Utility of D test versus microdilution method in detecting inducible clindamycin resistance in Staphylococcus aureus

Objective To investigate the antibiotic resistance and prevalence of inducible clindamycin resistance in clinical isolates of Staphylococcus aureus.D test was compared with microdilution method in detecting the inducible clindamycin resistance in S.aureus.MethodsBacteria identification and susceptibility testing were performed by VITEK-2 system and Kirby-Bauer disk method.The inducible clindamycin resistance was determined by D test with the combination of erythromycin(ERY) and clindamycin(CL)(ERY and CL at 4 and 0.5 mg/L respectively) and microdilution technique in a single well of broth microdilution panel.ResultsThe resistance rate of the S.aureus isolates was higher than 50% to 14 of the 23 antibiotics tested.The highest resistance(both 97.0%) was to penicillin and ampicillin,followed by erythromycin and tetracycline(71.7% and 68.7% resistant).All isolates were susceptible to teicoplanin,vancomycin and linezolid.The percentage of S.aureus isolates susceptible to nitrofurantoin,chloramphenicol and trimethoprim-sulfamethoxazole was 95.0%,93.9% and 88.9% respectively.The prevalence of methicillin-resistant S.aureus(MRSA) and methicillin-sensitive S.aureus(MSSA) in the 99 isolates was 63.6% and 36.4%,respectively.Ten(10.1%) of the 99 isolates showed resistant to erythromycin but susceptible to clindamycin.All the 10 isolates showed inducible resistance to clindamycin.The broth microdilution method performed identically with D test.ConclusionsResistance of S.aureus is quite serious.Both D test and microdilution methods can be used to detect the inducible clindamycin resistance in S.aureus.