Antibiotic susceptibility pattern of rapidly growing mycobacteria

Background : The rapidly growing mycobacteria (RGM) causing human infections primarily consist of the Mycobacterium fortuitum group, Mycobacterium abscessus and Mycobacterium chelonae. The antibiotic susceptibility testing is important to determine the appropriate therapy as the antibiotics used to treat RGM are different from those used for treating infections caused by slow growers of mycobacteria. Aim : To determine antibiotic susceptibility of RGM using Kirby Bauer method and following Clinical and Laboratory Standards Institute (CLSI) guidelines. Settings and Design : Larsen and Toubro Microbiology Research Centre, Vision Research Foundation, Sankara Nethralaya, Chennai, Retrospective study. Materials and Methods : The antibiotic susceptibility testing was performed following CLSI method for the drugs Amikacin, Azithromycin, Tobramycin, Ceftazidime, Cephotaxime, Cefuroxime, Cefaperazone, Ceftriaxone, Ciprofloxacin, Ofloxacin, Norfloxacin, Gatifloxacin and Moxifloxacin. Results and Conclusions : Out of the 148 RGM isolates 146 (98) were susceptible to amikacin, 138 (91) to gatifloxacin, 132 (87) to moxifloxacin, 122 (76) to ciprofloxacin and 116 (74) to Norfloxacin. Majority of the RGM were resistant to Ceftazidime, Cephotaxime and Cefaperazone. All the M. abscessus isolates were resistant to tobramycin. The in vitro antibiotic susceptibility testing by disc diffusion method showed that majority of the RGM were sensitive to Amikacin followed by Gatifloxacin, Moxifloxacin and Ciprofloxacin.