RAPMYCO: Mitigating conventional broth microdilution woes

Aim: Nontuberculous mycobacteria (NTM) are proven pathogens causing a plethora of diseases in humans. Various methods are available for their identification and susceptibility testing. Since their susceptibility varies with species, it becomes imperative to perform drug susceptibility testing. Various methods are available, of which broth microdilution is recommended by the Clinical and Laboratory Standards Institute (CLSI). We report our results after using RAPMYCO, commercially available, predosed, ready-to-use broth-microdilution plate. Materials and Methods: A total of 33 isolates of NTM were tested using the RAPMYCO panel for susceptibility against amikacin, cefoxitin, ciprofloxacin, clarithromycin, doxycycline, imipenem, linezolid, trimethoprim + sulfamethoxazole, tobramycin, and tigecycline, and the results were interpreted as per the CLSI guidelines. Results and Conclusion: Minimum inhibitory concentration results of conventional broth microdilution correlated well with those of RAPMYCO. All Mycobacterium fortuitum and Mycobacterium chelonae isolates were susceptible to amikacin and tobramycin.Good susceptibility was observed towards clarithromycin for all isolates; some degree of susceptibility was observed for quinolones and linezolid. High degree of resistance was seen for cefoxitin, doxycycline, and trimethoprim + sulfamethoxazole. Mycobacterium abscessus was the most resistant. RAPMYCO was simple, easy, and saved precious person-hours as compared to conventional broth microdilution.