title: Mycobacterium tuberculosis Is Resistant to Isoniazid at a Slow Growth Rate by Single Nucleotide Polymorphisms in katG Codon Ser315.
abstract: An important aim for improving TB treatment is to shorten the period of antibiotic therapy without increasing relapse rates or encouraging the development of antibiotic-resistant strains. In any M. tuberculosis population there is a proportion of bacteria that are drug-tolerant; this might be because of pre-existing populations of slow growing/non replicating bacteria that are protected from antibiotic action due to the expression of a phenotype that limits drug activity. We addressed this question by observing populations of either slow growing (constant 69.3h mean generation time) or fast growing bacilli (constant 23.1h mean generation time) in their response to the effects of isoniazid exposure, using controlled and defined growth in chemostats. Phenotypic differences were detected between the populations at the two growth rates including expression of efflux mechanisms and the involvement of antisense RNA/small RNA in the regulation of a drug-tolerant phenotype, which has not been explored previously for M. tuberculosis. Genotypic analyses showed that slow growing bacilli develop resistance to isoniazid through mutations specifically in katG codon Ser315 which are present in approximately 50-90% of all isoniazid-resistant clinical isolates. The fast growing bacilli persisted as a mixed population with katG mutations distributed throughout the gene. Mutations in katG codon Ser315 appear to have a fitness cost in vitro and particularly in fast growing cultures. Our results suggest a requirement for functional katG-encoded catalase-peroxide in the slow growers but not the fast-growing bacteria, which may explain why katG codon Ser315 mutations are favoured in the slow growing cultures.
authors.affiliation: Public Health England, Porton Down, Salisbury, United Kingdom.
authors.forename: Rose E
authors.initials: RE
authors.lastname: Jeeves
authors.affiliation: Public Health England, Porton Down, Salisbury, United Kingdom.
authors.forename: Alice A N
authors.initials: AA
authors.lastname: Marriott
authors.affiliation: Public Health England, Porton Down, Salisbury, United Kingdom.
authors.forename: Steven T
authors.initials: ST
authors.lastname: Pullan
authors.affiliation: Public Health England, Porton Down, Salisbury, United Kingdom.
authors.forename: Kim A
authors.initials: KA
authors.lastname: Hatch
authors.affiliation: Public Health England, Porton Down, Salisbury, United Kingdom.
authors.forename: Jon C
authors.initials: JC
authors.lastname: Allnutt
authors.affiliation: Public Health England, Porton Down, Salisbury, United Kingdom.
authors.forename: Irene
authors.initials: I
authors.lastname: Freire-Martin
authors.affiliation: Public Health England, Porton Down, Salisbury, United Kingdom.
authors.forename: Charlotte L
authors.initials: CL
authors.lastname: Hendon-Dunn
authors.affiliation: Public Health England, Porton Down, Salisbury, United Kingdom.
authors.forename: Robert
authors.initials: R
authors.lastname: Watson
authors.affiliation: St George's, University of London, Cranmer Terrace, London, United Kingdom.
authors.forename: Adam A
authors.initials: AA
authors.lastname: Witney
authors.affiliation: St George's, University of London, Cranmer Terrace, London, United Kingdom.
authors.forename: Richard H
authors.initials: RH
authors.lastname: Tyler
authors.affiliation: Public Health England, Colindale, 61 Colindale Avenue, London, United Kingdom.
authors.forename: Catherine
authors.initials: C
authors.lastname: Arnold
authors.affiliation: Public Health England, Porton Down, Salisbury, United Kingdom.
authors.forename: Philip D
authors.initials: PD
authors.lastname: Marsh
authors.affiliation: University College London, Centre for Clinical Microbiology, Royal Free Campus, Rowland Hill Street, London, United Kingdom.
authors.forename: Timothy D
authors.initials: TD
authors.lastname: McHugh
authors.affiliation: Public Health England, Porton Down, Salisbury, United Kingdom.
authors.forename: Joanna
authors.initials: J
authors.lastname: Bacon
mesh_terms: D000995:Antitubercular Agents / Q000494:pharmacology / Q000627:therapeutic use*; D001426:Bacterial Proteins / Q000235:genetics*; D002374:Catalase / Q000235:genetics*; D003062:Codon; D004252:DNA Mutational Analysis; D004352:Drug Resistance, Microbial / Q000235:genetics*; D020869:Gene Expression Profiling; D015964:Gene Expression Regulation, Bacterial / Q000187:drug effects; D015971:Gene Expression Regulation, Enzymologic / Q000187:drug effects; D006801:Humans; D007538:Isoniazid / Q000494:pharmacology / Q000627:therapeutic use*; D008826:Microbial Sensitivity Tests; D009169:Mycobacterium tuberculosis / Q000187:drug effects / Q000235:genetics* / Q000254:growth & development*; D017354:Point Mutation; D020641:Polymorphism, Single Nucleotide; D012694:Serine / Q000235:genetics; D018088:Tuberculosis, Multidrug-Resistant / Q000235:genetics / Q000382:microbiology
chemical_list: D000995:Antitubercular Agents; D001426:Bacterial Proteins; D003062:Codon; D012694:Serine; D002374:Catalase; C480353:katG protein, Mycobacterium tuberculosis; D007538:Isoniazid