Antimicrobial susceptibility testing of rapidly growing mycobacteria isolated from cases of surgical site infections by microbroth dilution method at a Tertiary Care Center

Abstract

Aim: The study was carried out to ascertain antimicrobial susceptibility pattern of rapidly growing mycobacteria (RGM) isolated from cases of surgical site infections from May 2013 to May 2014 at a tertiary care center in Pune. Materials and Methods: This study included the isolation of RGM from surgical site infections from May 2013 to May 2014 at a tertiary care center in Pune. The specimens were processed for microscopy (Ziehl–Neelsen stain) and culture (Lowenstein–Jensen media) using conventional methods. The minimum inhibitory concentrations of each of the isolates were determined by microbroth dilution, using Sensititre™ RAPMYCO manufactured by the firm TREK Diagnostic Systems from Thermo Scientific. Interpretations of results were done as per the Clinical and Laboratory Standards Institute M24-A. Results: Of the RGM isolated, Mycobacterium abscessus was the predominant isolate followed by Mycobacterium fortuitum and Mycobacterium chelonae. Of the 102 isolates, 64 (53.3%) were M. abscessus, 30 (25%) were M. fortuitum, 8 (6.67%) were M. chelonae, and 18 (15%) were other atypical Mycobacterium species. All 102 isolates of RGM were tested for antibiotic susceptibility testing by microbroth dilution. M. fortuitum and M. chelonae were sensitive to most of the antibiotics tested with few exceptions. All isolates (M. fortuitum and M. chelonae) were resistant to cefoxitin except few M. abscessus. Maximum resistance was seen with M. abscessus and they were sensitive to amikacin, tobramycin, tigecycline, and clarithromycin only. Out of 64 isolates, 32 (50%) were resistant to linezolid and imipenem. Conclusions: This study was carried out to highlight the importance of RGM and their susceptibility testing in all clinical microbiology laboratories.