Study of inducible resistance of erythromycin to clindamycin in Staphylococcus

Objective To investigate the resistance of Staphylococcus to erythromycin and clindamycin and detect the percentage and gene for inducible resistance. Methods Disk diffusion method was used to test the resistance phenotype of Staphylococcus aureus and coagulase-negative staphylococcus according to the standards of NCCLS. The inducible resistance of erythromycin to clindamycin was checked by D-test and the gene for erythromycin ribosome methylase was detected by polymerase chain reaction.Results Co-resistance to erythromycin and clindamycin accounted for 62.7% and 54.8% in MRSA and MRCNS respectively. D-test positive rate was 17.7% among all Staphylococcus tested. The rate of inducible resistance to clindamycin (D-test positive) was 67.6% and 45.3% in Staphylococcus aureus and coagulase-negative Staphylococcus which possessed erythromycin resistant and clindamycin sensitive by individual disk diffusion test. The predominant gene for inducible resistance was ermC with the percentage of 74.5%.Conclusion The inducible resistance of erythromycin to clindamycin in Staphylococcus should be checked by D-test in clinical microbiology laboratory in order to help physicians to select MLSB antimicrobial agents correctly.