Inducible Clindamycin Resistance in Gram Positive Isolates Obtained from Clinical Samples in a Tertiary Care Hospital in Mumbai

Abstract

Background: Infections by Gram positive isolates are increasing due to which their antibiotic sensitivity pattern is changing. This has revived interest in Macrolide-Lincosamide Streptogramin Group B (MLSB) antibiotics. Misuse of MLSB antibiotics has increased resistance in Gram-positive organisms especially Staphylococcus species to these drugs. Clindamycin is an important drug for treatment of Gram-positive isolates. Hence detection of inducible clindamycin resistance in these clinical isolates is required to prevent therapeutic failure and avoid inadvertent use of this drug. Aim and Objectives: To detect inducible clindamycin resistance among Gram positive isolates obtained from clinical samples. Material and Methods: The study was carried out over a period of one year (Jan-Dec 2018). A total of 461 Gram positive isolates of Staphylococcus species, Streptococcus pneumoniae and Beta-haemolytic Streptococcus were identified from various clinical samples and antibiotic susceptibility done on Vitek2 Compact using GP ID, and 628 and ST01 cards respectively. According to CLSI 2017, D-zone test was performed for detection of inducible clindamycin resistance for strains resistant to erythromycin. Results: Staphylococcus aureus (SA) isolates were 59%, Staphylococcus epidermidis (SE) 21%, other Coagulase Negative Staphylococcus (CONS) 16%, Streptococcus pyogenes (Group A-beta haemolytic) 2%, Streptococcus agalactiae (Group B betahaemolytic) 1% and Streptococcus pneumoniae (alpha haemolytic) 1%. Isolates of Methicillin Sensitive Staphylococcus aureus (MSSA) were 58% and Methicillin Resistant Staphylococcus aureus (MRSA) were 42%. Frequencies of MS (clindamycin sensitive) phenotypes, inducible clindamycin resistance (MLSBi) phenotypes and phenotypes showing constitutive resistance (MLSBc) were 44%, 12% and 3% respectively among MSSA and 34%, 39% and 8% respectively among MRSA. Among SE, MS, MLSBc and MLSBi phenotypes were 39%, 24% and 12% respectively and 8%, 44% and 30% respectively among other CONS. One isolate of S. pyogenes was of MLSBi phenotype and none among S. agalactiae and S. pneumoniae. Conclusion: The study emphasizes the significance of conducting D-zone test along with routine antimicrobial susceptibility testing to guide in therapy and avoid treatment failures.

Keywords

• D-zone test
• Gram Positive Isolates
• Inducible Clindamycin Resistance