Gerrit Brandis1, Diarmaid Hughes. 1. Department of Medical Biochemistry and Microbiology, Box 582 Biomedical Center, Uppsala University, Uppsala, Sweden.
Abstract
OBJECTIVES: The evolution of rifampicin resistance in Mycobacterium tuberculosis is a major threat to effective tuberculosis therapy. Much is known about the initial emergence of rifampicin resistance, but the further evolution of these resistant strains has only lately been subject to investigation. Although resistance can be caused by many different mutations in rpoB, among clinical M. tuberculosis isolates the mutation rpoB S531L is overwhelmingly the most frequently found. Clinical isolates with rpoB S531L frequently carry additional mutations in genes for RNA polymerase subunits, and it has been speculated that these are fitness-compensatory mutations, ameliorating the fitness cost of the primary resistance mutation. We tested this hypothesis using Salmonella as a model organism. METHODS: We created the rpoB S531L mutation in Salmonella and then evolved independent lineages with selection for mutants with increased relative fitness. Relative fitness associated with putative compensatory mutations was measured after genetic reconstruction in isogenic strains. RESULTS: Compensatory mutations were identified in genes coding for different subunits of RNA polymerase: rpoA, rpoB and rpoC. Genetic reconstructions demonstrated that each of these secondary mutations reduced the fitness cost of the rpoB S531L resistance mutation. CONCLUSIONS: The compensatory mutations identified in Salmonella cluster in similar locations to the additional mutations found in M. tuberculosis isolates. These new data strongly support the idea that many of the previously identified rpoA, rpoB and rpoC mutations in rifampicin-resistant M. tuberculosis (rpoB S531L) are indeed fitness-compensatory mutations.
OBJECTIVES: The evolution of rifampicin resistance in Mycobacterium tuberculosis is a major threat to effective tuberculosis therapy. Much is known about the initial emergence of rifampicin resistance, but the further evolution of these resistant strains has only lately been subject to investigation. Although resistance can be caused by many different mutations in rpoB, among clinical M. tuberculosis isolates the mutation rpoB S531L is overwhelmingly the most frequently found. Clinical isolates with rpoB S531L frequently carry additional mutations in genes for RNA polymerase subunits, and it has been speculated that these are fitness-compensatory mutations, ameliorating the fitness cost of the primary resistance mutation. We tested this hypothesis using Salmonella as a model organism. METHODS: We created the rpoB S531L mutation in Salmonella and then evolved independent lineages with selection for mutants with increased relative fitness. Relative fitness associated with putative compensatory mutations was measured after genetic reconstruction in isogenic strains. RESULTS: Compensatory mutations were identified in genes coding for different subunits of RNA polymerase: rpoA, rpoB and rpoC. Genetic reconstructions demonstrated that each of these secondary mutations reduced the fitness cost of the rpoB S531L resistance mutation. CONCLUSIONS: The compensatory mutations identified in Salmonella cluster in similar locations to the additional mutations found in M. tuberculosis isolates. These new data strongly support the idea that many of the previously identified rpoA, rpoB and rpoC mutations in rifampicin-resistant M. tuberculosis (rpoB S531L) are indeed fitness-compensatory mutations.
Authors: Morten O A Sommer; Christian Munck; Rasmus Vendler Toft-Kehler; Dan I Andersson Journal: Nat Rev Microbiol Date: 2017-07-31 Impact factor: 60.633
Authors: Taeksun Song; Yumi Park; Isdore Chola Shamputa; Sunghwa Seo; Sun Young Lee; Han-Seung Jeon; Hongjo Choi; Myungsun Lee; Richard J Glynne; S Whitney Barnes; John R Walker; Serge Batalov; Karina Yusim; Shihai Feng; Chang-Shung Tung; James Theiler; Laura E Via; Helena I M Boshoff; Katsuhiko S Murakami; Bette Korber; Clifton E Barry; Sang-Nae Cho Journal: Mol Microbiol Date: 2014-02-26 Impact factor: 3.501