Study of Using the D Test Method for Detection for Inducible Clindamycin Resistance of Staphylococcus Isolates and Analysis of Resistance

Objective To investigate the resistant phenotypeof erythromycin and clindamycin against staphylococcus and the prevalence of inducible clindamycin resistant in erythromycin-resistant staphylococcusin the local district.Methods Kirby-Bauer method was performed to detect the resistance of erythromycin and clindamycin against staphylococcus,cefoxitin disk diffusion method and D-test suggested by NCCLS 2004guidelines were used to detect methicillin-resistant staphylococcus(MRS)and the inducible clindamycin resistant in erythromycin-resistant staphylococcus.Results Of all 204 staphylococcus strains 90(44.12%) were resistant to both erythromycin and clindamycin(cMLS) constitutive resistance to clindamycin,57(27.94%) were resistant to erythromycin but susceptible to clindamycin and showed positive D test results(iMLS);32(15.69%) were resistant to erythromycin but susceptible to clindamycin and showed negative D test results(MS).Among the phenotype of resistant to erythromycin but susceptible to clindamycin the rates of inducible clindamycin-resistant of MRSA,MSSA,MRCNS andMSCNS were 65.22%,58.33%,67.65% and 60% respectively;Among all isolateserythromycin-resistant,the rates of inducible clindamycin-resistant were 31.25%,36.84%,31.94% and 30%.Conclusion The percentageof inducible clindamycin-resistance was 53.8%(35 /65) in clindamycin-susceptible staphylococcus isolates.The results indicated that D-test should be performed in clindamycin-susceptible isolates which were failing in clinical therapy by using clindamycin for staphylococcal infection.The detection of inducibleclindamycin resistance must be stressed in clinical microbiology laboratory toprovide good support for rational antibiotic therapy.