Evidence of multiple insecticide resistance mechanisms in Anopheles gambiae populations in Bangui, Central African Republic

Number of Anopheles (%) tested by bioassays in seven sites of Bangui, Central African Republic by using WHO test kits for adult mosquitoes. Six insecticides of technical grade were used, including two pyrethroids (deltamethrin and lambda-cyhalothrin), one carbamate (bendiocarb), two organophosphates (fenitrothion and malathion) and one organochlorine (DDT). (XLSX 15 kb

Reproducibility of the ribosomal RNA synthesis ratio in sputum and association with markers of mycobacterium tuberculosis burden

The MIND-IHOP study was funded by the IHOP grant (NIH R01 HL090335), Lung MicroCHIP grant (NIH U01 HL098964), and K24 grant (NIH K24 HL087713). These sources provided the funding to support participant enrollment and specimen collection. Emmanuel Musisi was supported by a scholarship from the Pulmonary Complications of AIDS Research Training Program (NIH D43 TW009607). N.D.W., R.M.S., J.L.D., and P.N. acknowledge funding from the U.S. National Institutes of Health (1R01AI127300-01A1). N.D.W. and M.I.V. acknowledge funding from the U.S. National Institutes of Health (1R21AI135652-01). N.D.W. acknowledges funding from Veterans Affairs (1IK2CX000914-01A1 and 1I01BX004527-01A1) and from the Doris Duke Charitable Foundation Clinical Scientist Development Award.There is a critical need for improved pharmacodynamic markers for use in human tuberculosis (TB) drug trials. Pharmacodynamic monitoring in TB has conventionally used culture or molecular methods to enumerate the burden of Mycobacterium tuberculosis organisms in sputum. A recently proposed assay called the rRNA synthesis (RS) ratio measures a fundamentally novel property, how drugs impact ongoing bacterial rRNA synthesis. Here, we evaluated RS ratio as a potential pharmacodynamic monitoring tool by testing pretreatment sputa from 38 Ugandan adults with drug-susceptible pulmonary TB. We quantified the RS ratio in paired pretreatment sputa and evaluated the relationship between the RS ratio and microbiologic and molecular markers of M. tuberculosis burden. We found that the RS ratio was highly repeatable and reproducible in sputum samples. The RS ratio was independent of M. tuberculosis burden, confirming that it measures a distinct new property. In contrast, markers of M. tuberculosis burden were strongly associated with each other. These results indicate that the RS ratio is repeatable and reproducible and provides a distinct type of information from markers of M. tuberculosis burden. Importance This study takes a major next step toward practical application of a novel pharmacodynamic marker that we believe will have transformative implications for tuberculosis. This article follows our recent report in Nature Communications that an assay called the rRNA synthesis (RS) ratio indicates the treatment-shortening of drugs and regimens. Distinct from traditional measures of bacterial burden, the RS ratio measures a fundamentally novel property, how drugs impact ongoing bacterial rRNA synthesis.Publisher PDFPeer reviewe

Evidence of multiple insecticide resistance mechanisms in Anopheles gambiae populations in Bangui, Central African Republic

International audienceBackground: Knowledge of insecticide resistance status in the main malaria vectors is an essential component of effective malaria vector control. This study presents the first evaluation of the status of insecticide resistance in Anopheles gambiae populations from Bangui, the Central African Republic.Methods: Anopheles mosquitoes were reared from larvae collected in seven districts of Bangui between September to November 2014. The World Health Organisation’s bioassay susceptibility tests to lambda-cyhalothrin (0.05%), deltamethrin (0.05%), DDT (4%), malathion (5%), fenitrothion (1%) and bendiocarb (0.1%) were performed on adult females. Species and molecular forms as well as the presence of L1014F kdr and Ace-1R mutations were assessed by PCR. Additional tests were conducted to assess metabolic resistance status.Results: After 1 h exposure, a significant difference of knockdown effect was observed between districts in all insecticides tested except deltamethrin and malathion. The mortality rate (MR) of pyrethroids group ranging from 27% (CI: 19–37.5) in Petevo to 86% (CI: 77.6–92.1) in Gbanikola; while for DDT, MR ranged from 5% (CI: 1.6–11.3) in Centre-ville to 39% (CI: 29.4–49.3) in Ouango. For the organophosphate group a MR of 100% was observed in all districts except Gbanikola where a MR of 96% (CI: 90–98.9) was recorded. The mortality induced by bendiocarb was very heterogeneous, ranging from 75% (CI: 62.8–82.8) in Yapele to 99% (CI: 84.5–100) in Centre-ville. A high levelof kdr-w (L1014F) frequency was observed in all districts ranging from 93 to 100%; however, no kdr-e (L1014S) and Ace-1R mutation were found in all tested mosquitoes. Data of biochemical analysis showed significant overexpression activities of cytochrome P450, GST and esterases in Gbanikola and Yapele (χ2 = 31.85, df = 2, P < 0.001). By contrast, esterases activities using α and β-naphthyl acetate were significantly low in mosquitoes from PK10 and Ouango in comparison to Kisumu strain (χ2 = 17.34, df = 2, P < 0.005).Conclusions: Evidence of resistance to DDT and pyrethroids as well as precocious emergence of resistance to carbamates were detected among A. gambiae mosquitoes from Bangui, including target-site mutations and metabolic mechanisms. The co-existence of these resistance mechanisms in A. gambiae may be a serious obstacle for the future success of malaria control programmes in this region

MOVER approximated CV: A tool for quantifying precision in ratiometric droplet digital PCR assays.

Droplet digital PCR is a particularly valuable tool for ratiometric assays because it provides simultaneous absolute quantification of two target sequences in a single assay. This manuscript addresses a challenge in establishing a new ratiometric droplet digital PCR assay for use in sputum, the rRNA synthesis ratio. In principle, the methods established to evaluate precision and determine the limit of quantification for a single measurand cannot be applied to a ratiometric assay. The precision of a ratio depends on precision in both the numerator and denominator. Here, we evaluated the MOVER approximated coefficient of variation as indicator of assay precision that does not require technical replicates. We estimated the MOVER approximated coefficient of variation in dilution series and routine assays and evaluated its agreement with the traditional coefficient of variation. We found that the MOVER approximated coefficient of variation was able to recapitulate the traditional coefficient of variation without the requirement for replicate assays. We also demonstrated that the MOVER approximated coefficient of variation threshold can be used to define the limit of quantification of the rRNA synthesis Ratio. In conclusion, the MOVER approximated coefficient of variation may be useful not only for the rRNA synthesis ratio but for other assays that measure ratios via droplet digital PCR

Does discovery of differentially culturable M tuberculosis really demand a new treatment paradigm? Longitudinal analysis of DNA clearance from sputum.

BackgroundAccording to the traditional tuberculosis (TB) treatment paradigm, the initial doses of treatment rapidly kill most Mycobacterium tuberculosis (Mtb) bacilli in sputum, yet many more months of daily treatment are required to eliminate a small, residual subpopulation of drug-tolerant bacilli. This paradigm has recently been challenged following the discovery that up to 90% of Mtb bacilli in sputum are culturable only with growth-factor supplementation. These "differentially culturable" bacilli are hypothesized to be more drug-tolerant than routinely culturable bacilli. This hypothesis implies an alternative paradigm in which TB treatment does not rapidly reduce the total Mtb population but only the small, routinely culturable subpopulation. To evaluate these competing paradigms, we developed a culture-independent method for quantifying the viable fraction of Mtb bacilli in sputum during treatment.MethodsWe used GeneXpert MTB/RIF to quantify Mtb DNA in sputa collected longitudinally from Ugandan adults taking standard 4-drug treatment for drug-susceptible pulmonary TB. We modeled GeneXpert cycle thresholds over time using nonlinear mixed-effects regression. We adjusted these models for clearance of DNA from killed-but-not-yet-degraded bacilli, assuming clearance half-lives ranging from 0 to 1.25&nbsp;days. We used a convolution integral to quantify DNA from viable bacilli only, and converted cycle thresholds to Mtb genomic equivalents. We replicated our results in a South African cohort.ResultsWe enrolled 41&nbsp;TB patients in Uganda. Assuming a DNA-clearance half-life of 0&nbsp;days, genomic equivalents of viable sputum bacilli decreased by 0.22 log/day until 8.8&nbsp;days, then by 0.07 log/day afterwards. Assuming a DNA-clearance half-life of 1.25&nbsp;days, genomic equivalents of viable bacilli decreased by 0.36 log/day until 5.0&nbsp;days, then by 0.06 log/day afterwards. By day 7, viable Mtb had decreased by 97.2-98.8%. We found similar results for 19&nbsp;TB patients in South Africa.DiscussionUsing a culture-independent method, we found that TB treatment rapidly eliminates most viable Mtb in sputum. These findings are incompatible with the hypothesis that differentially culturable bacilli are drug-tolerant.ConclusionsA culture-independent method for measuring viable Mtb in sputum during treatment corroborates the traditional TB treatment paradigm in which a rapid bactericidal phase precedes slow, elimination of a small, residual bacillary subpopulation