Detection of inducible and constitutive clindamycin resistance among Staphylococcus aureus isolates in a tertiary care hospital, Eastern India

Subasini Majhi; Muktikesh Dash; Dharitri Mohapatra; Ashoka Mohapatra; Nirupama Chayani

doi:10.4103/2231-0770.184066

Detection of inducible and constitutive clindamycin resistance among Staphylococcus aureus isolates in a tertiary care hospital, Eastern India

Avicenna J Med. 2016 Jul-Sep;6(3):75-80. doi: 10.4103/2231-0770.184066.

Authors

Subasini Majhi¹, Muktikesh Dash¹, Dharitri Mohapatra¹, Ashoka Mohapatra², Nirupama Chayani¹

Affiliations

¹ Department of Microbiology, Sriram Chandra Bhanj Medical College and Hospital, Cuttack, Utkal University, Bhubaneswar, Odisha, India.
² Department of Microbiology, All India Institute of Medical Sciences, Bhubaneswar, Odisha, India.

Abstract

Introduction: Clindamycin is an excellent drug for skin and soft tissue Staphylococcus aureus infections, but resistance mediated by inducible macrolide-lincosamide-streptogramin B (iMLSB) phenotype leads to in vivo therapeutic failure even though they may be in vitro susceptible in Kirby-Bauer disk diffusion method.

Objective: The study was aimed to detect the prevalence of iMLSB phenotype among S. aureus isolates by double disk approximation test (D-test) in a tertiary care hospital, Eastern India.

Materials and methods: A total of 209 consecutive S. aureus isolates were identified by conventional methods and subjected to antimicrobial susceptibility testing by Kirby-Bauer disk diffusion method. Erythromycin-resistant isolates were tested for D-test.

Results: From 1282 clinical specimens, 209 nonrepeated S. aureus isolates were obtained. Majority of isolates 129 (61.7%) were methicillin-resistant S. aureus (MRSA). There was statistically significant difference between outpatients 60.1% and inpatients 39.9% (P < 0.0001). From 209 S. aureus isolates, 46 (22%) were D-test positive (iMLSB phenotype), 41 (19.6%) were D-test negative (methicillin sensitive [MS] phenotype), and 37 (17.7%) were constitutively resistant (constitutive macrolide-lincosamide-streptogramin B phenotype). The incidence of inducible, constitutive, and MS phenotype was higher in MRSA isolates compared to MS S. aureus (MSSA). The constitutive clindamycin resistance difference between MSSA and MRSA isolates were found to be statistically significant (P = 0.0086).

Conclusion: The study revealed 22% of S. aureus isolates were inducible clindamycin resistant, which could be easily misidentified as clindamycin susceptible in Kirby-Bauer disk diffusion method. Therefore, clinical microbiology laboratory should routinely perform D-test in all clinically isolated S. aureus to guide clinicians for the appropriate use of clindamycin.

Keywords: Constitutive macrolide-lincosamide-streptogramin B phenotype; D-test; Staphylococcus aureus; inducible macrolide-lincosamide-streptogramin B phenotype; methicillin-resistant Staphylococcus aureus; methicillin-sensitive Staphylococcus aureus; sensitive methicillin phenotype.