Open Collections

Pichler, Virginia

University of British Columbia

Mycobacterium abscessus (MABS) exhibits resistance mechanisms that share features with Mycobacterium tuberculosis, yet gaps remain in understanding the phenotypic and genotypic aspects of persistent infections. The transition from smooth (S) to rough (R) morphotypes, primarily regulated by the glycopeptidolipid (GPL) gene locus, is associated with reduced GPL levels and increased virulence. In the R morphotype, bacteria form cords that help them evade the host immune response, leading to infection persistence. This study paired culture-based and molecular methods to elucidate the relationship between phenotypic characteristics and genetic determinants in clinical MABS strains isolated from 19 long-term cystic fibrosis patients in Vancouver, Canada. Strains were analyzed using antibiotic testing, lipid analysis, infection modeling and whole-genome sequencing (WGS). Deviations from the previously described S and R morphotypes discrete morphologies were observed, with heterogenous populations found in half of clinical strains. Lipid analysis confirmed GPL profiles matched the assigned morphotypes, except in seven strains that expressed GPL yet were classified as R. A subset of 25 strains from five patients was evaluated for bacterial growth during infection of THP-1 macrophages. Notably, a morphotype transition from S to R was observed in three patients with declining lung function. Contrary to prior observations with reference strains, the R isolates replicated significantly faster than the S isolates in the macrophage infection model. Importantly, the results of the ex vivo macrophage growth assay reliably predicted lung function stability or decline in isolates collected over the course of chronic infections. This study is the first to directly quantify intracellular replication rates and correlate them with pulmonary deterioration. Through the analysis of isogenic pairs and serial isolates, the inherent plasticity of rough strains within and between patients is underscored, manifesting in variable replication rates and increasing drug resistance in later-stage isolates. While the study confirmed the correlation between morphotype and GPL levels, it unveiled greater variability within morphotype groups than previously recognized, particularly during intracellular infection. These findings contribute to the expanding knowledge base surrounding MABS infections, offering insights that can inform future research, diagnostic methodologies, and treatment approaches.

Text

2025-01-17

Attribution-NonCommercial-NoDerivatives 4.0 International

http://hdl.handle.net/2429/90145

Microbiology and Immunology

University of British Columbia

UBCV

http://creativecommons.org/licenses/by-nc-nd/4.0/