Analysis of clindamycin-induced resistance by erythromycin among 146 strains of Staphylococcus aureus

Objective To investigate the resistance of Staphylococcus aureus(SA) to erythromycin and clindamycin,and to detect the incidence of clindamycin-induced resistance by erythromycin and the induction of resistance genes.Methods The disk diffusion method recommended by the standards of Clinical and Laboratory Standards Institute(CLSI) was used,and cefoxitin disk diffusion test was used for the detection of meticillin-resistant Staphylococcus aureus(MRSA).The inducible resistance phenotype of erythromycin to clindamycin was analyzed by clindamycin and erythromycin double-disk diffusion method(D test),and the resistant gene was detected by polymerase chain reaction(PCR).Results In 146 strains of SA,MRSA accounted for 57.5%.SA resistant to both erythromycin and clindamycin were 82 strains,accounted for 56.2%.The erythromycin resistant and clindamycin susceptible or intermediate strains were 34 strains,which D test positive were 26 strains,the percentage for inducible resistance of erythromycin to clindamycin was 76.5%.The positive rates of D test were 80.0% and 71.4% in erythromycin resistant and clindamycin susceptible or intermediate MRSA and methicillin-sensitive Staphylococcus aureus(MSSA).The predominant gene for clindamycin resistance was erm.The predominant gene for constitutive resistance to clindamycin was ermA.The predominant gene for inducible resistance to clindamycin was ermC.Conclusions The detection of inducible clindamycin resistance in SA should be paid attention in clinical microbiology laboratories in order to guide physicians to select antimicrobial agents correctly such as macrolides and lincosamides.