Implementing best practices on data generation and reporting of Mycobacterium tuberculosis in vitro assays within the ERA4TB consortium.

Tuberculosis (TB) is the historical leading cause of death by a single infectious agent. The European Regimen Accelerator for Tuberculosis (ERA4TB) is a public-private partnership of 30+ institutions with the objective to progress new anti-TB regimens into the clinic. Thus, robust and replicable results across independent laboratories are essential for reliable interpretation of treatment efficacy. A standardization workgroup unified in vitro protocols and data reporting templates. Time-kill assays provide essential input data for pharmacometric model-informed translation of single agents and regimens activity from in vitro to in vivo and the clinic. Five conditions were assessed by time-kill assays in six independent laboratories using four bacterial plating methods. Baseline bacterial burden varied between laboratories but variability was limited in net drug effect, confirming 2.5 µL equally robust as 100 µL plating. This exercise establishes the foundations of collaborative data generation, reporting, and integration within the overarching Antimicrobial Resistance Accelerator program.

In vitro activity of bedaquiline against slow-growing nontuberculous mycobacteria.

Bedaquiline (BDQ) is a recently approved antibiotic for the treatment of multidrug-resistant tuberculosis, but its potential against slow-growing mycobacteria (SGM) is still unknown. The objective of this study was to determine the in vitro activity of BDQ on SGM by assessing their MIC and minimal bactericidal concentration (MBC). The MIC of BDQ against 17 clinical isolates including Mycobacterium avium, Mycobacterium intracellulare, Mycobacterium chimaera, Mycobacterium kansasii and Mycobacterium simiae species was determined by the resazurin microtitre assay and the MBC by the c.f.u. determination on 7H10 agar plates. BDQ has a bacteriostatic activity on all SGM tested with a MIC range from 0.03 to 0.007 µg ml-1 and surprisingly a good bactericidal activity on the majority of the isolates tested with an MBC of 1-2 µg ml-1 . Based on these preliminary results BDQ seems to be very promising for treatment of diseases caused by SGM.

Antimicrobial activity against Mycobacterium tuberculosis under in vitro lipid-rich dormancy conditions.

Although tuberculosis treatment is dependent on drug-susceptibility testing (DST) and molecular drug-resistance detection, treatment failure and relapse remain a challenge. This could be partially due to the emergence of antibiotic-tolerant dormant mycobacteria, where host lipids have been shown to play an important role. This study evaluated the susceptibility of Mycobacterium tuberculosis to two antibiotic combinations - rifampicin, moxifloxacin, amikacin and metronidazole (RIF-MXF-AMK-MTZ), and rifampicin, moxifloxacin, amikacin and pretomanid (RIF-MXF-AMK-PA) - in a lipid-rich dormancy model. Although their effectiveness in in vitro cultures with dextrose as a carbon source has been proved, we observed that none of the antibiotic mixtures were bactericidal in the presence of lipids. The presence of lipids may confer tolerance to M. tuberculosis against the mixture of antibiotics tested and such tolerance could be even higher during the dormant stages. The implementation of lipids in DST on clinical isolates could potentially lead to a better treatment strategy.