The Drug Susceptibility of Non-Tuberculous Mycobacteria (NTM) in a Referral Hospital in Rome from 2018 to 2023.

Background

The treatment of non-tuberculous mycobacterial (NTM) infections is challenging because of the difficulty in obtaining phenotypic (pDST) and/or molecular (mDST) drug susceptibility testing and the need of a multi-drug regimen.

Objectives

The objective was to describe the in vitro susceptibility patterns of various NTM species through an analysis of susceptibility results obtained on isolates collected between 2018 and 2023.

Methods

Species identification and mutations in rrs or rrl genes (mDST) were identified by a line probe assay, while the pDST was performed by broth microdilution and interpreted according to CLSI criteria.

Results

We analysed 337 isolates of NTM belonging to 15 species/subspecies. The Mycobacterium avium complex (MAC) was the most common (62%); other species identified included M. gordonae (11%), M. kansasii (5%), the M. abscessus complex (8%), M. chelonae (6%), and M. fortuitum (2%). The results of pDST (claritromycin and amikacin) and mDST (rrl and rrs genes) on 66 NTM strains showed that while wild-type rrl and rrs occurred in 86.3% and 94% strains, respectively, the pDST showed 88% sensitivity for clarithromycin and 57.5% for amikacin. The main incongruity was observed for macrolides.

Conclusions

Most NTM are likely to be susceptible to macrolides and aminoglycosides. The molecular identification of resistant genotypes is accurate and strongly recommended for optimal patient management.