Diels, M. | Search bioRxiv

bioRxiv2024

Direct thin-layer agar for bedaquiline-susceptibility testing of Mycobacterium tuberculosis at BSL2 level yields high accuracy in 15 days from sputum processing.

This study evaluated thin-layer agar (TLA) as a faster alternative for both indirect MIC determination of bedaquiline (BDQ) from culture isolates and direct drug-susceptibility testing (DST) from sputum samples. Indirect BDQ-MIC results from TLA were compared to the established 7H11 solid DST. Direct-TLA-DST performance was assessed using 143 baseline sputum samples from rifampicin-resistant TB cases. Direct-TLA tested susceptibility to rifampicin, isoniazid, levofloxacin, and BDQ, with results compared to Lowenstein-Jensen (LJ) and MGIT. For indirect BDQ-MIC determination, TLA demonstrated high accuracy, with MIC values for H37Rv falling within the WHO control range (0.015-0.12g/ml). The incubation conditions (5-10% CO2, standard) and reading time (day 7, 14) significantly affected results, with D7 readings in standard incubator providing optimal accuracy. Direct-TLA-DST detected MTB in 53.8% of samples, compared to 55.9% on LJ and 69.4% in MGIT. Uninterpretable results due to contamination or medium drying were low (4.9%). Median time to result was 15 days for smear-positive and 22 days for smear-negative samples, faster than WHO endorsed methods. Sensitivity was 100% for rifampicin and 87.8% for isoniazid, with a specificity of 100% for all drugs except isoniazid (96.2%). No BDQ nor levofloxacin resistance was detected, thus direct TLA sensitivity could not be assessed. In conclusion, direct-TLA-DST offers a reliable and faster alternative to conventional DST methods for BDQ and other anti-TB drugs. Essentially, this technique can be operated at BioSafety Level 2, allowing decentralization of pDST for managing drug-resistant TB in settings with limited laboratory infrastructure. ImportanceThis paper addresses the critical need for faster direct drug-susceptibility testing (DST) on sputum, especially for bedaquiline (BDQ), which is a key drug in treating drug-resistant TB. Currently, there is a lack of rapid, reliable methods for direct BDQ testing from sputum samples, limiting timely and accurate treatment decisions and monitoring. By demonstrating the potential of thin-layer agar (TLA) for direct BDQ-MIC determination, this study offers a promising solution that could significantly improve patient care.

microbiology↗

bioRxiv2020

A sister lineage of the Mycobacterium tuberculosis complex discovered in the African Great Lakes region

The human- and animal-adapted lineages of the Mycobacterium tuberculosis complex (MTBC) are thought to have clonally expanded from a common progenitor in Africa. However, the molecular events that accompanied this emergence remain largely unknown. Here, we describe two MTBC strains isolated from patients with multidrug-resistant tuberculosis, representing an as-yet-unknown lineage, named Lineage 8 (L8), seemingly restricted to the African Great Lakes region. Using genome-based phylogenetic reconstruction, we show that L8 is a sister clade to the known MTBC lineages. Comparison with other complete mycobacterial genomes indicate that the divergence of L8 preceded the loss of the cobF genome region - involved in the cobalamin/vitamin B12 synthesis - and gene interruptions in a subsequent common ancestor shared by all other known MTBC lineages. This discovery further supports an East African origin for the MTBC and provides additional molecular clues on the ancestral genome reduction associated with adaptation to a pathogenic lifestyle.

microbiology↗