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This study found that ethambutol resistance frequently develops before macrolide resistance in patients with Mycobacterium avium complex pulmonary disease. Among 16 patients who developed macrolide resistance during standard treatment, 44% acquired ethambutol resistance mutations before macrolide resistance emerged, and in vitro experiments confirmed that ethambutol-resistant strains required higher concentrations of macrolides to prevent resistance development. This pattern was particularly observed in patients without cavitary lung lesions.
Why it matters
The findings suggest that monitoring for ethambutol resistance during treatment could help predict and potentially prevent macrolide resistance, which is a critical concern since macrolides are the cornerstone of treatment for Mycobacterium avium complex infections. This could lead to modified treatment strategies that adjust therapy when ethambutol resistance is detected, before macrolide resistance develops.
⚠️ Preprint – Noch nicht peer-reviewed
Dieser Artikel wurde noch nicht von unabhängigen Experten begutachtet. Die Ergebnisse sind vorläufig und sollten mit Vorsicht interpretiert werden.
Objectives: To investigate whether ethambutol resistance in Mycobacterium avium complex is associated with the emergence of macrolide resistance. Methods: Patients who developed macrolide resistance during guideline-based treatment were included, and longitudinal analyses of minimum inhibitory concentrations and mutations in embB or the upstream region of embA were performed. Clinical, microbiological, and radiological characteristics were compared according to the mutation status of embB or embA upstream region, prior to the emergence of macrolide resistance. We further evaluated the impact of embB mutation on the development of macrolide resistance using in vitro time-kill assays. Results: Sixteen patients developed macrolide resistance during guideline-based treatment. None of these patients had an ethambutol minimum inhibitory concentration >=16 ug/mL or embB or embA upstream mutations at treatment initiation; however, 8/16 patients (50.0%) had an ethambutol minimum inhibitory concentration >=16 ug/mL at the time of macrolide resistance detection, and 7/16 (43.8%) had developed embB or embA upstream mutations prior to the emergence of macrolide resistance. Cavitary lesions were present in 1/7 (14.3%) patients with embB or embA upstream mutations. In strains with embB mutations, the minimum inhibitory concentration of ethambutol increased by 1-2 dilutions relative to that of pretreatment isolates, with a corresponding increase in the concentration required to suppress macrolide resistance. Conclusions: Ethambutol resistance may contribute to the development of macrolide resistance in patients with M. avium complex pulmonary disease, particularly in those without cavitary lesions.