title: Virulence of Mycobacterium tuberculosis after Acquisition of Isoniazid Resistance: Individual Nature of katG Mutants and the Possible Role of AhpC.
abstract: In the last decade, there were 10 million new tuberculosis cases per year globally. Around 9.5% of these cases were caused by isoniazid resistant (INHr) Mycobacterium tuberculosis (Mtb) strains. Although isoniazid resistance in Mtb is multigenic, mutations in the catalase-peroxidase (katG) gene predominate among the INHr strains. The effect of these drug-resistance-conferring mutations on Mtb fitness and virulence is variable. Here, we assessed differences in bacterial growth, immune response and pathology induced by Mtb strains harboring mutations at the N-terminus of the katG gene. We studied one laboratory and one clinically isolated Mtb clonal pair from different genetic lineages. The INHr strain in each pair had one and two katG mutations with significantly reduced levels of the enzyme and peroxidase activity. Both strains share the V1A mutation, while the double mutant clinical INHr had also the novel E3V katG mutation. Four groups of C57BL/6 mice were infected with one of the Mtb strains previously described. We observed a strong reduction in virulence (reduced bacterial growth), lower induction of proinflammatory cytokines and significantly reduced pathology scores in mice infected with the clinical INHr strain compared to the infection caused by its INHs progenitor strain. On the other hand, there was a subtle reduction of bacteria growth without differences in the pathology scores in mice infected with the laboratory INHr strain. Our results also showed distinct alkyl-hydroperoxidase C (AhpC) levels in the katG mutant strains, which could explain the difference in the virulence profile observed. The difference in the AhpC levels between clonal strains was not related to a genetic defect in the gene or its promoter. Cumulatively, our results indicate that the virulence, pathology and fitness of INHr strains could be negatively affected by multiple mutations in katG, lack of the peroxidase activity and reduced AhpC levels.
authors.affiliation: Department of Microbiology, Immunology and Pathology, Colorado State University, Fort Collins, Colorado, United States of America.
authors.forename: Luisa Maria
authors.initials: LM
authors.lastname: Nieto R
authors.affiliation: Department of Microbiology, Immunology and Pathology, Colorado State University, Fort Collins, Colorado, United States of America.
authors.forename: Carolina
authors.identifier: http://orcid.org/0000-0002-7634-5131
authors.initials: C
authors.lastname: Mehaffy
authors.affiliation: Department of Microbiology, Immunology and Pathology, Colorado State University, Fort Collins, Colorado, United States of America.
authors.forename: Elizabeth
authors.initials: E
authors.lastname: Creissen
authors.affiliation: Department of Microbiology, Immunology and Pathology, Colorado State University, Fort Collins, Colorado, United States of America.
authors.forename: JoLynn
authors.initials: J
authors.lastname: Troudt
authors.affiliation: Department of Microbiology, Immunology and Pathology, Colorado State University, Fort Collins, Colorado, United States of America.
authors.forename: Amber
authors.initials: A
authors.lastname: Troy
authors.affiliation: School of Veterinary Science, University of Queensland, Gatton, Queensland, Australia; Australian Infectious Diseases Research Centre, University of Queensland, St Lucia, Queensland, Australia.|School of Chemistry and Molecular Biosciences, University of Queensland, St Lucia, Queensland, Australia.
authors.forename: Helle
authors.initials: H
authors.lastname: Bielefeldt-Ohmann
authors.affiliation: Division of Infectious Diseases, Department of Medicine, University of New Mexico, Albuquerque, New Mexico, United States of America.
authors.forename: Marcos
authors.initials: M
authors.lastname: Burgos
authors.affiliation: Department of Microbiology, Immunology and Pathology, Colorado State University, Fort Collins, Colorado, United States of America.
authors.forename: Angelo
authors.initials: A
authors.lastname: Izzo
authors.affiliation: Department of Microbiology, Immunology and Pathology, Colorado State University, Fort Collins, Colorado, United States of America.
authors.forename: Karen M
authors.identifier: http://orcid.org/0000-0001-7115-8524
authors.initials: KM
authors.lastname: Dobos
mesh_terms: D000818:Animals; D000995:Antitubercular Agents / Q000494:pharmacology; D001426:Bacterial Proteins / Q000235:genetics* / Q000378:metabolism; D002374:Catalase / Q000235:genetics* / Q000378:metabolism; D016207:Cytokines / Q000378:metabolism; D024881:Drug Resistance, Bacterial / Q000187:drug effects / Q000235:genetics*; D005260:Female; D007538:Isoniazid / Q000494:pharmacology*; D008168:Lung / Q000382:microbiology / Q000473:pathology; D008810:Mice, Inbred C57BL; D009154:Mutation; D009169:Mycobacterium tuberculosis / Q000187:drug effects* / Q000235:genetics / Q000472:pathogenicity*; D010544:Peroxidases / Q000235:genetics / Q000378:metabolism; D014376:Tuberculosis / Q000382:microbiology / Q000473:pathology
chemical_list: D000995:Antitubercular Agents; D001426:Bacterial Proteins; D016207:Cytokines; D010544:Peroxidases; D002374:Catalase; C480353:katG protein, Mycobacterium tuberculosis; D007538:Isoniazid