Inducible clindamycin resistance in Staphylococcus aureus: a study from a tertiary care hospital of north India

ABSTRACT

Clindamycin is a preferred therapeutic option in erythromycin resistant Staphylococcus aureus skin and soft tissue infections. However, a major concern regarding its use for staphylococcal infections is the possible presence of inducible resistance to clindamycin. The present study was aimed to determine the incidence of constitutive and inducible clindamycin resistance in S.aureus isolates in our hospital. Retrospective study. Pt. BDS University of health Sciences, Rohtak, Haryana, India. A total of 250 consecutive, non-duplicate S. aureus strains were isolated from various clinical specimens, both from inpatients and outpatients. Antibiotic susceptibility tests were performed using Kirby-Bauer disc diffusion method. Methicillin resistance was detected by oxacillin disc on Mueller-Hinton Agar [MHA] plate supplemented with 2% NaCl. D-test was performed on all erythromycin-resistant and clindamycin-sensitive isolates to detect inducible clindamycin resistance. Observed and counted were methicillin resistance in S.aureus, constitutive and inducible resistance of the isolates to clindamycin, origin of the MLSBi isolates that is "community" or "hospital" and resistance of MLSBi isolates to other drugs. Among 250 S.aureus strains, 112 [44.8%] were found to be Methicillin-resistant Staphylococcus aureus [MRSA] and 20% had MLSBi phenotype. MRSA isolates showed higher inducible as well as constitutive resistance [p <0.0001] to clindamycin as compared to methicillin-sensitive S.aureus [MSSA]. All S.aureus isolates having MLSBi phenotype were sensitive to vancomycin and linezolid. The study strongly recommends the routine testing of in vitro inducible clindamycin resistance in S.aureus isolates as it will help in guiding therapy