title: Nonmutational compensation of the fitness cost of antibiotic resistance in mycobacteria by overexpression of tlyA rRNA methylase.
abstract: Several studies over the last few decades have shown that antibiotic resistance mechanisms frequently confer a fitness cost and that these costs can be genetically ameliorated by intra- or extragenic second-site mutations, often without loss of resistance. Another, much less studied potential mechanism by which the fitness cost of antibiotic resistance could be reduced is via a regulatory response where the deleterious effect of the resistance mechanism is lowered by a physiological alteration that buffers the mutational effect. In mycobacteria, resistance to the clinically used tuberactinomycin antibiotic capreomycin involves loss-of-function mutations in rRNA methylase TlyA or point mutations in 16S rRNA (in particular the A1408G mutation). Both of these alterations result in resistance by reducing drug binding to the ribosome. Here we show that alterations of tlyA gene expression affect both antibiotic drug susceptibility and fitness cost of drug resistance. In particular, we demonstrate that the common resistance mutation A1408G is accompanied by a physiological change that involves increased expression of the tlyA gene. This gene encodes an enzyme that methylates neighboring 16S rRNA position C1409, and as a result of increased TlyA expression the fitness cost of the A1408G mutation is significantly reduced. Our findings suggest that in mycobacteria, a nonmutational mechanism (i.e., gene regulatory) can restore fitness to genetically resistant bacteria. Our results also point to a new and clinically relevant treatment strategy to combat evolution of resistance in multidrug-resistant tuberculosis. Thus, by utilizing antagonistic antibiotic interactions, resistance evolution could be reduced.
authors.affiliation: Institute of Medical Microbiology, University of Zurich, CH-8006 Zurich, Switzerland.
authors.forename: Pietro
authors.initials: P
authors.lastname: Freihofer
authors.affiliation: Institute of Medical Microbiology, University of Zurich, CH-8006 Zurich, Switzerland.
authors.forename: Rashid
authors.initials: R
authors.lastname: Akbergenov
authors.affiliation: Institute of Medical Microbiology, University of Zurich, CH-8006 Zurich, Switzerland.
authors.forename: Youjin
authors.initials: Y
authors.lastname: Teo
authors.affiliation: Institute of Medical Microbiology, University of Zurich, CH-8006 Zurich, Switzerland.
authors.forename: Reda
authors.initials: R
authors.lastname: Juskeviciene
authors.affiliation: Department of Medical Biochemistry and Microbiology, Uppsala University, Box 582, SE-751 23 Uppsala, Sweden.
authors.forename: Dan I
authors.initials: DI
authors.lastname: Andersson
authors.affiliation: Institute of Medical Microbiology, University of Zurich, CH-8006 Zurich, Switzerland.
authors.forename: Erik C
authors.initials: EC
authors.lastname: Böttger
mesh_terms: D001426:Bacterial Proteins / Q000235:genetics*; D002474:Cell-Free System; D024881:Drug Resistance, Bacterial / Q000235:genetics*; D009154:Mutation; D009161:Mycobacterium / Q000187:drug effects* / Q000201:enzymology / Q000235:genetics; D014176:Protein Biosynthesis; D012336:RNA, Ribosomal, 16S / Q000378:metabolism; D012338:RNA, Ribosomal, 23S / Q000378:metabolism
chemical_list: D001426:Bacterial Proteins; D012336:RNA, Ribosomal, 16S; D012338:RNA, Ribosomal, 23S; C112817:TlyA protein, Mycobacterium tuberculosis
keywords: Mycobacterium tuberculosis; antibiotic resistance; compensation; fitness; rRNA methylation; tlyA