Emergence of plasmid-borne erm(55)-associated macrolide resistance in Mycobacterium chelonae and other rapidly-growing non-tuberculous mycobacteria in Europe

Macrolides are key agents for treating infections caused by non-tuberculous mycobacteria (NTM). Nevertheless, chromosomal erm genes conferring inducible macrolide resistance are described in some NTM species, such as Mycobacterium abscessus and M. fortuitum, whereas M. chelonae had long been considered as lacking a functional erm. Recent descriptions from the USA and Japan of a new plasmid-borne erm(55) (erm(55)P) in M. chelonae and other rapidly growing mycobacteria (RGM) have challenged this assumption. We investigated erm(55)P occurrence in clinical RGM referred to the French National Reference Centre for Mycobacteria between 2012 and 2026 by genome screening and erm(55)P specific real-time PCR. Positive isolates underwent long-read whole genome sequencing (GridIon, Oxford Nanopore Technologies). Clarithromycin (CLR) minimum inhibitory concentration (MIC) was determined by broth microdilution (RAPMYCO and FRATMYC, Thermo Fisher) and read up to 14 days. Five clinical isolates showing inducible CLR resistance (MIC range <0.25-64 mg/L on day 3-4 and 128 - >128 mg/L on day 14) were positive for erm(55)P: one M. chelonae, three M. neoaurum, and one M. parafortuitum. erm(55)P-positive M. chelonae genomes from this and previous descriptions did not cluster together in the phylogenetic analysis of 263 genomes. The assembled plasmids showed high similarity to previously reported erm(55)-carrying plasmids, especially within the erm(55)P region. The upstream sequence of erm(55)P showed a secondary structure compatible with a possible translation attenuation mechanism. These findings document the first report of a plasmid-borne erm(55) in Europe in M. chelonae and other RGM and raise concern about the emergence of plasmid macrolide resistance in NTM.