Evaluation of antimicrobial susceptibilities of rapidly growing mycobacteria

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, drug therapy typically involves 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 Mycobacterium fortuitum, Mycobacterium abscessus and Mycobacterium chelonae isolates isolated in Dokuz Eylül University Hospital and to reveal epidemiological data. Total of 58 isolates included (35 M. fortuitum, 19 M. abscessus and four M. chelonae), which were isolated in Dokuz Eylul 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% (14/19) of the isolates were found susceptible to amikacin; %73.68 (14/19) of isolates were susceptible to clarithromycin the third day and only 21.05% (4/19) of them remained susceptible at day 14. No resistance to imipenem were observed in M. abscessus isolates. For M. fortuitum clarithromycin susceptibility decreased from %32.35 (11/34) to %2.94 (1/34) after an additional incubation until 14 days. All tested isolates of the M. fortuitum (n=35) were susceptible to amikacin, ciprofloxacin and moxifloxacin. None of the M. fortuitum isolates exhibited resistance to cefoxitin and imipenem. Antibiotic susceptibility testing of the four M. chelonae isolates demonstrated 100% susceptibility for amikacin, clarithromycin and tobramycin; none of the isolates were susceptible to cefoxitin. Both M. fortuitum, M. abscessus and M. chelonae isolates were highly susceptible to amikacin; and were highly resistance to doxycycline. In conclusion, our study supported that status of antimicrobial susceptibilities were different between species and also showed that 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.