Suchergebnisse

In a recent report of a systematic review of critical concentrations (CCs), the World Health Organization (WHO) lowered the rifampin (RIF) CC for antimicrobial susceptibility testing (AST) of the Mycobacterium tuberculosis complex using Middlebrook 7H10 medium and the Bactec Mycobacterial Growth Indicator Tube (MGIT) 960 system from 1 to 0.5 μg/ml. The previous RIF CC for 7H10 had been in use for over half a century. Because it had served as the de facto reference standard, it contributed to the endorsement of inappropriately high CCs for other AST methods, including the U.S. Food and Drug Administration (FDA)-approved MGIT system. Moreover, this resulted in confusion about the interpretation of seven borderline resistance mutations in rpoB (i.e., L430P, D435Y, H445L, H445N, H445S, L452P, and I491F). In this issue of the Journal of Clinical Microbiology, Shea et al. (J Clin Microbiol 59:e01885-20, 2021, https://doi.org/10.1128/JCM.01885-20) provide evidence that the CC endorsed by the Clinical and Laboratory Standards Institute for the Sensititre MYCOTB system, which is not FDA approved but is CE-IVD marked in the European Union, is likely also too high. These findings underscore the importance of calibrating AST methods against a rigorously defined reference standard, as recently proposed by the European Committee on Antimicrobial Susceptibility Testing, as well as the value of routine next-generation sequencing for investigating discordant AST results.

In this study, using the Hain GenoType MTBDRsl assays (versions 1 and 2), we found that some nonsynonymous and synonymous mutations in gyrA in Mycobacterium tuberculosis result in systematic false-resistance results to fluoroquinolones by preventing the binding of wild-type probes. Moreover, such mutations can prevent the binding of mutant probes designed for the identification of specific resistance mutations. Although these mutations are likely rare globally, they occur in approximately 7% of multidrug-resistant tuberculosis strains in some settings. ; Funding Agencies|Swedish Heart and Lung Foundation; Marianne and Marcus Wallenberg Foundation; Wellcome Trust [201344/Z/16/Z]; NIHR Oxford Biomedical Research Centre; NIHR Oxford Health Protection Research Unit on Healthcare Associated Infection and Antimicrobial Resistance [HPRU-2012-10041]; Health Innovation Challenge Fund [T5-358, HICF-T5-342, WT098600]; German Center for Infection Research (DZIF); European Union TB-PAN-NET [FP7-223681]; PathoNgenTrace [278864]; UK Department of Health; Pacific Biosciences, Inc.; Illumina, Inc.; Colciencias; Hain Lifescience

A screening of more than 1,500 drug-resistant strains of Mycobacterium tuberculosis revealed evolutionary patterns characteristic of positive selection for three alanine racemase (Alr) mutations. We investigated these mutations using molecular modeling, in vitro MIC testing, as well as direct measurements of enzymatic activity, which demonstrated that these mutations likely confer resistance to D-cycloserine. ; Funding Agencies|University of Otago; Health Research Council; Maurice Wilkins Centre; European Union [FP7-278864-2]; German Center for Infection Research (DZIF); Fundacao para a Ciencia e a Tecnologia, Portugal [UID/Multi/04413/2013, SFRH/BPD/100688/2014, SFRH/BPD/95406/2013]; Wellcome Trust [201344/Z/16/Z]; Medical Research Council UK [MR/K000551/1, MR/M01360X/1, MR/N010469/1]; Indian Council of Medical Research, New Delhi; L2 Diagnostics LLC, New Haven; Pacific Biosciences, Inc.; Illumina, Inc.; European Society of Mycobacteriology; Hain Lifescience; UK Department of Health [HICF-T5-342, WT098600]; Wellcome Trust