Inducible clindamycin resistance in Staphylococcus aureus: A study from North India

Background: The resistance to antimicrobial agents among Staphylococci is an increasing problem. The resistance to macrolide can be mediated by msr A gene coding for efflux mechanism or via erm gene encoding for enzymes that confer inducible or constitutive resistance to macrolide, lincosamide and Type B streptogramin. Aim: The present study was aimed to find out the percentage of Staphylococcus aureus having inducible clindamycin resistance (iMLS B) in our geographic area using D-test. Also, we tried to ascertain the relationship between Methicillin-resistant Staphylococcus aureus (MRSA) and inducible clindamycin resistance, association of these iMLS B isolates with community or nosocomial setting and treatment options for these iMLS B isolates. Settings and Design: A total of 200 non-duplicate Staphylococcus aureus isolates from various clinical samples from both outdoor and indoor patients were studied. Materials and Methods: Susceptibility to routine antimicrobial agents was carried out using Kirby Bauer method. Methicillin resistance was detected by oxacillin disc on Mueller Hinton agar (MHA) supplemented with 2% NaCl. D-test was performed on all erythromycin-resistant and clindamycin-sensitive Staphylococcus aureus strains to detect inducible clindamycin resistance. Results: Among 200 Staphylococcus aureus strains, 50 (25%) were found to be MRSA and 36 were D-test positive. Also, MRSA isolates showed both higher inducible resistance and constitutive resistance to clindamycin as compared to Methicillin-sensitive Staphylococcus aureus (MSSA). Out of 36 isolates of Staphylococcus aureus showing inducible clindamycin resistance, 24 were from the outpatient department and 12 were recovered from indoor patients. All isolates of Staphylococcus aureus showed 100% sensitivity to vancomycin and linezolid. Conclusions: Clindamycin is kept as a reserve drug and is usually advocated in severe MRSA infections depending upon the antimicrobial susceptibility results. We have reported a higher incidence of iMLS B from both community (66.67%) as well as hospital (33.33%) setup. Therefore clinical microbiology laboratory should report inducible clindamycin resistance routinely.