Inducible clindamycin resistance in clinical isolates of Staphylococcus aureus.

Background: Staphylococcus aureus is one of the most important agents causing nosocomial infections. Inducible clindamycin resistance is an important concern, because common laboratory tests could not detect it. Objectives: The aim of this study was to detect the inducible clindamycin resistance by D-test method. Materials and Methods: A total of 209 clinical S. aureus isolates were collected and identified by conventional phenotypic tests. Antibiotic susceptibility pattern was detected by disc diffusion method. D-test was done using clindamycin (2 μg) and erythromycin (15 μg) discs according to the protocols of Clinical and Laboratory Standards Institute (CLSI). To detect methicillin resistant Staphylococcus aureus (MRSA), oxacillin disc was used and the results were confirmed by detection of mecA gene. Results: Of all 209 clinical S. aureus isolates, 207 (99%) were resistant to amoxicillin. All isolates were susceptible to vancomycin and linezolid. The rate of clindamycin inducible resistance was 4% (n = 8). This phenotype was not observed in MRSA strains. There was no significant difference between methicillin resistant and susceptible strains. Resistance to clindamycin and erythromycin was higher in MRSA strains. D+ phenotype was detected in 1 (1%) of all isolates. Methicillin resistance was detected in 66 (32%) isolates by oxacillin disc and mecA gene was detected by PCR. Conclusions: In our study, inducible clindamycin resistance rate was 4%; so it is necessary to conduct D-test regularly by disc diffusion for this bacterium. Resistance to erythromycin, clindamycin, ciprofloxacin and gentamicin was significantly higher in MRSA isolates than methicillin susceptible Staphylococcus aureus (MSSA), although the methicillin resistance prevalence was low.