INDUCIBLE CLINDAMYCIN RESISTANCE AND METHICILLIN RESISTANCE AMONGST STAPHYLOCOCCUS AUREUS ISOLATES: A PHENOTYPIC DETECTION

Abstract

Background: Increasing prevalence of Methicillin resistant staphylococcus aureus is global public health issue in both community and hospital settings. Management of MRSA infections is tough owing to its resistance to many antibiotics. Macrolide-lincosamide-streptogramins B (MLS_B) antibiotics are commonly used for the management of MRSA. Clindamycin is being the preferred agent due to its excellent pharmacokinetic properties. However, use of clindamycin in erythromycin resistant Staphylococcus isolates could result in treatment failure as a result of inducible clindamycin resistance in spite of showing in vitro sensitivity.

Aim: This study was aimed to find out the percentage of S. aureus having inducible clindamycin resistance (iMLS_B) in our geographic area using D-test and to ascertain the relationship between methicillin-resistant S. aureus (MRSA) and inducible clindamycin resistance.

Methods: A total of 822 Staphylococcus aureus isolated from different clinical samples were subjected to routine antibiotic sensitivity testing by Kirby Bauer disc diffusion method. All isolates were tested for Methicillin resistance by using cefoxitin 30 µg discs. Inducible clindamycin resistance was detected by ‘D’ test as per CLSI guidelines.

Results: Out of the 822 Staphylococcus aureus isolates, 395 (48.05%) were MRSA and 427 (51.94%) were MSSA. 482 (58.63%) isolates were erythromycin resistant. These erythromycin resistant isolates when subjected to ‘D’ test, 89 isolates showed MS phenotype, 148 showed inducible MLS_B phenotype and 245 showed Constitutive MLS_B phenotype. Out of 395 MRSA isolates 116 (29.36%) showed Inducible MLS_B phenotype and 190 (48.10%) showed Constitutive MLS_B phenotype, while in 427 methicillin sensitive Staphylococcal isolates 32(7.49%) showed Inducible MLSB phenotype and 55 (12.88%) showed Constitutive MLS_B phenotype. The percentage of inducible and constitutive resistance was higher amongst MRSA isolates as compared to MSSA isolates.

Conclusion: Considering the higher prevalence of clindamycin resistance in MRSA isolates as compared MSSA isolates, routine D- test of S.aureus isolates is strongly recommended to prevent treatment failure. Therefore inducible clindamycin resistance detection should be the part of S.aureus sensitivity testing in all the microbiology

laboratories.