Resistance to First-Line Anti-TB Drugs Is Associated with Reduced Nitric Oxide Susceptibility in Mycobacterium tuberculosis

Background and objective: The relative contribution of nitric oxide (NO) to the killing of Mycobacterium tuberculosis in human tuberculosis (TB) is controversial, although this has been firmly established in rodents. Studies have demonstrated that clinical strains of M. tuberculosis differ in susceptibility to NO, but how this correlates to drug resistance and clinical outcome is not known. Methods: In this study, 50 sputum smear- and culture-positive patients with pulmonary TB in Gondar, Ethiopia were included. Clinical parameters were recorded and drug susceptibility profile and spoligotyping patterns were investigated. NO susceptibility was studied by exposing the strains to the NO donor DETA/NO. Results: Clinical isolates of M. tuberculosis showed a dose- and time-dependent response when exposed to NO. The most frequent spoligotypes found were CAS1-Delhi and T3_ETH in a total of nine known spoligotypes and four orphan patterns. There was a significant association between reduced susceptibility to NO (>10% survival after exposure to 1mM DETA/NO) and resistance against first-line anti-TB drugs, in particular isoniazid (INH). Patients infected with strains of M. tuberculosis with reduced susceptibility to NO showed no difference in cure rate or other clinical parameters, but a tendency towards lower rate of weight gain after two months of treatment. Conclusion: There is a correlation between resistance to first-line anti-TB drugs and reduced NO susceptibility in clinical strains of M. tuberculosis. Further studies including the mechanisms of reduced NO susceptibility are warranted and could identify targets for new therapeutic interventions

Antioxidants Protect Keratinocytes against M. ulcerans Mycolactone Cytotoxicity

BACKGROUND: Mycobacterium ulcerans is the causative agent of necrotizing skin ulcerations in distinctive geographical areas. M. ulcerans produces a macrolide toxin, mycolactone, which has been identified as an important virulence factor in ulcer formation. Mycolactone is cytotoxic to fibroblasts and adipocytes in vitro and has modulating activity on immune cell functions. The effect of mycolactone on keratinocytes has not been reported previously and the mechanism of mycolactone toxicity is presently unknown. Many other macrolide substances have cytotoxic and immunosuppressive activities and mediate some of their effects via production of reactive oxygen species (ROS). We have studied the effect of mycolactone in vitro on human keratinocytes--key cells in wound healing--and tested the hypothesis that the cytotoxic effect of mycolactone is mediated by ROS. METHODOLOGY/PRINCIPAL FINDINGS: The effect of mycolactone on primary skin keratinocyte growth and cell numbers was investigated in serum free growth medium in the presence of different antioxidants. A concentration and time dependent reduction in keratinocyte cell numbers was observed after exposure to mycolactone. Several different antioxidants inhibited this effect partly. The ROS inhibiting substance deferoxamine, which acts via chelation of Fe(2+), completely prevented mycolactone mediated cytotoxicity. CONCLUSIONS/SIGNIFICANCE: This study demonstrates that mycolactone mediated cytotoxicity can be inhibited by deferoxamine, suggesting a role of iron and ROS in mycolactone induced cytotoxicity of keratinocytes. The data provide a basis for the understanding of Buruli ulcer pathology and the development of improved therapies for this disease

Genomic and functional analyses of mycobacterium tuberculosis strains implicate ald in D-cycloserine resistance.

CAPRISA, 2016.Abstract available in PDF file

Evaluation of the Commercial Kit SIRE Nitratase for detecting resistant Mycobacterium tuberculosis in Brazil

This study was supported by the Minas Gerais State Research Support Foundation (FAPEMIG) protocol number 65/10 and the National Council for Scientific and Technological Development [Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)] protocol number 310174/2014-7-CNPQ.Universidade Federal de Minas Gerais. Faculdade de Medicina. Grupo de Pesquisa em Micobactérias. Belo Horizonte, MG, Brasil.Universidade Federal de Minas Gerais. Faculdade de Medicina Grupo de Pesquisa em Micobactérias. Belo Horizonte, MG, Brasil.Ministério da Saúde. Secretaria de Vigilância em Saúde. Instituto Evandro Chagas. Ananindeua, PA, Brasil.Universidade Federal de Minas Gerais. Faculdade de Medicina Grupo de Pesquisa em Micobactérias. Belo Horizonte, MG, Brasil.Universidade Federal de Minas Gerais. Faculdade de Medicina Grupo de Pesquisa em Micobactérias. Belo Horizonte, MG, Brasil.Universidade Federal do Rio de Janeiro. Programa Acadêmico de Tuberculose. Rio de Janeiro, RJ, Brasil.Universidade Federal de Minas Gerais. Faculdade de Farmácia. Belo Horizonte, MG, Brasil.Universidade Federal de Minas Gerais. Consultoria e Apoio Técnico. Belo Horizonte, MG, Brasil.Introduction: This study aimed to evaluate a new commercial kit, Kit SIRE Nitratase-PlastLabor, for testing the drug susceptibility of clinical Mycobacterium tuberculosis isolates. Methods: The accuracy of the Kit SIRE Nitratase was evaluated by examining the susceptibility (streptomycin, isoniazid, rifampicin, and ethambutol) of 40 M. tuberculosis isolates, using the proportion method with Lowenstein-Jensen medium or the BACTEC MGIT 960 system. Results: The detection accuracy for streptomycin, isoniazid, rifampicin, and ethambutol was 95%, 97.5%, 100%, and 80%, respectively. Conclusions: The exceptional accuracy demonstrated by Kit SIRE Nitratase for isoniazid and rifampicin makes the kit an attractive option for screening M. tuberculosis strain resistance