Background: M. abscessus (Mab) is a highly antibiotic resistant opportunistic pathogen causing clinically challenging infections in patients with preexisting lung diseases or under immunosuppression. Hence, reliable antibiotic susceptibility data is required for effective treatment. Aims of this study were to investigate (i) the congruence of genotypic and phenotypic antimicrobial susceptibility testing, (ii) the relationship between resistance profile and clinical course, as well as (iii) the phylogenetic relations of Mab in a German patient cohort.
Materials/methods: A total of 39 isolates from 29 patients infected or colonized with Mab underwent genotypic and phenotypic drug susceptibility testing. Clinical data were correlated to susceptibility data. Phylogenetic analysis was performed by means of whole genome sequencing (WGS) and single nucleotide polymorphism (SNP) analysis.
Results: Macrolide resistance was mainly mediated by functional Erm (41) methyltransferases (T28 sequevars) in M. abscessus subsp. abscessus (n=25) and M. abscessus subsp. bolletii (n=2). It was significantly associated with impaired culture conversion (p=0.02). According to the core SNP phylogeny, we identified three clusters of closely related isolates with SNP distances below 25. Representatives of all circulating global clones (Absc. 1, Absc. 2 and Mass. 1) were identified in our cohort. However, we could not determine evidence for in-hospital interhuman transmission from clinical data.
Conclusions: In our patient cohort, we identified three Mab clusters with closely related isolates and representatives of the previously described international clusters, but no human-to-human in-hospital transmission. Macrolide and aminoglycoside susceptibility data are critical for therapeutic decision-making in Mab infections.