Clonal Diversification and Changes in Lipid Traits and Colony Morphology in Mycobacterium abscessus Clinical Isolates

Abstract

fThe smooth-to-rough colony morphology shift in Mycobacterium abscessus has been implicated in loss of glycopeptidolipid (GPL), increased pathogenicity, and clinical decline in cystic fibrosis (CF) patients. However, the evolutionary phenotypic and genetic changes remain obscure. Serial isolates from nine non-CF patients with persistent M. abscessus infection were characterized by colony morphology, lipid profile via thin-layer chromatography and matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS), sequencing of eight genes in the GPL locus, and expression level of fadD23, a key gene involved in the biosynthesis of complex lipids. All 50 isolates were typed as M. abscessus subspecies abscessus and were clonally related within each patient. Rough isolates, all lacking GPL, predominated at later disease stages, some showing variation within rough morphology. While most (77%) rough isolates harbored detrimental mutations in mps1 and mps2, 13% displayed previously unreported mutations in mmpL4a and mmpS4, the latter yielding a putative GPL precursor. Two isolates showed no deleterious mutations in any of the eight genes sequenced. Mixed populations harboring different GPL locus mutations were detected in 5 patients, demonstrating clonal diversification, which was likely overlooked by conventional acid-fast bacillus ( MABSC causes serious chronic pulmonary infections in those with underlying conditions such as bronchiectasis or cystic fibrosis (CF). In the United States and some other parts of the world, it is the second most frequent pulmonary nontuberculous mycobacterial (NTM) infection (28%), after Mycobacterium avium complex, and its prevalence is increasing (6, 7). MABSC causes significant mortality in the CF population. In Scandinavian countries, one-fourth of CF patients who have persistently positive MABSC sputum cultures have received lung transplantation or died (8).Glycopeptidolipid (GPL) is the most abundant glycolipid in the outer cell envelope of MABSC, and its synthesis and transport are controlled by the GPL locus (9). A growing number of studies have linked the rough colony morphology in MABSC to loss of GPL, increased pathogenicity, and clinical decline in CF patients (10)(11)(12)(13)(14)(15)(16). While most studies of persistent MABSC infection focused on CF patients, less is known about MABSC in the non-CF population regarding presence of mixed populations, clonal relatedness, and phenotypic and genotypic changes of strains collected over time.We have very limited understanding of the evolutionary phenotypic and genetic changes occurring in MABSC during persistent human lung infection. We lack the fundamental knowledge needed to identify selective pressures associated with rough morphology and, once identified, how to reverse them. To address these questions, we collected serial clinical isolates of M. abscessus from non-CF patients with persistent pulmonary infection who were followed for 5 years or more and assessed strain relatedness and diversity, colony...

Insights into the smooth‐to‐rough transitioning in Mycobacterium bolletii unravels a functional Tyr residue conserved in all mycobacterial MmpL family members

“…Importantly, mutations abrogating MmpL4a activity, such as the one described here, are of clinical relevance. Indeed, a recent study reporting the evolutionary phenotypic and genetic changes in serial isolates from patients infected with M. abscessus identified detrimental single point mutations in mmpL4a , leading either to a premature stop codon or to a frameshift mutation (Park et al ., ). Interestingly, these mutations in MmpL4a, also leading to the loss of GPL, occurred essentially during the chronic lung infection with M. abscessus (Park et al ., ).…”

MAB_3551c encodes the primary triacylglycerol synthase involved in lipid accumulation in Mycobacterium abscessus

“…While several studies have been published on TAG accumulation in M. tuberculosis, very little is known about this process in NTM for which only a few studies have focused on the model rapid-growing species M. smegmatis (Garton et al, 2002;Dhouib et al, 2011). However, a recent study reported the increased TAG production and accumulation in clinical M. abscessus strains isolated from CF patients suffering from a longer period of lung infection as compared to those suffering from a shorter period (Park et al, 2015). This observation allowed the authors to propose that TAG accumulation may be a phenotype associated with the long-term survival of M. abscessus in infected patients.…”

Mechanistic insight into mycobacterial MmpL protein function

“…Whole genome sequencing uncovered a mutation in the mmpL4a gene, which led to the substitution Tyr842His. In M. abscessus , a similar mutation was described recently (Park et al ., ). In M. abscessus , and also in M. bolletii , mmpL4 is part of the gene cluster responsible for the biosynthesis and transport of surface‐associated glycopeptidolipids (GPL) (Ripoll et al ., ).…”