High Rates of Antimicrobial Resistance in Rapidly Growing Mycobacterial Infections in Taiwan

Abstract

Rapidly growing mycobacteria (RGM) has gained increasing clinical importance, and treatment is challenging due to diverse drug resistance. The minimum inhibitory concentrations (MIC) of 13 antimicrobial agents using modified broth microdilution and E-test were determined for 32 clinical isolates of RGM, including Mycobacterium abscessus (22 isolates) and Mycobacterium fortuitum (10 isolates). Our results showed high rates of resistance to available antimicrobial agents. Amikacin remained highly susceptible (87.5%). Clarithromycin was active against the isolates of M. abscessus (95.5%), and M. fortuitum (50%), but 36.4% and 20% had inducible macrolide resistance, respectively. Rates of susceptibility to tigecycline were 68.2–70%, and linezolid 45.5–50%, respectively. The quinolones (ciprofloxacin and moxifloxacin) showed better in vitro activity against M. fortuitum isolates (50% susceptibility) than the M. abscessus isolates (31.8% susceptibility). The susceptibilities to other conventional anti-mycobacterial agents were poor. The MICs of E-test were higher than broth microdilution and may result in reports of false resistance. In conclusion, the implementation of the modified broth microdilution plates into the routine clinical laboratory workflow to provide antimicrobial susceptibility early, allows for the timely selection of appropriate treatment of RGM infections to improve outcome.

Mechanisms of Linezolid Resistance in Mycobacteria

“…Among patients in the United Kingdom, resistance had been detected in 51.7% (30/58) and 54.2% (13/24) of M. abscessus and M. chelonae isolates, respectively [48]. In China, Ye et Institute), the resistance rates for the same isolates increased to 90.9% for M. abscessus and 70.0% for M. fortuitum [51], a stark reminder of how MIC results could be affected by the method used to determine them.…”

“…With broth microdilution, they detected resistance in 45.5% (10/22) of M. abscessus isolates and 12.5% (1/8) of M. fortuitum isolates. However, with the Etest (not endorsed by the European Committee on Antimicrobial Susceptibility Testing and Clinical and Laboratory Standards Institute), the resistance rates for the same isolates increased to 90.9% for M. abscessus and 70.0% for M. fortuitum [ 51 ], a stark reminder of how MIC results could be affected by the method used to determine them.…”