Targeting bedaquiline mycobacterial efflux pump to potentially enhance therapy in Mycobacterium abscessus.

Background: Mycobacterium abscessus is notorious for being intrinsically resistant to most antibiotics. Antibiotic efflux is one of the mechanisms used by M. abscessus to pump out antibiotics from their cells. Inhibiting efflux pumps (EPs) can be an attractive strategy to enhance the activity of drugs. The objective of this study is to determine the activity of EP inhibitors (EPIs) to enhance the efficacy of the new drug bedaquiline against M. abscessus clinical isolates. Methods: A total of 31 phenotypically and genotypically identified M. abscessus subsp. abscessus, M. abscesss subsp. massiliense, and M. abscessus subsp. bolletii clinical isolates were studied. The contribution of EPs was determined by investigating the minimum inhibitory concentration (MIC) levels of bedaquiline reduction in the absence and presence of EPIs verapamil and reserpine using the resazurin microtiter assay. Results: The observed bedaquiline MIC reduction by verapamil was observed in 100% isolates and by reserpine in 54.8% isolates. Bedaquiline MIC was 4-32-fold using verapamil with M. abscessus subsp. bolletii showing the highest fold change and between 2- and 4-fold using reserpine. Conclusions: The results obtained in this study confirm that bedaquiline MIC decreased in the presence of EPIs verapamil and reserpine in clinical isolates of M. abscessus. Verapamil was the most effective EPI. As shown in previous studies, verapamil may have clinical potential as adjunctive therapy to enhance the effect of bedaquiline.

Laboratory diagnosis of nontuberculous mycobacteria in a Belgium Hospital.

Background: Nontuberculous mycobacteria (NTM) have been identified in human pulmonary and extrapulmonary infections and are increasing globally, which makes it challenging to identify them. This article reports our experience with the laboratory identification of NTM in clinical practice among pulmonary and extrapulmonary samples received in our routine work. Methods: The study was conducted at the Université Catholique de Louvain at the Cliniques Universitaires Saint-Luc, Brussels, Belgium, from 2015 to 2018. A total of 386 clinical samples were collected from patients suspected of having pulmonary or extrapulmonary mycobacterial infections. Routine laboratory methods phenotypic and molecular tests were performed. Results: The majority of NTM species were isolated from pulmonary samples (68%). The most prevalent species identified were Mycobacterium chimaera_intracellulare group (32%), followed by Mycobacterium avium complex (21%), Mycobacterium abscessus complex (18%), Mycobacterium gordonae (9%), and Mycobacterium chelonae (4%). In extrapulmonary samples, M. avium and M. chimaera_intracellulare were the most frequently isolated. Conclusion: The species diversity of NTM found in our setting suggests the importance of the use of new modern methods for accurate identification of NTM at species level and in some case at subspecies level for the proper treatment and management of patients.

Comparison of the RGM medium and the mycobacterial growth indicator tube automated system for isolation of non-tuberculous mycobacteria from sputum samples of cystic fibrosis patients in Belgium.

PURPOSE: Pulmonary infections due to non-tuberculous mycobacteria (NTM) are an emerging issue in the cystic fibrosis (CF) population. Due to bacterial and fungal overgrowth, isolation of mycobacteria from the sputum samples of these patients remains challenging. RGM medium, a novel agar-based culture medium was evaluated for the isolation of NTM from sputum samples of CF patients. METHODOLOGY: Sputum samples were inoculated onto RGM medium and conventional Mycobacterial Growth Indicator Tube (MGIT™, Becton Dickinson, USA). Agar plates were incubated at 35 °C and growth was recorded once a week during 42 days. We compared the yield of the two media. RESULTS: 217 samples were obtained from 124 CF patients. 20 samples (13 patients) had a positive culture for NTM. 79/217 (36.4%) MGIT had to be discontinued due to contamination compared to 18/217 (8.3%) for RGM. We reported equivalent NTM detection performances for RGM and MGIT (P = 0.579): these media enabled the isolation of 15 and 12 NTM strains respectively. CONCLUSION: RGM medium increases the proportion of interpretable results and the number of NTM cultured. Taking into account the non-inferiority compared to conventional methods and ease of use of RGM medium, we estimate that this test can replace current approaches for the screening of NTM among people with CF. Additionally, RGM provides semi-quantitative results (number of colonies) and information on the morphology of colonies, which may be clinically relevant information.