Study on mechanism of macrolide resistance in Streptococcus pneumoniae

OBJECTIVE To investigate the antimicrobial susceptibility of Streptococcus pneumoniae isolated in Taizhou Hospital and their mechanisms of resistance to erythromycin so as to guide the rational use of drug in clinic.METHODS Antimicrobial susceptibility of 31 strains of S.pneumoniae was determined by KB disk diffusion method and VITEK identification system.Phenotypes of macrolide-resistant S.pneumoniae were determined using double disk test with erythromycin.ermB,mefA genes were amplified by PCR and sent for sequencing.RESULTS The antimicrobial susceptibility results showed that of the 31 S.pneumoniae isolates,the resistance rates to erythromycin,sulfamethoxazole,and tetracycline were 100.0%,64.5%,32.2%,respectively.No strain was resistant to penicillin,vancomycin and teicoplanin.31 clinical isolates were of the constitutive resistance phenotype.All erythromycin-resistant isolates had ermB(+)/mefA(+) genes.CONCLUSION The resistance of S.pneumoniae to erythromycin is serious in Taizhou Hospital.Target modification by erm methylase and gene modification by mef efflux pump are the main mechanism of macrolide-resistance in S.pneumoniae isolates.