Abstract
BackgroundStaphylococcus aureus, an important nosocomial pathogen, is frequently associated with infections in human. 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. Macrolide-lincosamide streptogramin B family of antibiotics is commonly used to treat such infections as an alternative to vancomycin.MethodsThis study was conducted over the period of one and half year from November 2013–April 2015 in Microbiology laboratory of Nepal Medical College and Teaching Hospital, Kathmandu, Nepal to find the incidence of different phenotypes of MLSB resistance among S. aureus from clinical samples and their association with methicillin resistance. Two hundred seventy 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).ResultsOf the 270 clinical isolates of S. aureus, 25.1% (68/270) were MRSA. Erythromycin and clindamycin resistance was seen in 54.4% (147/270) and 41.8% (113/270) isolates respectively. Resistance to erythromycin and clindamycin were higher in MRSA as compared to MSSA (erythromycin-resistance: 88.2% Vs 39.1% and clindamycin-resistance: 79.4% Vs 41.8%). The overall prevalence of iMLSB and cMLSB phenotype was 11.48% (31/270) and 29.25% (79/270) respectively. Both iMLSB and cMLSB phenotypes predominated in MRSA strains.ConclusionsDetection rate of MRSA in our study shows the necessity to improve in healthcare practices and to formulate new policy for the control of MRSA infections. Clindamycin resistance in the form of iMLSB and cMLSB especially among MRSA emphasizes the need of D-test to be performed routinely in our set up while using clindamycin as an alternative choice to anti-staphylococcal antibiotics like vancomycin and linezolid in the treatment of staphylococcal infections.
Highlights
Staphylococcus aureus, an important nosocomial pathogen, is frequently associated with infections in human
To avoid clinical therapeutic failure in the resistance case mediated by erm gene, it is very important to detect inducible clindamycin resistance phenotypes in vitro which can be made by erythromycin-clindamycin disc approximation test (D-test) as its sensitivity was found 100% in different studies when compared with erm and msr gene detection by polymerase chain reaction [6,7,8]
Resistance to erythromycin and clindamycin were higher in methicillin resistant S. aureus (MRSA) as compared to methicillin susceptible S. aureus (MSSA) (E-R: 88.2% Vs 39.1% and Clin-R: 79.4% Vs 22.2%) (p value = 0.006) (Fig. 1)
Summary
Staphylococcus aureus, an important nosocomial pathogen, is frequently associated with infections in human. It is very difficult to detect the inducible clindamycin resistance in the routine laboratory as they appear erythromycin-resistant and clindamycin sensitive in vitro when not placed adjacent to each other. In such cases, in vivo therapy with clindamycin may select constitutive erm mutants leading to clinical therapeutic failure. In vivo therapy with clindamycin may select constitutive erm mutants leading to clinical therapeutic failure In case of another mechanism of resistance mediated through msrA genes i.e. efflux of antibiotic, staphylococcal isolates appear erythromycin-resistant and clindamycin-sensitive both in vivo and in vitro and the strain do not typically become clindamycin resistant during therapy [5]. This study was conducted to determine the prevalence of inducible clindamycin resistance among clinical S. aureus isolates and to study their association with MRSA in our set up
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