Biology subjects

Tabor, S. T.

Publications and source records attributed to Tabor, S. T..

3 recordsLinked to original sources

bioRxiv2025

Same class, different activity: Delamanid and pretomanid have comparable bactericidal activity but pretomanid potently inhibits Mycobacterium tuberculosis ribosomal rRNA synthesis

BackgroundThe nitroimidazoles delamanid and pretomanid play an important role in contemporary tuberculosis treatment. It is unclear whether delamanid and pretomanid have meaningfully different activity since both reduce Mycobacterium tuberculosis colony forming units (CFU) similarly in animal models. The RS ratio is a pharmacodynamic marker of ongoing rRNA synthesis that has been associated with treatment-shortening (i.e., sterilizing) activity. MethodsUsing Mycobacterium tuberculosis Erdman, we conducted dose-ranging studies in aerobic axenic culture and in the conventional BALB/c mouse high-dose aerosol infection model to compare bactericidal and RS ratio activity of delamanid and pretomanid. ResultsIn vitro concentration-response curves showed that delamanid and pretomanid had similar RS ratio effect at maximal concentration but pretomanid was more potent, achieving 90% of the maximal effect (RS-EC90) at a lower concentration (390 ng/mL) than delamanid (810 ng/mL). In mice, delamanid and pretomanid had similar effects on CFU. Human-equivalent doses of delamanid (6 mg/kg) and pretomanid (50 mg/kg) resulted in plasma Cmax concentrations well below (210 ng/mL) and well above (7,825 ng/mL) the RS-EC90, respectively. Delamanid displayed no discernable RS ratio response, even at 16-times the human-equivalent dose. Higher pretomanid doses resulted in significantly greater RS ratio effects. ConclusionsWe found that delamanid and pretomanid have similar bactericidal activity but pretomanid has superior RS ratio activity. Meaningful differences between drugs within the same class were not captured by conventional CFU-based pharmacodynamics, supporting the value of measuring orthogonal drug effects such as the RS ratio. LAY SUMMARYAntibiotics in the nitroimidazole class are used in treatment of drug-resistant tuberculosis. There are two approved nitroimidazole antibiotics: delamanid and pretomanid. For decades, it has been unclear whether delamanid and pretomanid are interchangeable or whether they affect the bacterium M. tuberculosis differently. Most studies of the effect of antibiotics count the number of bacterial colonies that form on a culture plate. "Colony forming units" tell us about change in bacterial burden but does not give information about bacterial health. A new way of thinking about antibiotic effect is the RS ratio. The RS ratio is a test that measures how much ribosomal RNA synthesis is ongoing. Ribosomal RNA synthesis is a "vital sign" of bacterial health and activity. The key finding of this study is that although the two nitroimdazole antibiotics look the same in terms of their effect on bacterial burden, they have different effects on bacterial health. This information deepens understanding of differences between two clinically important antibiotics. It also shows that antibiotics testing should consider not only bacterial burden but also new tests of bacterial health.

microbiology↗

bioRxiv2025

Mind the gap: Understanding discordance between culture- and a non-culture-based measure of bacterial burden in murine tuberculosis treatment models

The standard pharmacodynamic marker in murine tuberculosis drug studies is colony-forming units (CFU). A faster PCR-based marker of bacterial burden is 16S rRNA. For unclear reasons, treatment reduces CFU more than 16S rRNA. We evaluated this CFU-16S gap and estimated the fraction potentially attributable to slow decay of 16S rRNA from dead Mycobacterium tuberculosis (Mtb) versus transition to a viable but not culturable on solid agar (VBNCSA) population. We quantified the CFU-16S gap during and following treatment in six BALB/c mouse studies and one in vitro study. Applying a two-population ordinary differential equation-based model of Mtb death and 16S rRNA decay, we estimated the fraction of the gap potentially attributable to dead Mtb. Using meta-regression, we estimated the association between CFU or 16S rRNA with relapse. For all regimens, CFU fell more than 16S rRNA, ranging from isoniazid-rifampin-pyrazinamide-ethambutol (CFU decreased 39-times more than 16S rRNA at week 4) to bedaquiline-pretomanid-moxifloxacin-pyrazinamide (CFU decreased >500,000-times more). The two-population model suggested that the fraction of the CFU-16S gap attributable to residual 16S rRNA from dead Mtb is modest and decreases over time. After treatment, 16S rRNA often fell while CFU rose. Four-week CFU change explained most variation in relapse (R{superscript 2}=0.90) while four-week 16S rRNA change did not (R{superscript 2}=0.24). CFU-16S gap is only partially explained by slow decay of residual 16S, suggesting development of a VBNCSA population. However, continued decrease in 16S rRNA after treatment cessation and its limited association with relapse suggests VBNCSA may be a transient rather than persistent state.

microbiology↗

bioRxiv2023

Transcriptional adaptation of drug-tolerant Mycobacterium tuberculosis in mice

Transcriptome evaluation of Mycobacterium tuberculosis in the lungs of laboratory animals during long-term treatment has been limited by extremely low abundance of bacterial mRNA relative to eukaryotic RNA. Here we report a targeted amplification RNA sequencing method called SEARCH-TB. After confirming that SEARCH-TB recapitulates conventional RNA-seq in vitro, we applied SEARCH-TB to Mycobacterium tuberculosis-infected BALB/c mice treated for up to 28 days with the global standard isoniazid, rifampin, pyrazinamide, and ethambutol regimen. We compared results in mice with 8-day exposure to the same regimen in vitro. After treatment of mice for 28 days, SEARCH-TB suggested broad suppression of genes associated with bacterial growth, transcription, translation, synthesis of rRNA proteins and immunogenic secretory peptides. Adaptation of drug-stressed Mycobacterium tuberculosis appeared to include a metabolic transition from ATP-maximizing respiration towards lower-efficiency pathways, modification and recycling of cell wall components, large-scale regulatory reprogramming, and reconfiguration of efflux pumps expression. Despite markedly different expression at pre-treatment baseline, murine and in vitro samples had broadly similar transcriptional change during treatment. The differences observed likely indicate the importance of immunity and pharmacokinetics in the mouse. By elucidating the long-term effect of tuberculosis treatment on bacterial cellular processes in vivo, SEARCH-TB represents a highly granular pharmacodynamic monitoring tool with potential to enhance evaluation of new regimens and thereby accelerate progress towards a new generation of more effective tuberculosis treatment.

microbiology↗