Evaluation of Antimicrobial Susceptibilities of Rapidly Growing Mycobacteria

Abstract

Infections related to the rapidly growing mycobacteria (RGM), which are common in the environment, have clinical significance as they can affect both immunocompromised and immunocompetent patients. Treatment of RGM related infections is difficult, because they are resistant to many of the first-line tuberculosis agents, require a long-term multiple drug regimen, which is costly, and is associated with drug-related toxicities. The aim of this study was to investigate the in vitro antimicrobial susceptibility profiles of RGM isolated in Dokuz Eylül University Hospital and also to reveal epidemiological data. A total of 58 isolates [(Mycobacterium fortuitum (n= 35), Mycobacterium abscessus (n= 19) and Mycobacterium chelonae (n= 4)], which were isolated in Dokuz Eylül University Hospital between 2013 and 2018, were subjected to in vitro testing for nine antimicrobial agents (amikacin, cefoxitin, ciprofloxacin, clarithromycin, doxycycline, imipenem, linezolid, moxifloxacin and tobramycin) with the broth microdilution method recommended by the Clinical and Laboratory Standards Institute (CLSI). For M.abscessus; 73.68% of the isolates were found susceptible to amikacin; 73.68% of isolates were susceptible to clarithromycin at early reading and only 21.05% of them remained susceptible at late reading time. No resistance to imipenem were observed. M.abscessus isolates were highly resistant to tobramycin, doxycycline and fluoroquinolones. Antibiotic susceptibility testing of M.chelonae isolates demonstrated 100% susceptibility for amikacin, clarithromycin and tobramycin. No resistance to linezolid, imipenem and moxifloxacin were observed. None of the isolates were susceptible to cefoxitin. Ciprofloxacin and doxycycline also showed poor in vitro activity against M.chelonae isolates. For M.fortuitum clarithromycin susceptibility decreased from 32.35% to 2.94% after an additional incubation until 14 days. All tested isolates of the M.fortuitum were susceptible to amikacin, ciprofloxacin and moxifloxacin. None of the M.fortuitum isolates exhibited resistance to cefoxitin and imipenem. Most of the M.fortuitum isolates were resistant to tobramycin and doxycycline. When the results were evaluated together, RGM isolates in this study were highly susceptible to amikacin; and were highly resistant to doxycycline. In conclusion, this study supported that the status of antimicrobial susceptibilities were different between species and also showed the importance for hospitals to know susceptibility patterns of isolates in their region. It should be noted that accurate species determination is critical for treatment as well as susceptibility status of rapidly growing mycobacteria to the antimicrobials in use.