# Genomic population structure, antimicrobial susceptibility, and clinical features of Mycobacterium xenopi isolates, Frankfurt, Germany, 1995–2020

## TL;DR

This study analyzed M. xenopi isolates from Germany to understand their genetic structure, drug resistance, and clinical relevance, finding clusters that suggest long-term transmission.

## Contribution

The study provides the largest genomic dataset of M. xenopi to date and identifies hospital-associated transmission clusters and drug susceptibility patterns.

## Key findings

- Only 26.5% of patients met criteria for clinically relevant NTM-PD.
- Three large hospital-associated clusters persisted for over 18 years.
- Clofazimine and most guideline drugs showed good in vitro efficacy, except rifampicin.

## Abstract

Mycobacterium xenopi causes non-tuberculous mycobacterial pulmonary disease (NTM-PD) that is difficult to treat. However, data on the genomic population structure, antimicrobial susceptibility, and the clinical significance of this pathogen remain scarce. We analyzed 76 clinical M. xenopi isolates from 70 patients collected between 1995 and 2020 in Frankfurt am Main, Germany. All isolates underwent phenotypic drug susceptibility testing and whole-genome sequencing. Cluster analysis, including isolates from this study and all hitherto available high-quality M. xenopi genome data sets in the Sequence Read Archive (n = 11), was performed by core genome multilocus sequence typing. In our cohort, only 26.5% of patients met criteria for clinically relevant NTM-PD. Phylogenetic analysis identified three large hospital-associated clusters (≤10 allelic difference), each involving between 7 and 20 patients and persisting for over 18 years, suggesting prolonged transmission chains or a common environmental source. We also defined three major clades (≤50 allelic difference), two of which contained isolates from the United Kingdom. Clofazimine and guideline-recommended antimycobacterial agents showed good in vitro efficacy, except rifampicin, with 23.6% resistance. This study represents a major expansion of M. xenopi genomic resources and provides insights into the genomic population structure, phenotypic susceptibility, and clinical characteristics of M. xenopi. Guideline-recommended antimycobacterials show good in vitro activity, while clofazimine may be a valuable addition to M. xenopi therapy. The identified clusters underscore the need for further investigation into transmission dynamics and globally successful clones.

Mycobacterium xenopi is an increasingly recognized opportunistic lung pathogen that is difficult to treat. Infections often occur in patients with pre-existing health conditions and can present substantial diagnostic and therapeutic challenges. A deeper understanding of its genetic diversity and resistance mechanisms is essential for optimal patient management and for clarifying potential transmission routes. By analyzing 76 whole-genome sequences together with detailed clinical information and phenotypic drug-susceptibility data, this study substantially expands the available genomic repertoire for M. xenopi. While clinical relevance was limited in our cohort, most guideline-recommended antimicrobial agents showed good efficacy in vitro. The detection of closely related strains might point toward a common environmental source of infection. These findings highlight the need for continued surveillance and provide a comprehensive foundation that supports more accurate monitoring, improved understanding of disease behavior, and future investigations into M. xenopi pathogenicity.