INDUCIBLE CLINDAMYCIN RESISTANT STAPHYLOCOCCUS AUREUS ISOLATES FROM TERTIARY CARE HOSPITAL, BETTIAH, INDIA

Abstract

BACKGROUND Staphylococcus aureus is a frequent cause of bacterial infections in both developed and developing countries. The Clinical and Laboratory Standards Institute (CLSI) recommends D-test, which is a phenotypic screening method for inducible Clindamycin resistance. Therefore, all erythromycin resistant S. aureus should be tested for inducible Clindamycin resistance to prevent Clindamycin treatment failures and to report prevalence resistant phenotypes which varies widely. MATERIALS AND METHODS This cross-sectional study was conducted for a period of one year from January 2017 to January 2018. We analysed 125 non-duplicate consecutive isolates of S. aureus isolated from various clinical specimens like pus, wound swab, aspirates, blood and sterile fluids. A total of 125 S. aureus isolates derived from wound infection were evaluated for antimicrobial susceptibility testing by Kirby-Bauer disk diffusion method. Methicillin Resistance was detected using Cefoxitin (30 mu g) disk and inducible Clindamycin resistance was determined in all erythromycin resistant isolates by using D-zone test. RESULTS Out of 125 S. aureus isolates of the MRSA 46 (36.6%) were derived from respective Pus samples 19 (41.53%), the S. aureus isolates derived from Wound samples were MRSA 8 (18.03%), the S. aureus isolates derived from Blood samples were MRSA 10 (22.40%), the S. aureus isolates derived from Miscellaneous samples were MRSA 6 (13.66%) and the S. aureus isolates derived from urine samples were MRSA 2 (3.75%). A total of 26 S. aureus isolates showed inducible Clindamycin resistance by giving a positive D-zone test; hence, its prevalence was found to be 21.00% (26/125) with percentage distribution of cMLSB phenotype and MS phenotypes in all S. aureus isolates as 19.4% and 24.6% respectively. The susceptible phenotype (E-S and CD-S) predominated in MSSA (39.75%) as compared to MRSA (13.11%). Whereas, the constitutive resistant (cMLSB) predominated in MRSA (50.27%) as compared to MSSA (15.46%). Both the MS phenotype and the inducible resistant (iMLSB) phenotypes predominated in MSSA (19.87 and 24.92%, respectively) as compared to MRSA (22.40% and 14.20%, respectively). The antimicrobial susceptibility test result of all the 105 S. aureus isolates with iMLSB phenotype revealed that they were 100% sensitive to Vancomycin and Linezolid with moderate sensitivity (71.14%) to Gentamicin, Cefuroxime and least sensitivity (23.81%) to Doxycycline and 20.95% to Ciprofloxacin. CONCLUSION Due to high prevalence of Erythromycin resistance amongst S. aureus isolates, we suggest that D-zone test should be routinely done in all laboratories for appropriate prescription of Clindamycin and thereby preventing emergence of inducible resistant strains and treatment failure.