Abstract
Objectives: Staphylococcus aureus is often linked with human infection. Clindamycin is one of the key substitute antimicrobial agents in the treatment of S. aureus, especially in methicillin-resistant S. aureus (MRSA) infections. Inducible macrolide-lincosamide-streptogramin B (iMLS B) resistance is a crucial factor in antimicrobial susceptibility testing. The intention of the research was to identify S. aureus from distinct clinical specimens and investigate the prevalence of inducible clindamycin resistance among them and also study their association with MRSA.
 Methods: A descriptive cross-sectional study was accomplished in the Dept. of Microbiology CMC-TH, Nepal from January 2018 to December 2020 with 525 non-repeated S. aureus obtained from a different clinical specimen. Antibiotic susceptibility test was performed by Kirby–Bauer disc diffusion method. MRSA was detected using cefoxitin (30 μg) and results were interpreted as stated by CLSI. “D-Test” was done by applying erythromycin (15 μg) and clindamycin (2 μg) as per CLSI guidelines. Data were analyzed using SPSS IBM version 20.
 Results: Among 525 isolates, there were 315 (60.00%) MRSA. Results of D test analysis showed that 280 (53.33%) were MLSB sensitive while 245 (46.67%) were MLSB resistant; where 80 (15.24%) iMLSB with D zone, 100 (19.05%) constitutive MLSB (cMLSB) phenotype, and 65 (12.38%) MS phenotype. Of a total of 80 iMLSB, a significant proportion of 64 (80.00%) was MRSA (p<0.001). All the isolates were sensitive to vancomycin, teicoplanin, and linezolid. The prevalence of both iMLSB and cMLSB was high among MRSA.
 Conclusion: In this study, cMLSB phenotype was predominant (19.05%) followed by iMLSB phenotype (15.25%) and then MS phenotype (12.38%). Inducible iMLS B phenotypes, as well as cMLSB, are higher among MRSA. It is advisable to include “D-Test” as a part of regular antibiotic susceptibility testing to detect iMLSB resistance among S. aureus.
Highlights
Staphylococci were first identified by Sir Alexander Ogston in 1880, in pus from a surgical abscess in a knee joint; later in 1884, Freidrich Jukius Rosenbach distinguishes Staphylococcus aureus from Staphylococcus epidermidis [1]
All the isolates were sensitive to vancomycin, teicoplanin, and linezolid. The prevalence of both Inducible MLSB (iMLSB) and constitutive MLSB (cMLSB) was high among methicillin-resistant S. aureus (MRSA)
The present study demonstrated a higher prevalence of both iMLSB and cMLSB among MRSA as compared to MSSA
Summary
Staphylococci were first identified by Sir Alexander Ogston in 1880, in pus from a surgical abscess in a knee joint; later in 1884, Freidrich Jukius Rosenbach distinguishes Staphylococcus aureus from Staphylococcus epidermidis [1]. S. aureus is small, ovoid, Grampositive cocci found typically in grape-like clusters or may occur in pairs or singly [2] It commonly colonizes the skin and noses of healthful individuals. Harmless at these sites, it may get into the body through a crack in the epidermis, for example, erosion, scratch, lesion, surgical procedure, and Foley catheters and give rise to infections [3]. One of the most key reasons for MRSA evolution is redundant and wide ranging antibiotic overuse for less severe infections These MRSA isolates which are susceptible only to glycopeptides antibiotics such as vancomycin are becoming multidrug resistant (MDR) [8]. The rise in the number of MDR strains has led to a renewed curiosity in the utilization of macrolide (e.g., erythromycin)-lincosamide (e.g., clindamycin)-streptogramin B (e.g., quinupristin/dalfopristin) (collectively called as MLSB family) antibiotics to treat S. aureus infections with clindamycin being the favorable agent because of its superb pharmacokinetic properties [9]
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