Showing papers by "Diana Machado published in 2012"

Contribution of Efflux to the Emergence of Isoniazid and Multidrug Resistance in Mycobacterium tuberculosis

Abstract: Multidrug resistant (MDR) tuberculosis is caused by Mycobacterium tuberculosis resistant to isoniazid and rifampicin, the two most effective drugs used in tuberculosis therapy. Here, we investigated the mechanism by which resistance towards isoniazid develops and how overexpression of efflux pumps favors accumulation of mutations in isoniazid targets, thus establishing a MDR phenotype. The study was based on the in vitro induction of an isoniazid resistant phenotype by prolonged serial exposure of M. tuberculosis strains to the critical concentration of isoniazid employed for determination of drug susceptibility testing in clinical isolates. Results show that susceptible and rifampicin monoresistant strains exposed to this concentration become resistant to isoniazid after three weeks; and that resistance observed for the majority of these strains could be reduced by means of efflux pumps inhibitors. RT-qPCR assessment of efflux pump genes expression showed overexpression of all tested genes. Enhanced real-time efflux of ethidium bromide, a common efflux pump substrate, was also observed, showing a clear relation between overexpression of the genes and increased efflux pump function. Further exposure to isoniazid resulted in the selection and stabilization of spontaneous mutations and deletions in the katG gene along with sustained increased efflux activity. Together, results demonstrate the relevance of efflux pumps as one of the factors of isoniazid resistance in M. tuberculosis. These results support the hypothesis that activity of efflux pumps allows the maintenance of an isoniazid resistant population in a sub-optimally treated patient from which isoniazid genetically resistant mutants emerge. Therefore, the use of inhibitors of efflux should be considered in the development of new therapeutic strategies for preventing the emergence of MDR-TB during treatment.

Inhibitors of mycobacterial efflux pumps as potential boosters for anti-tubercular drugs

Abstract: Tuberculosis is one of the major causes of infection across the world. The emergence of multi-, extensively- and totally drug-resistant strains of Mycobacterium tuberculosis contributes to the lack of therapeutic options available. The mechanisms associated with this resistance could involve mutations in genes coding for target proteins, decreased permeability, increased efflux and so on. Resistance mediated by efflux systems has become more relevant, since these systems help the bacteria to extrude antibiotics until relevant mutations emerge and become established in the population. Therefore, compounds that inhibit these transport systems are of major importance and have been studied in the last few years. Not only do these compounds act on the bacterial efflux systems but they have also been explored for their dual role as boosters of the macrophage-infected cells. The search for novel compounds or combinations of adjuvant compounds and antibiotics to treat mycobacterial multidrug-resistant infections has become a major goal in the treatment of these diseases.