Antimicrobial and Efflux Inhibitor Activity of Usnic Acid Against Mycobacterium abscessus.

New drugs are needed to treat infections with antimicrobial-resistant Mycobacterium abscessus; therefore, we evaluated usnic acid as an antimicrobial agent and efflux inhibitor (EI) against M. abscessus. Usnic acid showed antimicrobial activity, and synergistically, the EI verapamil increased this activity. In addition, when we evaluated the interaction of antimicrobials with usnic acid, the increase of their activity was observed. Finally, usnic acid showed an efflux inhibitory effect between the classical EIs verapamil and carbonyl cyanide m-chlorophenylhydrazine. In conclusion, usnic acid showed both antimicrobial and EI activity, indicating that this natural compound may be a promising scaffold for new drugs against this difficult-to-treat microorganism.

Tetrahydropyridine derivative as efflux inhibitor in Mycobacterium abscessus.

OBJECTIVES: This study aimed to evaluate a tetrahydropyridine derivative (THP) as a potential inhibitor of the efflux mechanism and modulator of the high level of antimicrobial resistance usually observed in members of the Mycobacterium abscessus (M. abscessus) group. METHODS: The strain M. abscessus subsp. abscessus (ATCC 19997) was used as reference, in addition to three clinical isolates: M. abscessus subsp. abscessus (AT 07), and two M. abscessus subsp. bolletii (AT 46 and AT 52). The minimum inhibitory concentration (MIC) of amikacin (AMI), ciprofloxacin (CIP), clarithromycin (CLA), verapamil (VP), and THP derivative (NUNL02) was determined. RESULTS: The NUNL02 showed activity against M. abscessus; the MIC of AMI against ATCC 19997 was reduced more than 16-fold, and the MIC of CIP against AT 52 was reduced four-fold. When combined with CLA, the MIC was reduced against all tested strains. In addition, to detect and quantify the activity of the efflux mechanism, the intracellular accumulation kinetics of the fluorometric substrate ethidium bromide in the presence and absence of VP and NUNL02 were evaluated. The NUNL02 was found to be a more effective efflux inhibitor than VP, which is the classical inhibitor. CONCLUSIONS: The tetrahydropyridine derivative, NUNL02, is a promising adjuvant in the treatment of infections caused by M. abscessus.

In silico and in vitro evaluation of tetrahydropyridine compounds as efflux inhibitors in Mycobacterium abscessus.

Herein, we evaluated tetrahydropyridine (THP) compounds (NUNM) as antimicrobials and inhibitors of the efflux mechanism in M. abscessus. subsp. abscessus. The modulation factor (MF) of efflux inhibitors was calculated from the minimum inhibitory concentrations (MICs) of amikacin (AMI), ciprofloxacin (CIP) and clarithromycin (CLA) in the absence and presence of subinhibitory concentrations of the NUNM compounds and canonical inhibitors carbonyl cyanide m-chlorophenyl hydrazone (CCCP) and verapamil (VP). The kinetics of the intracellular accumulation of the fluorimetric substrate ethidium bromide (EtBr) was evaluated and calculated by the relative final fluorescence (RFF). In addition, molecular modeling simulations for the MmpL5 and Tap efflux transporters with ligands (CLA, NUNM, CCCP, VP and EtBr) were performed to better understand the efflux mechanism. We highlight the NUNM01 compound because it reduced the MICs of AMI, CIP and CLA by 4-, 4- and 16-fold, respectively, had the highest effect on EtBr accumulation (RFF = 3.1) and showed a significant in silico affinity for the evaluated proteins in docking simulations. Based on the analyses performed in vitro and in silico, we propose that NUNM01 is a potential pharmacophore candidate for the development of a therapeutic adjuvant for M. abscessus infections.

The Contribution of Efflux Pumps in Mycobacterium abscessus Complex Resistance to Clarithromycin.

The basis of drug resistance in Mycobacterium abscessus is still poorly understood. Nevertheless, as seen in other microorganisms, the efflux of antimicrobials may also play a role in M. abscessus drug resistance. Here, we investigated the role of efflux pumps in clarithromycin resistance using nine clinical isolates of M. abscessus complex belonging to the T28 erm(41) sequevar responsible for the inducible resistance to clarithromycin. The strains were characterized by drug susceptibility testing in the presence/absence of the efflux inhibitor verapamil and by genetic analysis of drug-resistance-associated genes. Efflux activity was quantified by real-time fluorometry. Efflux pump gene expression was studied by RT-qPCR upon exposure to clarithromycin. Verapamil increased the susceptibility to clarithromycin from 4- to ≥64-fold. The efflux pump genes MAB_3142 and MAB_1409 were found consistently overexpressed. The results obtained demonstrate that the T28 erm(41) polymorphism is not the sole cause of the inducible clarithromycin resistance in M. abscessus subsp. abscessus or bolletii with efflux activity providing a strong contribution to clarithromycin resistance. These data highlight the need for further studies on M. abscessus efflux response to antimicrobial stress in order to implement more effective therapeutic regimens and guidance in the development of new drugs against these bacteria.