Inducible Clindamycin Resistance in Methicillin Resistant Staphylococcus aureus Blood Culture Isolates in a Tertiary Care Hospital, Ranchi

Background: The resistance to antimicrobial agents among Staphylococci is an increasing problem. The management of the infections by it especially methicillin resistant ones is often difficult because methicillin resistant S. aureus is usually resistant to multiple antibiotics. This has led to renewed interest in the usage of Macrolide-Lincosamide-Streptogramin B (MLSB) antibiotics to treat Staphylococcus aureus (S. aureus) infections as an alternative to vancomycin. In vitro routine tests for clindamycin susceptibility may fail to detect inducible clindamycin resistance due to erm genes resulting in treatment failure, thus necessitating the need to detect such resistance by a simple D test on a routine basis. Materials and Methods: This retrospective study was conducted over the period of one year from 1st June 2019–1st June2020 in Microbiology laboratory of Rajendra Institute of Medical Sciences (RIMS), Ranchi to find the incidence of different phenotypes of MLSB resistance among S. aureus from blood culture isolates and their association with methicillin resistance. One hundred thirty five isolates of S. aureus were included in the study. Methicillin resistance was detected by cefoxitin disc diffusion method and inducible clindamycin resistance by erythromycin and clindamycin disc approximation test (D-test). Results: The overall blood culture done in 12 months were 1261, in which Staphylococcus aureus was isolated from 135 samples. Of the 135 isolates of S. aureus, 60 % (81/135) were MRSA. Erythromycin and clindamycin resistance was seen in 62.96 % (85/135) and 40 % (54/135) isolates respectively. Resistance to erythromycin and clindamycin were higher in MRSA as compared to MSSA (erythromycin-resistance: 74.07 % Vs 46.29 % and clindamycin resistance: 51.85 % Vs 22.22 %). The overall prevalence of iMLSB and cMLSB phenotype was 8.8 % (12/135) and 37.03 % (50/135) respectively. Both iMLSB and cMLSB phenotypes predominated in MRSA strains.