Treatment of staphylococcal infections using MLSB antibiotics is commonplace but it is often accompanied by increased numbers of resistant strains.The mechanisms responsible for resistance to erythromycin in staphylococci are target site modification and active drug efflux.Target site modification is mediated by the presence of erm genes [erm(A),erm(B) and erm(C)]conferring resistance to MLSB antibiotics.Phenotypic expression of MLSB resistance can be inducible or constitutive.On the other hand, macrolide efflux is effected by membrane proteins encoded by the msr(A) genes and is specific for the 14- and 15-membered macrolides and streptogramin B(MS phenotype);lincosamide and streptogramin A antibiotics remain unaffected.The purpose of this study was to investigate the prevalence of Macrolide, lincosamide resistance in staphylococcal clinical isolates in Anhui hospitals,to examine the genetic mechanisms of resistance and to analyse molecular epidemiology by molecular methods.Objective To survey the bacterial resistance to macrolides and clindamycin in staphylococci isolated from Anhui hospitals.Methods MICs of 4 kinds of macrolides against 328 clinical isolates of Staphylococci were determined by agar dilution method.The inducible resistance of erythromycin to clindamcin was checked by D-test.The resistance gene of ermA,ermB,ermC and msrA in 158 S.aureus and 141 S.epidermidis with resistence to erythromycin were detected by PCR,while the genotypes of isolates were determined by ERIC- PCR.Results The resistance rates of MRSA to erythromycin,roxithromycin,azithromycin, clindamycin were 90.7%,96.9%,97.9%,84.5%,respectively.The resistance rates of MSSA to erythromycin,roxithromycin,azithromycin and clindamycin were 79.5%, 75%,76.1%and 72.7%.The resistance rates of MRSE strains to erythromycin, roxithromycin and azithromycin were 100%,and that to clindamycin was 99.1%.The resistance rate of MSSE to erythromycin was 94.1%,and that to roxithromycin, azithromycin were 97.1%.The majority of S.aureus and S.epidermidis isolates expressed the constitutive phenotype.Among 21 strains of staphylococci with erythromycin resistant and clindamycin sensitive,D-test positive strains were 9(9/21), which phenotypes were iMLS,and D-test negative were 12,whose phenotypes were MS.The prevalence of ermA,ermB,ermC and msrA was 3.2%,6.9%,39.9%,6.9% in S.aureus,and that was 2.1%,2.1%,55.3%,14.2%in S.epidermidis,repectively.A few isolates carried two genes.52 isolates were divided into 43 kinds of genotype with ERIC- PCR.Conclusion The resistant rates of staphylococci to macrolides were so high that macrolides should not be used for the treatment of infections caused by these isolates.The most prevalent resistance gene was ermC in staphylococci isolates with resistance to erythromycin.The clone dissemilation between strains may exist in resistance to macrolides of staphylococci. |
