Portuguese in vitro antibiotic susceptibilities favor current nontuberculous mycobacteria treatment guidelines

Setting Nontuberculous mycobacteria (NTM) are increasingly recognized as causative agents of opportunistic infections in humans for which effective treatment is challenging. There is, however, very little information on the prevalence of NTM drug resistance in Portugal. Objective and Design Our aim was to analyze the drug susceptibility testing (DST) performed in NTM at the Portuguese National Health Institute Dr. Ricardo Jorge from February 2003 to February 2016. A total of 262 DST were included in the analysis. Results Most (94%) M. avium intracellulare complex isolates showed in vitro susceptibility to clarithromycin. All M. kansasii isolates were susceptible to rifampicin and ethambutol and 97.1% were susceptible to isoniazid. The majority of rapidly-growing mycobacteria (RGM) demonstrated in vitro susceptibility to amikacin, clarithromycin and cefoxitin. However, in RGM there was a marked increase on the relative risk of having sulfamethoxazole resistance in isolates resistant to ciprofloxacin compared to susceptible isolates. Conclusion Tested NTM in Portugal revealed in vitro susceptibility to most of the antimicrobials currently recommended for treatment. However, our results also suggest that sulfamethoxazole should be avoided in treatment of RGM resistant to ciprofloxacin (or vice versa). Further trials that correlate the in vitro DST results with the clinical outcome are needed in order to reach conclusions on efficient antimicrobial therapy.This research did not receive any specific grant from funding agencies in the public, commercial, or non-profit sectors