Activity of rifampicin and linezolid combination in Mycobacterium tuberculosis.

BACKGROUND: Linezolid (LZD) is not commonly used for treating tuberculosis (TB), but in some patients with drug-resistant TB it is being used. However, the in vitro LZD activity, in combination with rifampicin (RIF) against Mycobacterium tuberculosis has not been fully elucidated. AIMS: The aim of this study was to evaluate the in vitro activity of RIF/LZD combination against M. tuberculosis clinical isolates. MATERIALS AND METHODS: The activity of the RIF/LZD combination was firstly determined in M. tuberculosis H37Rv, 14 susceptible, 9 isoniazid nonresistant and 14 multi-drug resistant (MDR) M. tuberculosis clinical isolates by modified checkerboard assay, Resazurin Drugs Combination Microtiter Assay (REDCA). After, the Time Kill Curve Assay, at 0.5 × MIC of drugs, in combination and alone, was performed in M. tuberculosis H37Rv and 8 (20.5%) of those clinical isolates, which the RIF/LZD combination showed to have synergistic effect by the checkerboard assay. RESULTS AND CONCLUSION: By Time Kill Curve Assay, we could observe in M. tuberculosis H37Rv and susceptible isolates, that LZD alone, at sub inhibitory concentration, has poor effect on the bacillus death. In some cases, the bacillus growth stayed constant while in others showed regrowth at the eighth day of drug exposure. RIF alone exhibits potent concentration-dependent bactericidal activity, and was strongly dependent by the drug exposure time. The RIF/LZD combination accomplished a bacteriostatic effect in the reference strain and susceptible isolates. For the RIF resistant isolates, the RIF/LZD combination did not enhance the effect in killing bacillus. In this sense, additional, in vitro and in vivo studies are needed to evaluate the effect of RIF/LZD combination in order to better understand the adjunctive action of LZD in the treatment of TB and prevent the emergence of mutants with resistance to the available anti-TB drugs.

Activity of rifampicin and linezolid combination in Mycobacteriumtuberculosis

Background: Linezolid (LZD) is not commonly used for treating tuberculosis (TB), but in some patients with drug-resistant TB it is being used. However, the in vitro LZD activity, in combination with rifampicin (RIF) against Mycobacterium tuberculosis has not been fully elucidated.Aims: The aim of this study was to evaluate the in vitro activity of RIF/LZD combination against M. tuberculosis clinical isolates.Materials and methods: The activity of the RIF/LZD combination was firstly determined in M. tuberculosis H37Rv, 14 susceptible, 9 isoniazid nonresistant and 14 multi-drug resistant (MDR) M. tuberculosis clinical isolates by modified checkerboard assay, Resazurin Drugs Combination Microtiter Assay (REDCA). After, the Time Kill Curve Assay, at 0.5 MIC of drugs, in combination and alone, was performed in M. tuberculosis H37Rv and 8 (20.5%) of those clinical isolates, which the RIF/LZD combination showed to have synergistic effect by the checkerboard assay.Results and conclusion: By Time Kill Curve Assay, we could observe in M. tuberculosis H37Rv and susceptible isolates, that LZD alone, at sub inhibitory concentration, has poor effect on the bacillus death. In some cases, the bacillus growth stayed constant while in others showed regrowth at the eighth day ofdrug exposure. RIF alone exhibits potent concentration-dependent bactericidal activity, and was strongly dependent by the drug exposure time. The RIF/LZD combination accomplished a bacteriostatic effect in the reference strain and susceptible isolates. For the RIF resistant isolates, the RIF/LZD combination did not enhance the effect in killing bacillus. In this sense, additional, in vitro and in vivo studies are needed to evaluate the effect of RIF/LZD combination in order to better understand the adjunctive action of LZD in the treatment of TB and prevent the emergence of mutants with resistance to the available anti-TB drugs.

In vitro activity of rifampicin and verapamil combination in multidrug-resistant mycobacterium tuberculosis.

The aim of the present study was to evaluate the effect of the combination of rifampicin (RIF) and verapamil (VP) against the Mycobacterium tuberculosis H37Rv reference strain and six multidrug-resistant (MDR) M. tuberculosis clinical isolates by determining Time-Kill Curves and the ability to efflux drug by fluorometry. The RIF+VP combination showed synergism in one MDR clinical isolate. For the other five MDR clinical isolates, the drug combination showed no interaction. The MDR clinical isolate had lower ethidium bromide (EtBr) accumulation when exposed to the RIF+VP combination, compared with RIF and VP exposure alone. The other MDR clinical isolates showed no significant difference in EtBr accumulation. These results suggest greater efflux action in one of the MDR clinical isolates compared with the M. tuberculosis H37Rv reference strain. The other five MDR isolates may have additional mechanisms of drug resistance to RIF. The use of the RIF+VP combination made one MDR bacillus more susceptible to RIF probably by inhibiting efflux pumps, and this combination therapy, in some cases, may contribute to a reduction of resistance to RIF in M. tuberculosis.