Detection of inducible clindamycin resistance in Staphylococcus aureus and coagulase-negative staphylococci - a study from South India

Background: Inducible clindamycin resistance is a major concern for the use of clindamycin to treat staphylococcal infections. Aims: To determine the prevalence of inducible clindamycin resistance in clinical isolates of Staphylococcus spp. and the susceptibility pattern of the isolates. Materials and Methods: A total of 300 isolates of Staphylococci spp. recovered from different clinical specimens were studied. All the Staphylococcus spp. were identified by conventional microbiological methods. Inducible clindamycin resistance was detected by double disk approximation test (Dtest).Results: Of the 300 isolates, 176 were identified as S. aureus, while 124 were coagulase negative staphylococci (CoNS). The rates of inducible clindamycin resistance in methicillin resistant S. aureus (MRSA), methicillin sensitive S. aureus (MSSA), methicillin resistant CoNS (MR-CoNS) and methicillin sensitive CoNS (MSCoNS) were 75.0%, 24%, 18.8% and 11.1%, respectively. The inducible clindamycin resistance was significantly more among MRSA compared to methicillin sensitive S. aureus (MSSA) (P value < 0.0001). Majority of the MRSA isolates were susceptible to clindamycin, vancomycin and linezolid, while most of them were resistant to erythromycin, gentamicin, ciprofloxacin, tetracycline and sulfamethoxazole-trimethoprim. Conclusion: In view of the significant in vitro inducible clindamycin resistance in Staphylococcus spp., we recommend that D test should be used as a mandatory method in microbiology laboratories to avoid misinterpretation of clindamycin result.