Ethambutol and meropenem/clavulanate synergy promotes enhanced extracellular and intracellular killing of Mycobacterium tuberculosis

Increasing evidence supports the repositioning of beta-lactams for tuberculosis (TB) therapy, but further research on their interaction with conventional anti-TB agents is still warranted. Moreover, the complex cell envelope of Mycobacterium tuberculosis (Mtb) may pose an additional obstacle to beta-lactam diffusion. In this context, we aimed to identify synergies between beta-lactams and anti-TB drugs ethambutol (EMB) and isoniazid (INH) by assessing antimicrobial effects, intracellular activity, and immune responses. Checkerboard assays with H37Rv and eight clinical isolates, including four drug-resistant strains, exposed that only treatments containing EMB and beta-lactams achieved synergistic effects. Meanwhile, the standard EMB and INH association failed to produce any synergy. In Mtb-infected THP-1 macrophages, combinations of EMB with increasing meropenem (MEM) concentrations consistently displayed superior killing activities over the individual antibiotics. Flow cytometry with BODIPY FL vancomycin, which binds directly to the peptidoglycan (PG), confirmed an increased exposure of this layer after co-treatment. This was reinforced by the high IL-1β secretion levels found in infected macrophages after incubation with MEM concentrations above 5 mg/L, indicating an exposure of the host innate response sensors to pathogen-associated molecular patterns in the PG. Our findings show that the proposed impaired access of beta-lactams to periplasmic transpeptidases is counteracted by concomitant administration with EMB. The efficiency of this combination may be attributed to the synchronized inhibition of arabinogalactan and PG synthesis, two key cell wall components. Given that beta-lactams exhibit a time-dependent bactericidal activity, a more effective pathogen recognition and killing prompted by this association may be highly beneficial to optimize TB regimens containing carbapenems.IMPORTANCEAddressing drug-resistant tuberculosis with existing therapies is challenging and the treatment success rate is lower when compared to drug-susceptible infection. This study demonstrates that pairing beta-lactams with ethambutol (EMB) significantly improves their efficacy against Mycobacterium tuberculosis (Mtb). The presence of EMB enhances beta-lactam access through the cell wall, which may translate into a prolonged contact between the drug and its targets at a concentration that effectively kills the pathogen. Importantly, we showed that the effects of the EMB and meropenem (MEM)/clavulanate combination were maintained intracellularly. These results are of high significance considering that the time above the minimum inhibitory concentration is the main determinant of beta-lactam efficacy. Moreover, a correlation was established between incubation with higher MEM concentrations during macrophage infection and increased IL-1β secretion. This finding unveils a previously overlooked aspect of carbapenem repurposing against tuberculosis, as certain Mtb strains suppress the secretion of this key pro-inflammatory cytokine to evade host surveillance.

Bigger problems from smaller colonies: emergence of antibiotic-tolerant small colony variants of Mycobacterium avium complex in MAC-pulmonary disease patients

BACKGROUND

Mycobacterium avium complex (MAC) is a group of slow-growing mycobacteria that includes Mycobacterium avium and Mycobacterium intracellulare. MAC pulmonary disease (MAC-PD) poses a threat to immunocompromised individuals and those with structural pulmonary diseases worldwide. The standard treatment regimen for MAC-PD includes a macrolide in combination with rifampicin and ethambutol. However, the treatment failure and disease recurrence rates after successful treatment remain high.

RESULTS

In the present study, we investigated the unique characteristics of small colony variants (SCVs) isolated from patients with MAC-PD. Furthermore, revertant (RVT) phenotype, emerged from the SCVs after prolonged incubation on 7H10 agar. We observed that SCVs exhibited slower growth rates than wild-type (WT) strains but had higher minimum inhibitory concentrations (MICs) against multiple antibiotics. However, some antibiotics showed low MICs for the WT, SCVs, and RVT phenotypes. Additionally, the genotypes were identical among SCVs, WT, and RVT. Based on the MIC data, we conducted time-kill kinetic experiments using various antibiotic combinations. The response to antibiotics varied among the phenotypes, with RVT being the most susceptible, WT showing intermediate susceptibility, and SCVs displaying the lowest susceptibility.

CONCLUSIONS

In conclusion, the emergence of the SCVs phenotype represents a survival strategy adopted by MAC to adapt to hostile environments and persist during infection within the host. Additionally, combining the current drugs in the treatment regimen with additional drugs that promote the conversion of SCVs to RVT may offer a promising strategy to improve the clinical outcomes of patients with refractory MAC-PD.

Clofazimine as a substitute for rifampicin improves efficacy of Mycobacterium avium pulmonary disease treatment in the hollow-fiber model

Mycobacterium avium complex pulmonary disease is treated with an azithromycin, ethambutol, and rifampicin regimen, with limited efficacy. The role of rifampicin is controversial due to inactivity, adverse effects, and drug interactions. Here, we evaluated the efficacy of clofazimine as a substitute for rifampicin in an intracellular hollow-fiber infection model. THP-1 cells, which are monocytes isolated from peripheral blood from an acute monocytic leukemia patient, were infected with M. avium ATCC 700898 and exposed to a regimen of azithromycin and ethambutol with either rifampicin or clofazimine. Intrapulmonary pharmacokinetic profiles of azithromycin, ethambutol, and rifampicin were simulated. For clofazimine, a steady-state average concentration was targeted. Drug concentrations and bacterial densities were monitored over 21 days. Exposures to azithromycin and ethambutol were 20%-40% lower than targeted but within clinically observed ranges. Clofazimine exposures were 1.7 times higher than targeted. Until day 7, both regimens were able to maintain stasis. Thereafter, regrowth was observed for the rifampicin-containing regimen, while the clofazimine-containing regimen yielded a 2 Log10 colony forming unit (CFU) per mL decrease in bacterial load. The clofazimine regimen also successfully suppressed the emergence of macrolide tolerance. In summary, substitution of rifampicin with clofazimine in the hollow-fiber model improved the antimycobacterial activity of the regimen. Clofazimine-containing regimens merit investigation in clinical trials.

Ethambutol inhibited the growth of acid-fast bacteria and enhanced the detection of Legionella in environmental water samples

The growth of acid-fast bacteria often hinders the detection of Legionella in water samples on agar plates by the plate culture method. We studied whether anti-tubercular agents inhibit acid-fast bacteria growth on agar plates. First, the antimicrobial activities of isoniazid, ethionamide, and ethambutol were evaluated against Mycobacterium and Legionella. We found that ethambutol at ≥ 100 μg/mL completely inhibited Mycobacterium growth, but ethambutol at 1,000 μg/mL did not inhibit Legionella growth. Next, the effect of ethambutol dissolved in acid buffer was examined. Cell suspensions of L. pneumophila and Mycobacterium spp. were mixed, and ethambutol-acid buffer was added. After 5 min, mixtures were inoculated on GVPC agar plates and incubated at 36℃ for 6 d. We found that ethambutol inhibited Mycobacterium growth on agar plates, but the Legionella colonies recovered. The effect of ethambutol was also significant in the evaluation using bathwaters. Comparing 1,302 bathwaters, the addition of ethambutol reduced the detection rate of acid-fast bacteria from 30.6% to 0% and increased the detection rate of Legionella from 7.1% to 7.5%. Ethambutol, which selectively inhibited acid-fast bacteria growth, enhanced the detection of Legionella on agar plates and will contribute to improving the accuracy of Legionella testing by the plate culture method.

Protein binding investigation of first-line and second-line antituberculosis drugs

Data on protein binding are incomplete for first-line antituberculosis drugs, and lacking for second-line antituberculosis drugs that are used extensively for multi-drug-resistant tuberculosis (levofloxacin, linezolid and moxifloxacin). Thus, the main purposes of this study were to investigate: (i) the relationship between carrier protein concentration and drug binding; and (ii) the feasibility of predicting free drug concentration using in-vitro and in-vivo results. In-vitro experiments were performed on spiked plasma mimicking real-case samples (drug combinations from clinical practice). Median in-vivo protein binding was 1.5% for ethambutol, 9.7% for isoniazid, 0.7% for pyrazinamide and 88.2% for rifampicin; and median in-vitro protein binding was 26.2% for levofloxacin, 12.8% for linezolid and 46.3% for moxifloxacin. Albumin concentration (<30 g/L) had a moderate impact on moxifloxacin binding and a strong impact on levofloxacin, linezolid and rifampicin binding. Determination of the free drug concentration seems to be of little value for ethambutol, isoniazid, moxifloxacin and pyrazinamide; limited value for linezolid because of its low binding; and major value for rifampicin in hypoalbuminaemic patients with tuberculosis, and levofloxacin because total concentration was an inaccurate reflection of free concentration. The free concentration predicted by the mathematical model was suitable for levofloxacin and linezolid, whereas the real free concentration should be measured for rifampicin. Further investigations should be carried out to investigate the benefit of using free concentration for levofloxacin, linezolid and rifampicin, particularly in the critical period of active tuberculosis associated with hypoalbuminaemia.

Evaluating the Sensitivity of Different Molecular Techniques for Detecting Mycobacterium tuberculosis Complex in Patients with Pulmonary Infection

This study aimed to evaluate the accuracy of detecting drug-resistant Mycobacterium tuberculosis complex (MTBC)-specific DNA in sputum specimens from 48 patients diagnosed with pulmonary tuberculosis. The presence of MTBC DNA in the specimens was validated using the GeneXpert MTB/RIF system and compared with a specific PCR assay targeting the IS6110 and the mtp40 gene sequence fragments. Additionally, the results obtained by multiplex PCR assays to detect the most frequently encountered rifampin, isoniazid, and ethambutol resistance-conferring mutations were matched with those obtained by GeneXpert and phenotypic culture-based drug susceptibility tests. Of the 48 sputum samples, 25 were positive for MTBC using the GeneXpert MTB/RIF test. Nevertheless, the IS6110 and mtp40 single-step PCR revealed the IS6110 in 27 of the 48 sputum samples, while the mtp40 gene fragment was found in only 17 of them. Furthermore, multiplex PCR assays detected drug-resistant conferring mutations in 21 (77.8%) of the 27 samples with confirmed MTBC DNA, 10 of which contained single drug-resistant conferring mutations towards ethambutol and two towards rifampin, and the remaining nine contained double-resistant mutations for ethambutol and rifampin. In contrast, only five sputum specimens (18.5%) contained drug-resistant MTBC isolates, and two contained mono-drug-resistant MTBC species toward ethambutol and rifampin, respectively, and the remaining three were designated as multi-drug resistant toward both drugs using GeneXpert and phenotypic culture-based drug susceptibility tests. Such discrepancies in the results emphasize the need to develop novel molecular tests that associate with phenotypic non-DNA-based assays to improve the detection of drug-resistant isolates in clinical specimens in future studies.

The role of rifampicin within the treatment of Mycobacterium avium pulmonary disease

Rifampicin is recommended for the treatment of Mycobacterium avium complex pulmonary disease alongside azithromycin and ethambutol. We evaluated the azithromycin-ethambutol backbone with and without rifampicin in an intracellular hollow fiber model and performed RNA sequencing to study the differences in adaptation. In an in vitro hollow fiber experiment, we simulated epithelial lining fluid pharmacokinetic profiles of the recommended 3-drug (rifampicin, ethambutol, and azithromycin) or a 2-drug (ethambutol and azithromycin) treatment. THP-1 cells infected with M. avium ATCC700898 were exposed to these regimens for 21 days. We determined intra- and extra-cellular bacterial load- and THP-1 cell densities on days 0, 3, 7, 14, and 21, alongside RNA sequencing. The emergence of macrolide resistance was studied by inoculating intra- and extra-cellular fractions of azithromycin-containing Middlebrook 7H10 agar plates. Complete pharmacokinetic profiles were determined at days 0 and 21. Both therapies maintained stasis of both intra- and extra-cellular bacterial populations for 3 days, whilst regrowth coinciding with the emergence of a macrolide-resistant subpopulation was seen after 7 days. THP-1 cell density remained static. Similar transcriptional profiles were observed for both therapies that were minimally influenced by exposure duration. Transcriptional response was slightly larger during 2-drug treatment. Rifampicin did not add to the antimycobacterial effect to the 2-drug therapy or suppression of emergence resistance. RNA transcription was not greatly altered by the addition of rifampicin, which may be due to strong transcriptional influence of azithromycin and host cells. This questions the role of rifampicin in the currently recommended therapy. These findings should be confirmed in clinical trials.

Evaluation of two colorimetric microplate microtiter tests for susceptibility testing of clinical isolates of Mycobacterium tuberculosis to first-line antituberculosis drugs

Background

Drug-resistance tuberculosis (TB) is one of the most important global public health problems. Accurate and rapid drug-susceptibility testing is critical for the effective treatment of TB patients. Various colorimetric methods are used for anti-TB drug-susceptibility testing (DST) and minimum inhibitory concentration (MIC) determination. This study was conducted to evaluate the resazurin microtiter assay (REMA) and malachite green decolorization assay (MGDA).

Methods

A total of 65 Mycobacterium tuberculosis strains isolated from patients with suspected TB using REMA and malachite green microtiter assay methods were tested against streptomycin (SM), isoniazid (INH), rifampicin (RIF), and ethambutol (ETB). The Mycobacterial Growth Indicator Tube 960 DST method was accepted as the gold standard in the evaluation of test results.

Results

The sensitivity of REMA and MGDA tests was found to be 87.5% and 62.5% for INH, respectively. RIF and SM sensitivity for both tests was 100%. While ETB sensitivity was 81.8 for the REMA test, this rate was 60% for the MGDA test. Specificity of both tests varied between 92.5% and 98.2% according to the drug types.

Conclusion

REMA and MGDA are a simple, rapid, and low cost. They can be used as an alternative test for drug-susceptibility testing and MIC determination. Extensive studies and standardization are needed for the routine use of both tests.

The potential role of drug transporters and amikacin modifying enzymes in M. avium

OBJECTIVES

Mycobacterium avium (M. avium) complex bacteria cause opportunistic infections in humans. Treatment yields cure rates of 60% and consists of a macrolide, a rifamycin, and ethambutol, and in severe cases, amikacin. Mechanisms of antibiotic tolerance remain mostly unknown. Therefore, we studied the contribution of efflux and amikacin modification to antibiotic susceptibility.

METHODS

We characterised M. avium ABC transporters and studied their expression together with other transporters following exposure to clarithromycin, amikacin, ethambutol, and rifampicin. We determined the effect of combining the efflux pump inhibitors berberine, verapamil and CCCP (carbonyl cyanide m-chlorophenyl hydrazone), to study the role of efflux on susceptibility. Finally, we studied the modification of amikacin by M. avium using metabolomic analysis.

RESULTS

Clustering shows conservation between M. avium and M. tuberculosis and transporters from most bacterial subfamilies (2-6, 7a/b, 10-12) were found. The largest number of transporter encoding genes was up-regulated after clarithromycin exposure, and the least following amikacin exposure. Only berberine increased the susceptibility to clarithromycin. Finally, because of the limited effect of amikacin on transporter expression, we studied amikacin modification and showed that M. avium, in contrast to M. abscessus, is not able to modify amikacin.

CONCLUSION

We show that M. avium carries ABC transporters from all major families important for antibiotic efflux, including homologues shown to have affinity for drugs included in treatment. Efflux inhibition in M. avium can increase susceptibility, but this effect is efflux pump inhibitor- and antibiotic-specific. Finally, the lack of amikacin modifying activity in M. avium is important for its activity.

Wollamide Cyclic Hexapeptides Synergize with Established and New Tuberculosis Antibiotics in Targeting Mycobacterium tuberculosis

Shorter and more effective treatment regimens as well as new drugs are urgent priorities for reducing the immense global burden of tuberculosis (TB). As treatment of TB currently requires multiple antibiotics with diverse mechanisms of action, any new drug lead requires assessment of potential interactions with existing TB antibiotics. We previously described the discovery of wollamides, a new class of Streptomyces-derived cyclic hexapeptides with antimycobacterial activity. To further assess the value of the wollamide pharmacophore as an antimycobacterial lead, we determined wollamide interactions with first- and second-line TB antibiotics by determining fractional inhibitory combination index and zero interaction potency scores. In vitro two-way and multiway interaction analyses revealed that wollamide B1 synergizes with ethambutol, pretomanid, delamanid, and para-aminosalicylic acid in inhibiting the replication and promoting the killing of phylogenetically diverse clinical and reference strains of the Mycobacterium tuberculosis complex (MTBC). Wollamide B1 antimycobacterial activity was not compromised in multi- and extensively drug-resistant MTBC strains. Moreover, growth-inhibitory antimycobacterial activity of the combination of bedaquiline/pretomanid/linezolid was further enhanced by wollamide B1, and wollamide B1 did not compromise the antimycobacterial activity of the isoniazid/rifampicin/ethambutol combination. Collectively, these findings add new dimensions to the desirable characteristics of the wollamide pharmacophore as an antimycobacterial lead compound. IMPORTANCE Tuberculosis (TB) is an infectious disease that affects millions of people globally, with 1.6 million deaths annually. TB treatment requires combinations of multiple different antibiotics for many months, and toxic side effects can occur. Therefore, shorter, safer, more effective TB therapies are required, and these should ideally also be effective against drug-resistant strains of the bacteria that cause TB. This study shows that wollamide B1, a chemically optimized member of a new class of antibacterial compounds, inhibits the growth of drug-sensitive as well as multidrug-resistant Mycobacterium tuberculosis isolated from TB patients. In combination with TB antibiotics, wollamide B1 synergistically enhances the activity of several antibiotics, including complex drug combinations that are currently used for TB treatment. These new insights expand the catalogue of the desirable characteristics of wollamide B1 as an antimycobacterial lead compound that might inspire the development of improved TB treatments.

The efficient induction of human retinal ganglion-like cells provides a platform for studying optic neuropathies

Retinal ganglion cells (RGCs) are essential for vision perception. In glaucoma and other optic neuropathies, RGCs and their optic axons undergo degenerative change and cell death; this can result in irreversible vision loss. Here we developed a rapid protocol for directly inducing RGC differentiation from human induced pluripotent stem cells (hiPSCs) by the overexpression of ATOH7, BRN3B, and SOX4. The hiPSC-derived RGC-like cells (iRGCs) show robust expression of various RGC-specific markers by whole transcriptome profiling. A functional assessment was also carried out and this demonstrated that these iRGCs display stimulus-induced neuronal activity, as well as spontaneous neuronal activity. Ethambutol (EMB), an effective first-line anti-tuberculosis agent, is known to cause serious visual impairment and irreversible vision loss due to the RGC degeneration in a significant number of treated patients. Using our iRGCs, EMB was found to induce significant dose-dependent and time-dependent increases in cell death and neurite degeneration. Western blot analysis revealed that the expression levels of p62 and LC3-II were upregulated, and further investigations revealed that EMB caused a blockade of lysosome-autophagosome fusion; this indicates that impairment of autophagic flux is one of the adverse effects of that EMB has on iRGCs. In addition, EMB was found to elevate intracellular reactive oxygen species (ROS) levels increasing apoptotic cell death. This could be partially rescued by the co-treatment with the ROS scavenger NAC. Taken together, our findings suggest that this iRGC model, which achieves both high yield and high purity, is suitable for investigating optic neuropathies, as well as being useful when searching for potential drugs for therapeutic treatment and/or disease prevention.

Isoniazid pharmacokinetics/pharmacodynamics as monotherapy and in combination regimen in the hollow fiber system model of Mycobacterium kansasii

BACKGROUND

There is limited high quality evidence to guide the optimal doses of drugs for the treatment of Mycobacterium kansasii pulmonary disease (Mkn-PD).

METHODS

We performed (1) minimum inhibitory concentration experiment, (2) isoniazid dose-response study using the hollow fiber system model (HFS-Mkn) to determine PK/PD optimized exposure, and (3) another HFS-Mkn study to determine the efficacy of high dose isoniazid (15 mg/kg/day) with standard dose rifampin (10 mg/kg/day) and ethambutol (15 mg/kg/day). Inhibitory sigmoid maximal effect model and linear regression was used for data analysis.

RESULTS

MIC of the 20 clinical isolates ranged between 0.5 mg/L to 32 mg/L. In the HFS-Mkn, isoniazid monotherapy failed to control the bacterial growth beyond day 7. On day 7, when the maximal Mkn kill was observed, the optimal isoniazid exposure for Mkn kill was calculated as 24hr area under the concentration-time curve to the MIC of 12.41. Target attainment probability of 300 mg/day dose fell below 90% above the MIC of 1 mg/L. High dose isoniazid combination sterilized the HFS-Mkn in 30-days with a kill rate of -0.15 ± 0.02 log10 CFU/mL/day.

CONCLUSION

Despite initial kill, isoniazid monotherapy failed due to resistance emergence. Our pre-clinical model derived results suggest that higher than currently recommended 300 mg/day isoniazid dose may achieve better clinical efficacy against Mkn-PD.

Evaluation Study of xMAP TIER Assay on a Microsphere-Based Platform for Detecting First-Line Anti-Tuberculosis Drug Resistance

Early diagnosis of drug susceptibility for tuberculosis (TB) patients could guide the timely initiation of effective treatment. We evaluated a novel multiplex xMAP TIER (Tuberculosis-Isoniazid-Ethambutol-Rifampicin) assay based on the Luminex xMAP system to detect first-line anti-tuberculous drug resistance. Deoxyribonucleic acid samples from 353 Mycobacterium tuberculosis clinical isolates were amplified by multiplex polymerase chain reaction, followed by hybridization and analysis through the xMAP system. Compared with the broth microdilution method, the sensitivity and specificity of the xMAP TIER assay for detecting resistance was 94.9% (95%CI, 90.0-99.8%) and 98.9% (95%CI, 97.7-100.0%) for rifampicin; 89.1% (95%CI, 83.9-94.3%) and 100.0% (95%CI, 100.0-100.0%) for isoniazid; 82.1% (95% CI, 68.0-96.3%) and 99.7% (95% CI, 99.0-100.0%) for ethambutol. With DNA sequencing as the reference standard, the sensitivity and specificity of xMAP TIER for detecting resistance were 95.0% (95% CI, 90.2-99.8%) and 99.6% (95% CI, 98.9-100.0%) for rifampicin; 96.9% (95% CI, 93.8-99.9%) and 100.0% (95% CI, 100.0-100.0%) for isoniazid; 86.1% (95% CI, 74.8-97.4%) and 100.0% (95% CI, 100.0-100.0%) for ethambutol. The results achieved showed that the xMAP TIER assay had good performance for detecting first-line anti-tuberculosis drug resistance, and it has the potential to diagnose drug-resistant tuberculosis more accurately due to the addition of more optimal design primers and probes on open architecture xMAP system.

An efficient CRISPR interference-based prediction method for synergistic/additive effects of novel combinations of anti-tuberculosis drugs

Tuberculosis (TB) is treated by chemotherapy with multiple anti-TB drugs for a long period, spanning 6 months even in a standard course. In perspective, to prevent the emergence of antimicrobial resistance, novel drugs that act synergistically or additively in combination with major anti-TB drugs and, if possible, shorten the duration of TB therapy are needed. However, their combinatorial effect cannot be predicted until the lead identification phase of the drug development. Clustered regularly interspaced short palindromic repeats interference (CRISPRi) is a powerful genetic tool that enables high-throughput screening of novel drug targets. The development of anti-TB drugs promises to be accelerated by CRISPRi. This study determined whether CRISPRi could be applicable for predictive screening of the combinatorial effect between major anti-TB drugs and an inhibitor of a novel target. In the checkerboard assay, isoniazid killed Mycobacterium smegmatis synergistically or additively in combinations with rifampicin or ethambutol, respectively. The susceptibility to rifampicin and ethambutol was increased by knockdown of inhA, which encodes a target molecule of isoniazid. Additionally, knockdown of rpoB, which encodes a target molecule of rifampicin, increased the susceptibility to isoniazid and ethambutol, which act synergistically with rifampicin in the checkerboard assay. Moreover, CRISPRi could successfully predict the synergistic action of cyclomarin A, a novel TB drug candidate, with isoniazid or rifampicin. These results demonstrate that CRISPRi is a useful tool not only for drug target exploration but also for screening the combinatorial effects of novel combinations of anti-TB drugs. This study provides a rationale for anti-TB drug development using CRISPRi.

Integration of network pharmacology and intestinal flora to investigate the mechanism of action of Chinese herbal Cichorium intybus formula in attenuating adenine and ethambutol hydrochloride-induced hyperuricemic nephropathy in rats

CONTEXT

Cichorium intybus L. (Asteraceae) formula (CF) has been applied as a folk medicine to treat hyperuricemic nephropathy (HN). However, the exact mechanism remains unclear.

OBJECTIVE

To explore the therapeutic effect and mechanism of CF on HN.

MATERIALS AND METHODS

Through network pharmacological methods, the targets of the active component of CF against HN were obtained. Subsequently, Male Wistar rats were divided into control, HN, allopurinol (50 mg/kg), CF high-dose (8.64 g/kg) and CF low-dose (2.16 g/kg) groups. The HN model was induced via intragastric administration of adenine (100 mg/kg) and ethambutol hydrochloride (250 mg/kg) for 3 weeks. After CF treatment, biochemical indicators including UA, UREA and CREA were measured. Then, HE staining, qRT-PCR and gut microbiota analysis were conducted to further explore the mechanism.

RESULTS

The network pharmacology identified 83 key targets, 6 core genes and 200 signalling pathways involved in the treatment of HN. Compared to the HN group, CF (8.64 g/kg) significantly reduced the levels of UA, UREA and CREA (from 2.4 to 1.57 μMol/L, from 15.87 to 11.05 mMol/L and from 64.83 to 54.83 μMol/L, respectively), and mitigated renal damage. Furthermore, CF inhibited the expression of IL-6, TP53, TNF and JUN. It also altered the composition of gut microbiota, and ameliorated HN by increasing the relative abundance of some probiotics.

CONCLUSIONS

This work elucidated the therapeutic effect and underlying mechanism by which CF protects against HN from the view of the biodiversity of the intestinal flora, thus providing a scientific basis for the usage of CF.

mbtD and celA1 association with ethambutol resistance in Mycobacterium tuberculosis: A multiomics analysis

Ethambutol (EMB) is a first-line antituberculosis drug currently being used clinically to treat tuberculosis. Mutations in the embCAB operon are responsible for EMB resistance. However, the discrepancies between genotypic and phenotypic EMB resistance have attracted much attention. We induced EMB resistance in Mycobacterium tuberculosis in vitro and used an integrated genome–methylome–transcriptome–proteome approach to study the microevolutionary mechanism of EMB resistance. We identified 509 aberrantly methylated genes (313 hypermethylated genes and 196 hypomethylated genes). Moreover, some hypermethylated and hypomethylated genes were identified using RNA-seq profiling. Correlation analysis revealed that the differential methylation of genes was negatively correlated with transcription levels in EMB-resistant strains. Additionally, two hypermethylated candidate genes (mbtD and celA1) were screened by iTRAQ-based quantitative proteomics analysis, verified by qPCR, and corresponded with DNA methylation differences. This is the first report that identifies EMB resistance-related genes in laboratory-induced mono-EMB-resistant M. tuberculosis using multi-omics profiling. Understanding the epigenetic features associated with EMB resistance may provide new insights into the underlying molecular mechanisms.

Evaluation of the broth microdilution plate methodology for susceptibility testing of Mycobacterium tuberculosis in Peru

BACKGROUND

Tuberculosis (TB) is a communicable, preventable and curable disease caused by the bacterium Mycobacterium tuberculosis (MTB). Peru is amongst the 30 countries with the highest burden of multidrug-resistant tuberculosis (MDR-TB) worldwide. In the fight against drug-resistant tuberculosis, the UKMYC6 microdilution plate was developed and validated by the CRyPTIC project. The objective of the study was to evaluate the use of the broth microdilution (BMD) plate methodology for susceptibility testing of drug-resistant MTB strains in Peru.

METHODS

MTB strains isolated between 2015 and 2018 in Peru were used. 496 nationally-representative strains determined as drug-resistant by the routine 7H10 Agar Proportion Method (APM) were included in the present study. The Minimum Inhibitory Concentration (MIC) of 13 antituberculosis drugs were determined for each strain using the UKMYC6 microdilution plates. Diagnostic agreement between APM and BMD plate methodology was determined for rifampicin, isoniazid, ethambutol, ethionamide, kanamycin and levofloxacin. Phenotypes were set using binary (or ternary) classification based on Epidemiological cut-off values (ECOFF/ECV) proposed by the CRyPTIC project. Whole Genome Sequencing (WGS) was performed on strains with discrepant results between both methods.

RESULTS

MIC distributions were determined for 13 first- and second-line anti-TB drugs, including new (bedaquiline, delamanid) and repurposed (clofazimine, linezolid) agents. MIC results were available for 80% (397/496) of the strains at 14 days and the remainder at 21 days. The comparative analysis determined a good agreement (0.64 ≤ k ≤ 0.79) for the drugs rifampicin, ethambutol, ethionamide and kanamycin, and the best agreement (k > 0.8) for isoniazid and levofloxacin. Overall, 12% of MIC values were above the UKMYC6 plate dilution ranges, most notably for the drugs rifampicin and rifabutin. No strain presented MICs higher than the ECOFF/ECV values for the new or repurposed drugs. Discrepant analysis using genotypic susceptibility testing by WGS supported half of the results obtained by APM (52%, 93/179) and half of those obtained by BMD plate methodology (48%, 86/179).

CONCLUSIONS

The BMD methodology using the UKMYC6 plate allows the complete susceptibility characterization, through the determination of MICs, of drug-resistant MTB strains in Peru. This methodology shows good diagnostic performances for rifampicin, isoniazid, ethambutol, ethionamide, kanamycin and levofloxacin. It also allows for the characterization of MICs for other drugs used in previous years against tuberculosis, as well as for new and repurposed drugs recently introduced worldwide.

Prediction of drug resistance by Sanger sequencing of Mycobacterium tuberculosis complex strains isolated from multidrug resistant tuberculosis suspect patients in Ethiopia

Background

Ethiopia is one of the high multidrug-resistant tuberculosis (MDR-TB) burden countries. However, phenotypic drug susceptibility testing can take several weeks due to the slow growth of Mycobacterium tuberculosis complex (MTBC) strains. In this study, we assessed the performance of a Sanger sequencing approach to predict resistance against five anti-tuberculosis drugs and the pattern of resistance mediating mutations.

Methods

We enrolled 226 MTBC culture-positive MDR-TB suspects and collected sputum specimens and socio-demographic and TB related data from each suspect between June 2015 and December 2016 in Addis Ababa, Ethiopia. Phenotypic drug susceptibility testing (pDST) for rifampicin, isoniazid, pyrazinamide, ethambutol, and streptomycin using BACTEC MGIT 960 was compared with the results of a Sanger sequencing analysis of seven resistance determining regions in the genes rpoB, katG, fabG-inhA, pncA, embB, rpsL, and rrs.

Result

DNA isolation for Sanger sequencing was successfully extracted from 92.5% (209/226) of the MTBC positive cultures, and the remaining 7.5% (17/226) strains were excluded from the final analysis. Based on pDST results, drug resistance proportions were as follows: isoniazid: 109/209 (52.2%), streptomycin: 93/209 (44.5%), rifampicin: 88/209 (42.1%), ethambutol: 74/209 (35.4%), and pyrazinamide: 69/209 (33.0%). Resistance against isoniazid was mainly mediated by the mutation katG S315T (97/209, 46.4%) and resistance against rifampicin by rpoB S531L (58/209, 27.8%). The dominating resistance-conferring mutations for ethambutol, streptomycin, and pyrazinamide affected codon 306 in embB (48/209, 21.1%), codon 88 in rpsL (43/209, 20.6%), and codon 65 in pncA (19/209, 9.1%), respectively. We observed a high agreement between phenotypic and genotypic DST, such as 89.9% (at 95% confidence interval [CI], 84.2%–95.8%) for isoniazid, 95.5% (95% CI, 91.2%–99.8%) for rifampicin, 98.6% (95% CI, 95.9–100%) for ethambutol, 91.3% (95% CI, 84.6–98.1%) for pyrazinamide and 57.0% (95% CI, 46.9%–67.1%) for streptomycin.

Conclusion

We detected canonical mutations implicated in resistance to rifampicin, isoniazid, pyrazinamide, ethambutol, and streptomycin. High agreement with phenotypic DST results for all drugs renders Sanger sequencing promising to be performed as a complementary measure to routine phenotypic DST in Ethiopia. Sanger sequencing directly from sputum may accelerate accurate clinical decision-making in the future.

[Action Mechanism of Ethambutol Tablets on Pulmonary Tuberculosis Rat Model Based on Janus Kinase/Signal Transducer and Activator of Transcription Signaling Pathway]

Objective To explore the therapeutic effect of ethambutol tablets (EMB) on pulmonary tuberculosis (PTB) in rats and whether the action mechanism of EMB is related to Janus kinase (JAK)/signal transducer and activator of transcription (STAT) signaling pathway. Methods Sixty SD rats were assigned into a control group,a PTB group,a PTB+EMB group (30 mg/kg),and a PTB+EMB+Colivelin (JAK/STAT pathway activator) group (30 mg/kg+1 mg/kg) via the random number table method,with 15 rats in each group.The rats in other groups except the control group were injected with 0.2 ml of 5 mg/ml Mycobacterium tuberculosis suspension to establish the PTB model.After the modeling,the rats were administrated with corresponding drugs for 4 consecutive weeks (once a day).On days 1,14,and 28 of administration,the body weights of rats were measured and the Mycobacterium tuberculosis colonies were counted.Hematoxylin-eosin staining was carried out to detect the pathological changes in the lung tissue.Enzyme-linked immunosorbent assay was employed to measure the levels of interleukin(IL)-6,tumor necrosis factor-α (TNF-α),IL-1β,and interferon-γ (IFN-γ) in the serum.Flow cytometry was used to determine the levels of T lymphocyte subsets CD3+,CD4+,CD8+,and CD4+/CD8+.The 16S rRNA sequencing was performed to detect the relative abundance of the intestinal microorganisms.Western blotting was employed to determine the expression of the proteins in the JAK/STAT pathway. Results Compared with the control group,the modeling of PTB reduced the rat body weight (on days 14 and 28),increased Mycobacterium tuberculosis colonies,caused severe pathological changes in the lung tissue,and elevated the levels of IL-6,TNF-α,and IL-1β in serum and CD8+.Moreover,the modeling increased the relative abundance of Bacteroides,Peptococcus,Clostridium,Actinomyces,Lactobacillus,Verrucomicrobium,and Veillonella in the intestine,up-regulated the protein levels of phosphorylated JAK2 and phosphorylated STAT3 in the lung tissue,and lowered the levels of CD3+,CD4+,CD4+/CD8+,and IFN-γ levels (all P<0.001).Compared with the PTB group,PTB+EMB increased the rat body weight (on days 14 and 28),reduced Mycobacterium tuberculosis colonies,alleviated the pathological damage in lung tissue,lowered the levels of IL-6,TNF-α,and IL-1β in serum and CD8+.Moreover,the treatment decreased the relative abundance of Bacteroides,Peptococcus,Clostridium,Actinomyces,Lactobacillus,Verrucomicrobium,Veillonella in the intestine,down-regulated the protein levels of phosphorylated JAK2 and phosphorylated STAT3 in the lung tissue,and elevated the levels of CD3+,CD4+,CD4+/CD8+,and IFN-γ (all P<0.001).Colivelin weakened the alleviation effect of EMB on PTB (all P<0.001). Conclusion EMB can inhibit the JAK/STAT signaling pathway to alleviate the PTB in rat.

Ethambutol-induced bullous skin lesions in mycobacterium kansasii lung infection

Mycobacterium kansasii is the second most common cause of nontuberculous mycobacterial (NTM) lung disease after Mycobacterium avium complex infection in the United States.^[1] The first-line therapy for M. kansasii is a three-drug regimen including rifampin, isoniazid, and ethambutol. We present a case of a patient with pulmonary M. kansasii who developed bullous skin lesions while receiving this regimen and again after rechallenge with ethambutol. In patients with intolerance to one of the first-line antibiotics, a multidisciplinary team approach to starting second-line agents is needed. Ethambutol should be included in the differential diagnosis of drug-induced bullous skin lesions in treated patients with NTM, who develop new onset rash with blisters or ulceration.

Antimycobacterial compound of chitosan and ethambutol: ultrastructural biological evaluation in vitro against Mycobacterium tuberculosis

Chitosan (CS) is a promising biopolymer and has been tested as a complement to the action and compensation of toxicity presented by anti-tuberculosis drugs. The present work studied the adjuvant effect of CS with the drug ethambutol (EMB) as a compound (CS-EMB), to explore its antimicrobial and cytotoxic activity, using transmission electron microscopy (TEM), to examine ultracellular changes that represent possible antimycobacterial action of CS on Mycobacterium tuberculosis (Mtb). Antimycobacterial activities were tested against reference strains Mtb ATCC® H37Rv and multidrug resistant (MDR). In vitro cytotoxicity tests were performed on Raw 264.7. For the studied compounds, morphological, ultrastructural, and physical-chemical analyses were performed. Drug-polymer interactions that occur through the H bridges were confirmed by physical-chemical analyses. The CS-EMB compound is stable at pHs of 6.5-7.5, allowing its release at physiological pH. The antibacterial activity (minimum inhibitory concentration) of the CS-EMB compound was 50% greater than that of the EMB in the H37Rv and MDR strains and the ultrastructural changes in the bacilli observed by TEM proved that the CS-EMB compound has a bactericidal action, allowing it to break down the Mtb cell wall. The cytotoxicity of CS-EMB was higher than that of isolated EMB, IC50 279, and 176 μg/mL, respectively. It is concluded that CS-EMB forms a promising composite against strains Mtb H37Rv and multidrug resistant (MDR-TB).Key points• Our study will be the first to observe ultrastructurally the effects of the CS-EMB compound on Mtb cells.• CS-EMB antimicrobial activity in a multidrug-resistant clinical strain.• The CS-EMB compound has promising potential for the development of a new drug to fight tuberculosis.

Genetic Determinants of Intrinsic Antibiotic Tolerance in Mycobacterium avium

The Mycobacterium avium complex (MAC) is one of the most prevalent causes of nontuberculous mycobacteria pulmonary infection in the United States, and yet it remains understudied. Current MAC treatment requires more than a year of intermittent to daily combination antibiotic therapy, depending on disease severity. In order to shorten and simplify curative regimens, it is important to identify the innate bacterial factors contributing to reduced antibiotic susceptibility, namely, antibiotic tolerance genes. In this study, we performed a genome-wide transposon screen to elucidate M. avium genes that play a role in the bacterium's tolerance to first- and second-line antibiotics. We identified a total of 193 unique M. avium mutants with significantly altered susceptibility to at least one of the four clinically used antibiotics we tested, including two mutants (in DFS55_00905 and DFS55_12730) with panhypersusceptibility. The products of the antibiotic tolerance genes we have identified may represent novel targets for future drug development studies aimed at shortening the duration of therapy for MAC infections. IMPORTANCE The prolonged treatment required to eradicate Mycobacterium avium complex (MAC) infection is likely due to the presence of subpopulations of antibiotic-tolerant bacteria with reduced susceptibility to currently available drugs. However, little is known about the genes and pathways responsible for antibiotic tolerance in MAC. In this study, we performed a forward genetic screen to identify M. avium antibiotic tolerance genes, whose products may represent attractive targets for the development of novel adjunctive drugs capable of shortening the curative treatment for MAC infections.

Distribution and antibiotic sensitivity pattern of Mycobacterium tuberculosis isolates from children, enrolled in a tertiary care hospital

The present study was planned to assess the distribution of tuberculosis in children and evaluate the antimycobacterial sensitivity pattern of Mycobacterium tuberculosis (MTB) isolates from pediatric patients. A total number of 1718 pediatric patients suspected of Mycobacterium tuberculosis were enrolled in the Institute of Child Health and Children's Hospital, Lahore during 2016-17. Out of 1718, only 710 different types of samples were tested for MTB. The samples were processed using bacteriology and GeneXpert along with the chest X-ray and clinical picture of the patients. The sensitivity pattern of Streptomycin, Isoniazid, Rifampicin and Ethambutol (SIRE) was determined using BACTEC MGIT 960. Total patients were divided into four groups including group A (birth to 12 months), B (1 to 5 years), C (6 to 10 years), and D (11 to 15 years). Out of 710, 106 (55 females and 51 males) were declared positive and 604 negative for tuberculosis. Out of 106 positive cases, 89 (83.96%) were sensitive to Rifampicin and 17 (16.04%) were resistant. Only, 04 (3.77%) were resistant to both Rifampicin and Isoniazid and declared as multidrug-resistant (MDR). It was concluded that children of age 11 to 15 years were more prone to MTB and a minimum percentage of MDR isolates was recorded in age group A (birth to 12 months).

Whole-genome sequence analysis and comparisons between drug-resistance mutations and minimum inhibitory concentrations of Mycobacterium tuberculosis isolates causing M/XDR-TB

Drug resistance (DR) remains a major challenge for tuberculosis (TB) control. Whole-genome sequencing (WGS) provides the highest genetic resolution for genotypic drug-susceptibility tests (DST). We compared DST profiles of 60 Mycobacterium tuberculosis isolates which were drug resistant according to agar proportion tests (one poly DR-TB, 34 multidrug-resistant TB and 25 extensively drug-resistant TB). We additionally performed minimum inhibitory concentration (MIC) tests using Sensititre MYCOTBI plates (MYCOTB) and a WGS-based DST. Agreement between WGS-based DST and MYCOTB was high for all drugs except ethambutol (65%) and ethionamide (62%). Isolates harboring the -15 c/t inhA promoter mutation had a significantly lower MIC for isoniazid than did isolates with the katG Ser315Thr mutation (p < 0.001). Similar patterns were seen for ethambutol (embB Gly406Asp vs. embB Met306Ile), streptomycin (gid Gly73Ala vs. rpsL Lys43Arg), moxifloxacin (gyrA Ala90Val vs. gyrA Asp94Gly) and rifabutin (rpoB Asp435Phe/Tyr/Val vs. rpoB Ser450Leu). For genotypic heteroresistance, isolates with lower proportion of mapped read tended to has lower MIC of anti-TB drugs than those with higher proportion. These results emphasize the high applicability of WGS for determination of DR-TB and the association of particular mutations with MIC levels.

Cryo-EM structure of arabinosyltransferase EmbB from Mycobacterium smegmatis

Arabinosyltransferase B (EmbB) belongs to a family of membrane-bound glycosyltransferases that build the lipidated polysaccharides of the mycobacterial cell envelope, and are targets of anti-tuberculosis drug ethambutol. We present the 3.3 Å resolution single-particle cryo-electron microscopy structure of Mycobacterium smegmatis EmbB, providing insights on substrate binding and reaction mechanism. Mutations that confer ethambutol resistance map mostly around the putative active site, suggesting this to be the location of drug binding.

[Clinical characteristics and drug susceptibility test of nontuberculous mycobacterial lung disease]

Objective: To investigate the clinical characteristics and drug susceptibility test (DST) of patients infected with different nontuberculous mycobacteria (NTM). Methods: The patients with nontuberculous mycobacterial lung disease (NMLD) in Shanghai Pulmonary Hospital from March 2014 to March 2015 were studied retrospectively by analyzing the clinical characteristics, radiological features and DST results. A total of 201 NMLD patients [male 108, age(58±15) yrs] were enrolled into this study including 48 cases of M. Kansasii [male 13, age (52±16) yrs],46 cases of M. Abscess[male 46, age (57±16) yrs], 92 cases of M. Intracellulare [male 43, age (61±13) yrs], and 15 cases of M. Avium [male 6, age (67±10) yrs]. Clinical data were collected when the diagnosis was made and Chi-square test was used to compare the differences among 4 groups of patients. Bonferroni method was used for further pairwise comparisons. Results: There were significant differences among the 4 groups in the age(χ(2)=6.42, P<0.001) and the gender(χ(2)=49.18, P<0.001) of the patients. The history of bronchiectasis in the groups of M. Kansasii, M. Abscess, M. Intracellulare and M. Avium were 2/48, 31/46, 39/92 and 4/15 cases respectively(χ(2)=41.84, P<0.001). For the Gamma-interferon release assays (ELISA) (IGRA), the positive rate of IGRA in the groups of M. Kansasii, M. Abscess, M. Intracellulare and M. Avium were 83%(40/48), 30%(14/46), 23%(21/92) and 33% (5/15) respectively(χ(2)=50.96, P<0.001). The radiological features were significantly different in tree-in-bud(8/48, 35/46, 36/92 and 4/15 cases respectively, χ(2)=36.48, P<0.001), pleural thickness or mild effusion (21/48, 36/46, 69/92 and 7/15 cases, χ(2)=19.54, P<0.001), bronchiectasis (20/48, 39/46, 78/92 and 10/15 cases, P<0.001) and cavities (38/48, 21/46, 63/92 and 10/15 cases, χ(2)=12.38, P<0.001) among the 4 groups(M. Kansasii, M. Abscess, M. Intracellulare and M. Avium). The drug resistance rates of M. Kansasii to rifampin, ethambutanol and ofloxacin were 10%(5/48), 8%(4/48) and 15%(7/48) respectively; the resistance rates of M.Intracellulare to ethambutanol was 45%(41/92), and the resistance rates of M.Abscess were all over 80% to all anti-TB drugs. The results of pairwise comparisons showed that the male proportion(46/48) and IGRAs positive rate(40/48) of patients with M. Kansasii were higher than those of other groups, and the incidence of bronchiectasis(20/48) and pleural changes(21/48) was lower than those of other groups. The female ratio(33/46), history of bronchiectasis (31/46) and tree-in-bud sign of patients(35/46) with M. Abscess were higher than those of other groups. Conclusions: There were differences in the clinical manifestations and imaging features of 4 common NMLD diseases, which were helpful for clinical differentiation. The patients with M. Kansasii infection were mainly male, with a high IGRA positive rate and fewer lesions of bronchiectasis or pleural changes. Most of the patients with M. Abscess were female, with a previous history of bronchiectasis, and with most of the lesions showing tree-in-bud signs. The NTM species had a high rate of resistance to anti-TB drugs except M. Kansasii.

Identification of new components of the RipC-FtsEX cell separation pathway of Corynebacterineae

Several important human pathogens are represented in the Corynebacterineae suborder, including Mycobacterium tuberculosis and Corynebacterium diphtheriae. These bacteria are surrounded by a multilayered cell envelope composed of a cytoplasmic membrane, a peptidoglycan (PG) cell wall, a second polysaccharide layer called the arabinogalactan (AG), and finally an outer membrane-like layer made of mycolic acids. Several anti-tuberculosis drugs target the biogenesis of this complex envelope, but their efficacy is declining due to resistance. New therapies are therefore needed to treat diseases caused by these organisms, and a better understanding of the mechanisms of envelope assembly should aid in their discovery. To this end, we generated the first high-density library of transposon insertion mutants in the model organism C. glutamicum. Transposon-sequencing was then used to define its essential gene set and identify loci that, when inactivated, confer hypersensitivity to ethambutol (EMB), a drug that targets AG biogenesis. Among the EMB^s loci were genes encoding RipC and the FtsEX complex, a PG cleaving enzyme required for proper cell division and its predicted regulator, respectively. Inactivation of the conserved steAB genes (cgp_1603–1604) was also found to confer EMB hypersensitivity and cell division defects. A combination of quantitative microscopy, mutational analysis, and interaction studies indicate that SteA and SteB form a complex that localizes to the cytokinetic ring to promote cell separation by RipC-FtsEX and may coordinate its PG remodeling activity with the biogenesis of other envelope layers during cell division.

The pathways involved in bacterial surface assembly are critical for cell morphogenesis and serve as attractive targets for antibiotic development. Bacteria in the suborder Corynebacterineae, which includes important pathogens like Mycobacterium tuberculosis, possess a unique multilayered surface structure. In addition to the common peptidoglycan cell wall, they have an attached polysaccharide layer called arabinogalactan and an outer membrane made of mycolic acids. To enhance our understanding of cell surface biogenesis in these bacteria, we performed a global genetic analysis of gene function in the model system Corynebacterium glutamicum (Cglu) using transposon sequencing. In addition to defining the essential gene set in this organism, our analysis also identified SteA and SteB as components of the cytokinetic ring. These factors are conserved among the Corynebacterineae, and our results reveal that they play a critical role in the final stages of cytokinesis by promoting remodeling of the peptidoglycan layer at the division site.

New insights on Ethambutol Targets in Mycobacterium tuberculosis

BACKGROUND

In recent years, very few effective drugs against Mycobacterium tuberculosis have emerged, which motivates the research with drugs already used in the treatment of tuberculosis. Ethambutol is a bacteriostatic drug that affects cell wall integrity, but the effects of this drug on bacilli are not fully exploited.

OBJECTIVE

Based on the need to better investigate the complex mechanism of action of ethambutol, our study presented the proteome profile of M. tuberculosis after different times of ethambutol exposure, aiming to comprehend the dynamics of bacilli response to its effects. M. tuberculosis was exposed to ½ MIC of ethambutol at 24 and 48 hours. The proteins were identified by MALDI-TOF/TOF.

RESULTS

The main protein changes occurred in metabolic proteins as dihydrolipoyl dehydrogenase (Rv0462), glutamine synthetase1 (Rv2220), electron transfer flavoprotein subunit beta (Rv3029c) and adenosylhomocysteinase (Rv3248c).

CONCLUSION

Considering the functions of these proteins, our results support that the intermediary metabolism and respiration were affected by ethambutol and this disturbance provided proteins that could be explored as additional targets for this drug.

Transformation Morphisms and Time-to-Extinction Analysis That Map Therapy Duration From Preclinical Models to Patients With Tuberculosis: Translating From Apples to Oranges

Background

A major challenge in medicine is translation of preclinical model findings to humans, especially therapy duration. One major example is recent shorter-duration therapy regimen failures in tuberculosis.

Methods

We used set theory mapping to develop a computational/modeling framework to map the time it takes to extinguish the Mycobacterium tuberculosis population on chemotherapy from multiple hollow fiber system model of tuberculosis (HFS-TB) experiments to that observed in patients. The predictive accuracy of the derived translation transformations was then tested using data from 108 HFS-TB Rapid Evaluation of Moxifloxacin in Tuberculosis (REMoxTB) units, including 756 colony-forming units (CFU)/mL. Derived transformations, and Latin hypercube sampling-guided simulations were used to predict cure and relapse after 4 and 6 months of therapy. Outcomes were compared to observations, in 1932 patients in the REMoxTB clinical trial.

Results

HFS-TB serial bacillary burden and serial sputum data in the derivation dataset formed a structure-preserving map. Bactericidal effect was mapped with a single step transformation, while the sterilizing effect was mapped with a 3-step transformation function. Using the HFS-TB REMoxTB data, we accurately predicted the proportion of patients cured in the 4-month REMoxTB clinical trial. Model-predicted vs clinical trial observations were (i) the ethambutol arm (77.0% [95% confidence interval {CI}, 74.4%-79.6%] vs 77.7% [95% CI, 74.3%-80.9%]) and (ii) the isoniazid arm (76.4% [95% CI, 73.9%-79.0%] vs 79.5% [95% CI, 76.1%-82.5%]).

Conclusions

We developed a method to translate duration of therapy outcomes from preclinical models to tuberculosis patients.

Association of ubiA mutations and high-level of ethambutol resistance among Mycobacterium tuberculosis Thai clinical isolates

Ethambutol (EMB) is the first-line antituberculosis drug and a potential supplementary agent for a treatment regimen of multidrug-resistant (MDR) and extensively drug-resistant (XDR) tuberculosis (TB). It has long been known that mutations in embCAB operon, encoding EMB target, arabinosyltransferase, confer resistance to EMB. Recently, ubiA was additionally reported to be specifically associated with high-level EMB resistance in Mycobacterium tuberculosis. However, such information on ubiA is very limited. This study aimed to investigate correlations between mutations in ubiA and phenotypic EMB resistance among EMB-resistant (EMB^R) M. tuberculosis Thai clinical isolates. Minimum inhibitory concentration (MIC) level of EMB and ubiA sequences were determined and analyzed. Of 68 EMB^R-MDR isolates, 8.9% harbored mutations in ubiA. However, 10.0% and 46.6% of EMB-sensitive (EMB^S)-MDR and pan-susceptible isolates also had ubiA mutations detected, respectively. Most nonsynonymous mutations, L31P, A35S, and V55M were only found in the EMB^R-MDR isolates except E149D which was also found in EMB^S-MDR and pan-susceptible isolates. A further phylogenetic analysis based on spoligotyping and IS6110-RFLP illustrated that E149D was in fact associated to EAI-families rather than EMB resistance. By excluding synonymous mutations and the E149D, we found a high correlation between ubiA mutations and high-level of EMB resistance with 100.0% specificity. In conclusion, despite its rare occurrence, mutations in ubiA can potentially be a marker for a detection of high level of EMB resistance at least in the MDR M. tuberculosis background.

Prediction of Susceptibility to First-Line Tuberculosis Drugs by DNA Sequencing

BACKGROUND

The World Health Organization recommends drug-susceptibility testing of Mycobacterium tuberculosis complex for all patients with tuberculosis to guide treatment decisions and improve outcomes. Whether DNA sequencing can be used to accurately predict profiles of susceptibility to first-line antituberculosis drugs has not been clear.

METHODS

We obtained whole-genome sequences and associated phenotypes of resistance or susceptibility to the first-line antituberculosis drugs isoniazid, rifampin, ethambutol, and pyrazinamide for isolates from 16 countries across six continents. For each isolate, mutations associated with drug resistance and drug susceptibility were identified across nine genes, and individual phenotypes were predicted unless mutations of unknown association were also present. To identify how whole-genome sequencing might direct first-line drug therapy, complete susceptibility profiles were predicted. These profiles were predicted to be susceptible to all four drugs (i.e., pansusceptible) if they were predicted to be susceptible to isoniazid and to the other drugs or if they contained mutations of unknown association in genes that affect susceptibility to the other drugs. We simulated the way in which the negative predictive value changed with the prevalence of drug resistance.

RESULTS

A total of 10,209 isolates were analyzed. The largest proportion of phenotypes was predicted for rifampin (9660 [95.4%] of 10,130) and the smallest was predicted for ethambutol (8794 [89.8%] of 9794). Resistance to isoniazid, rifampin, ethambutol, and pyrazinamide was correctly predicted with 97.1%, 97.5%, 94.6%, and 91.3% sensitivity, respectively, and susceptibility to these drugs was correctly predicted with 99.0%, 98.8%, 93.6%, and 96.8% specificity. Of the 7516 isolates with complete phenotypic drug-susceptibility profiles, 5865 (78.0%) had complete genotypic predictions, among which 5250 profiles (89.5%) were correctly predicted. Among the 4037 phenotypic profiles that were predicted to be pansusceptible, 3952 (97.9%) were correctly predicted.

CONCLUSIONS

Genotypic predictions of the susceptibility of M. tuberculosis to first-line drugs were found to be correlated with phenotypic susceptibility to these drugs. (Funded by the Bill and Melinda Gates Foundation and others.).

Secretome profile analysis of multidrug-resistant, monodrug-resistant and drug-susceptible Mycobacterium tuberculosis

The emergence of drug-resistant tuberculosis has generated great concern in the control of tuberculosis and HIV/TB patients have established severe complications that are difficult to treat. Although, the gold standard of drug-susceptibility testing is highly accurate and efficient, it is time-consuming. Diagnostic biomarkers are, therefore, necessary in discriminating between infection from drug-resistant and drug-susceptible strains. One strategy that aids to effectively control tuberculosis is understanding the function of secreting proteins that mycobacteria use to manipulate the host cellular defenses. In this study, culture filtrate proteins from Mycobacterium tuberculosis H37Rv, isoniazid-resistant, rifampicin-resistant and multidrug-resistant strains were gathered and profiled by shotgun-proteomics technique. Mass spectrometric analysis of the secreted proteome identified several proteins, of which 837, 892, 838 and 850 were found in M. tuberculosis H37Rv, isoniazid-resistant, rifampicin-resistant and multidrug-resistant strains, respectively. These proteins have been implicated in various cellular processes, including biological adhesion, biological regulation, developmental process, immune system process localization, cellular process, cellular component organization or biogenesis, metabolic process, and response to stimulus. Analysis based on STITCH database predicted the interaction of DNA topoisomerase I, 3-oxoacyl-(acyl-carrier protein) reductase, ESAT-6-like protein, putative prophage phiRv2 integrase, and 3-phosphoshikimate 1-carboxyvinyltransferase with isoniazid, rifampicin, pyrazinamide, ethambutol and streptomycin, suggesting putative roles in controlling the anti-tuberculosis ability. However, several proteins with no interaction with all first-line anti-tuberculosis drugs might be used as markers for mycobacterial identification.

Nano-Formulation of Ethambutol with Multifunctional Graphene Oxide and Magnetic Nanoparticles Retains Its Anti-Tubercular Activity with Prospects of Improving Chemotherapeutic Efficacy

Tuberculosis (TB) is a dreadful bacterial disease, infecting millions of human and cattle every year worldwide. More than 50 years after its discovery, ethambutol continues to be an effective part of the World Health Organization's recommended frontline chemotherapy against TB. However, the lengthy treatment regimens consisting of a cocktail of antibiotics affect patient compliance. There is an urgent need to improve the current therapy so as to reduce treatment duration and dosing frequency. In this study, we have designed a novel anti-TB multifunctional formulation by fabricating graphene oxide with iron oxide magnetite nanoparticles serving as a nano-carrier on to which ethambutol was successfully loaded. The designed nanoformulation was characterised using various analytical techniques. The release of ethambutol from anti-TB multifunctional nanoparticles formulation was found to be sustained over a significantly longer period of time in phosphate buffer saline solution at two physiological pH (7.4 and 4.8). Furthermore, the nano-formulation showed potent anti-tubercular activity while remaining non-toxic to the eukaryotic cells tested. The results of this in vitro evaluation of the newly designed nano-formulation endorse its further development in vivo.

Band pattern analysis of mutations in rifampicin resistance strain of Mycobacterium tuberculosis by Line Probe assay in patients from Delhi, India

BACKGROUND

The GenoType MTBDRplus, a commercial Line Probe Assay (LPA) kit from Hain Lifescience, Germany, is endorsed by India's RNTCP Program for diagnosis of DRTB cases among smear-positive sputum samples. Although the LPA has been studied in several laboratories, there is a wide variation in existing M. tuberculosis strains across the globe, and false results can occur due to the presence of unique genetic mutations in different settings.

AIM AND OBJECTIVE

An attempt was made to carry out band pattern analysis using LPA and also to observe uncommon mutations in MDR strains.

MATERIALS AND METHODS

Sputum samples were collected from MDR suspects and transported to intermediate reference laboratory (IRL) at New Delhi Tuberculosis Centre in Delhi. Sputum decontamination, DNA extraction, amplification, hybridization, and band pattern analysis of Line Probe assay strips was performed as per manufacturer's instructions.

RESULTS

Among the 3000 samples with interpretable LPA strips, rifampicin drug resistance with or without isoniazid was observed in 600 samples. The most common mutation detected by LPA in the rpoB gene was Ser516Leu (29.0%). Novel mutations reported in this study include mutation from CAG (Gin) to CAT (His) at codon 517, AGC (Ser)-AGG (Arg) at codon 512, ACA (Thr) to GCA (Ala) at codon 526, TTG (Leu)-CTG (Leu)^s at codon 524.

CONCLUSION

High frequencies of uncommon mutations in rpoB gene by LPA were observed, highlighting possibility of those in-silico detected mutations that may not impart phenotypic resistance further.

The Rate of Drug-Resistant Tuberculosis in Korean Children and Adolescents Since 2007

The incidence of drug-resistant tuberculosis (DR-TB) in pediatric populations is a critical indicator of national TB management and treatment strategies. Limited data exist regarding the rate of pediatric DR-TB. In this study, we aimed to analyze the status of DR-TB in Korean children from 2007 to 2013. We analyzed specimens submitted to the Korean Institute of Tuberculosis using Mycobacterium tuberculosis culture and drug susceptibility tests (DSTs) from January 2007 through December 2013. Specimens from patients ≤ 19 years of age were included. Among the 2,690 cases, 297 cases were excluded because of insufficient data, leaving 2,393 cases for the final analysis. In total, resistance to one or more TB drugs was 13.5%. The resistance rates of each of the drugs were as follows: isoniazid (INH) 10.2%, rifampin (RFP) 5.1%, ethambutol (EMB) 3.7%, and pyrazinamide (PZA) 3.1%. The resistance rate of multidrug-resistant TB (MDR-TB) was 4.2%, and that of extensively drug-resistant TB (XDR-TB) was 0.8%. The overall drug resistance rate demonstrated significant increase throughout the study period (P < 0.001) but showed no significant difference compared to previous study from 1999 to 2007. The drug resistance rate of PZA in ≤ 15 years of age group was significantly greater than that of > 15 years (P < 0.001). The drug resistance rate has increased throughout the study period.

Natural Terpenes Influence the Activity of Antibiotics against Isolated Mycobacterium tuberculosis

OBJECTIVE

In this study, we aimed to describe the influence of natural terpenes on the antimycobacterial activity of first-line tuberculostatic drugs against isolated Mycobacterium tuberculosis.

MATERIALS AND METHODS

The natural terpenes used in this study were R-limonene, S-limonene, myrcene, sabinene, α-pinene, and β-elemene. The values of the minimum inhibitory concentration (MIC) for these terpenes, as well as for combinations of terpenes with tuberculostatic antibiotics (ethambutol, isoniazid, and rifampicin), were determined using a tube log2 dilution method in the range of 125-0.059 µg/mL.

RESULTS

S-limonene had a strong synergistic effect with all tested antibiotics (MIC decreased from 16 to 0.475 µg/mL for ethambutol, from 16 to 0.237 µg/mL for rifampicin, and from 32 to 0.475 µg/mL for isoniazid). Combinations of myrcene, R-limonene, β-elemene, and sabinene with tuberculostatic antibiotics resulted in a decreased MIC of the antibiotics (from 3.9 to 0.475 µg/mL for ethambutol, from 15 to 0.475 µg/mL for isoniazid, and from 0.475 to 0.237 µg/mL for rifampicin) while combinations of α-pinene with ethambutol and isoniazid resulted in increased MIC values (from 16 to 125 µg/mL for ethambutol, and from 32 to 125 µg/mL for isoniazid). Rifampicin had a synergistic increase in activity with all the tested compounds.

CONCLUSIONS

Our study showed that terpenes enhance the activity of tuberculostatic antibiotics.

Mechanisms of first-line antimicrobial resistance in multi-drug and extensively drug resistant strains of Mycobacterium tuberculosis in KwaZulu-Natal, South Africa

BACKGROUND

In South Africa, drug resistant tuberculosis is a major public health crisis in the face of the colossal HIV pandemic.

METHODS

In an attempt to understand the distribution of drug resistance in our setting, we analysed the rpoB, katG, inhA, pncA and embB genes associated with resistance to key drugs used in the treatment of tuberculosis in clinical isolates of Mycobacterium tuberculosis in the KwaZulu-Natal province.

RESULTS

Classical mutations were detected in the katG, inhA and embB genes associated with resistance to isoniazid and ethambutol. Diverse mutations were recorded in the multidrug resistant (MDR) and extensively drug resistant (XDR) isolates for the rpoB and pncA gene associated with resistance to rifampicin and pyrazinamide.

CONCLUSIONS

M.tuberculosis strains circulating in our setting display a combination of previously observed mutations, each mediating resistance to a different drug. The MDR and XDR TB isolates analysed in this study displayed classical mutations linked to INH and EMB resistance, whilst diverse mutations were linked to RIF and PZA resistance. The similarity of the XDR strains confirms reports of the clonality of the XDR epidemic. The successful dissemination of the drug resistant strains in the province underscores the need for rapid diagnostics to effectively diagnose drug resistance and guide treatment.

iniBAC induction Is Vitamin B12- and MutAB-dependent in Mycobacterium marinum

Tuberculosis can be treated with a 6-month regimen of antibiotics. Although the targets of most of the first-line antibiotics have been identified, less research has focused on the intrabacterial stress responses that follow upon treatment with antibiotics. Studying the roles of these stress genes may lead to the identification of crucial stress-coping mechanisms that can provide additional drug targets to increase treatment efficacy. A three-gene operon with unknown function that is strongly up-regulated upon treatment with isoniazid and ethambutol is the iniBAC operon. We have reproduced these findings and show that iniBAC genes are also induced in infected host cells, although with higher variability. Next, we set out to elucidate the genetic network that results in iniBAC induction in Mycobacterium marinum By transposon mutagenesis, we identified that the operon is highly induced by mutations in genes encoding enzymes of the vitamin B12 biosynthesis pathway and the vitamin B12-dependent methylmalonyl-CoA-mutase MutAB. Lipid analysis showed that a mutA::tn mutant has decreased phthiocerol dimycocerosates levels, suggesting a link between iniBAC induction and the production of methyl-branched lipids. Moreover, a similar screen in Mycobacterium bovis BCG identified that phthiocerol dimycocerosate biosynthesis mutants cause the up-regulation of iniBAC genes. Based on these data, we propose that iniBAC is induced in response to mutations that cause defects in the biosynthesis of methyl-branched lipids. The resulting metabolic stress caused by these mutations or caused by ethambutol or isoniazid treatment may be relieved by iniBAC to increase the chance of bacterial survival.

Metal II complexes of ethambutol as good enzyme inhibitor and promising antioxidant

Ethambutoldihydrogenchloride (EMB) with chemical formula C10H24N2O2.2HCl is ethane-1,2-diamine in which one hydrogen attached to each of the nitrogen is substituted by a 1-hydroxybutan-2-yl group (S,S-configuration). It is an FDA approved drug and has been used for treatment of tuberculosis since 1960's. Prolong use of EMB has a side effect of visual impairment and in literature it is related with the depletion of Zn metal from the body. As it is a good chelating agent, many metal II complexes have been synthesized with anti-tubercular activity. The purpose of this work was to synthesize metal II complexes of EMB and to evaluate their antioxidant activity along with enzyme inhibition activity (acetylcholine esterase and protease). The metals used for complex formation were Co, Zn, Fe, Cu and Ni. IR spectral data and physical parameters supported the complex formation. The obtained results showed the synthesized complexes as notable antioxidants and enzyme inhibitors.

L-form transformation phenomenon in Mycobacterium tuberculosis associated with drug tolerance to ethambutol

OBJECTIVE/BACKGROUND

Cell wall-deficient bacterial forms (L-forms) may occur along with resistance to factors that trigger their appearance. It is of interest to study the relationship between the L-form transformation of Mycobacterium tuberculosis and the exhibition of drug tolerance to ethambutol (EMB), an inhibitor of cell wall synthesis.

METHODS

L-form variant was produced from a sensitive EMB strain of M. tuberculosis through a cryogenic stress treatment protocol and was subsequently cultivated in Middlebrook 7H9 semisolid medium, containing EMB in a minimal inhibitory concentration of 2mg/L. Susceptibility to EMB of the parental strain and its L-form variant was evaluated phenotypically and using polymerase chain reaction-restriction fragment length polymorphism assay targeting a mutation in the embB306 gene fragment.

RESULTS

In contrast to the sensitivity to EMB of the parental strain, its L-form variant showed phenotypic resistance to high concentrations of EMB (16mg/L), but the mutation in embB306 was not found. Electron microscopy observation of the L-form variant showed a heterogenic population of bacteria, with different degrees of cell wall deficiency, as well as cells of protoplastic type without cell walls. Of special interest were the observed capsule-like structures around the L-form cells and the biofilm-like matrix produced by the L-form population.

CONCLUSION

We suggest that the expression of phenotypic resistance to EMB in M. tuberculosis can be associated with alterations or loss of cell walls in L-form bacteria, respectively, which results in a lack of a specific target for EMB action. In addition, production of capsule-like structures and biofilm matrix by L-forms could contribute to their resistance and survival in the presence of antibacterial agents.

Epidemiological Trends of Drug-Resistant Tuberculosis in China From 2007 to 2014: A Retrospective Study

The emergence and spread of drug-resistant tuberculosis (DR-TB) has become the major concern in global TB control nowadays due to its limited therapy options and high mortality. A comprehensive evaluation for the epidemiological trends of DR-TB in mainland China, of which TB incidences remain high, is essential but lacking. This study aimed to describe the trends of DR-TB overtime, especially multidrug-resistant TB (MDR-TB); and to identify unique characteristics of MDR-TB cases compared with drug-susceptible TB cases in Mainland China. We retrospectively analyzed surveillance data collected from 36 TB prevention and control institutions in Shandong Province, China over an 8-year period. Unique characteristics of MDR-TB were identified; Chi-square test for trends and linear regression were used to assess the changes in proportions of different resistance patterns overtime. The overall MDR rate was 6.2% in our sample population. There were no statistically significant changes in the percentage of drug-susceptible, isoniazid (INH) resistance, ethambutol (EMB) resistance, streptomycin (SM) resistance, and MDR TB during our study period except that the overall rifampin (RFP) resistance and rifampin monoresistance (RMR) increased at a yearly rate of 0.2% and 0.1%, respectively. Among those with known treatment histories, a higher MDR rate of 8.7% was observed, in which 53.9% were primary MDR-TB patients, and this rate was increasing at a yearly rate of 4.1% over our study period. MDR-TB patients were more likely to be female (odds ratio [OR], 1.23; 95% confidence interval [CI], 1.05-1.34), aged 25 to 44 years (OR, 1.67; 95%CI, 1.45-1.93), retreated (OR, 11.95; 95%CI, 9.68-14.76), having prior TB contact (OR, 1.89; 95%CI, 1.19-2.78) and having cavity (OR, 1.57; 95%CI 1.36-1.81), or bilateral disease (OR, 1.45; 95%CI 1.19-1.76) on chest radiology. Persistent high levels of MDR-TB, increasing rates of primary MDR-TB and RMR characterize DR-TB cases in mainland China; community-acquired drug resistance may be one of the most modifiable factors in future TB control strategies.

Diagnosis of Drug Resistance to Fluoroquinolones, Amikacin, Capreomycin, Kanamycin and Ethambutol with Genotype MTBDRsl Assay: a Meta-Analysis

BACKGROUND

The Genotype MTBDRsl is a new-generation PCR-based line-probe assay for rapid identification of the resistance to the second-line antituberculosis drugs with a single strip. The aim of this meta-analysis was to evaluate the performance of Genotype MTBDRsl in detecting drug resistance to fluoroquinolones, amikacin, capreomycin, kanamycin and ethambutol in comparison with the phenotypic drug susceptibility test.

DESIGN

We searched Pubmed, Embase and the Cochrane Library and calculated the sensitivity, the specificity, the positive likelihood ratio (PLR), negative likelihood ratio (NLR), diagnostic odds ratio (DOR), corresponding 95% confidence interval (CI), and the area under the summary receiver operating characteristic (SROC) curves (AUC), and tested heterogeneity in accuracy estimates with the Spearman correlation coefficient and Chi-square.

RESULTS

The summarized sensitivity (95% CI), specificity (95% CI), and AUC (standard error) were 0.869 (0.847-0.890), 0.973 (0.965-0.979) and 0.9690 (0.0188) for fluoroquinolones, 0.868 (0.829-0.900), 0.998 (0.994-0.999) and 0.9944 (0.0050) for amikacin, 0.879 (0.838-0.914), 0.970 (0.958-0.978) and 0.9791 (0.0120) for capreomycin, 0.501 (0.461-0.541), 0.991 (0.983-0.996) and 0.9814 (0.0114) for kanamycin and 0.686 (0.663-0.709), 0.871 (0.852-0.888) and 0.7349 (0.0639) for ethambutol, respectively.

CONCLUSION

The genotype MTBDRsl demonstrate excellent accuracy for detecting drug resistance to fluoroquinolones, amikacin, and capreomycin, but it may not be an appropriate choice for detection of kanamycin and ethambutol.

Re-evaluation of the critical concentration for ethambutol antimicrobial sensitivity testing on the MGIT 960

The critical concentration (CC) for ethambutol testing on the Bactec MGIT 960 M. tuberculosis susceptibility testing has been questioned in recent publications. In this study, we correlate susceptibility results from the Bactec 460, MGIT 960 and embB gene sequencing to determine if the Bactec MGIT 960 adequately detects ethambutol resistance. We discovered discrepancies between the methods that highlight a need to re-evaluate ethambutol susceptibility testing recommendations, namely by considering lowering currently recommended CC on the MGIT 960. Further studies on the clinical significance of low-level ethambutol resistance are also required.

Evaluation of BACTEC MGIT 960 system for testing susceptibility of Mycobacterium tuberculosis to first-line drugs in China

BACKGROUND

The purpose of this study was to evaluate the performance of the BACTEC MGIT 960 (M960) system compared with the proportion method (PM) on Löwenstein-Jensen (L-J) medium in a peripheral laboratory in China for the testing of Mycobacterium tuberculosis (MTB) susceptibility to streptomycin (SM), isoniazid (INH) rifampicin (RIF) and ethambutol (EMB) a combination known as SIRE.

METHODS

The susceptibility of 205 clinical isolates of MTB to SM, INH, RIF and EMB was performed with the M960 system. The drugs were tested at the following concentrations: 1.0 µg/ml for SM, 0.1 µg/ml for INH, 1.0 µg/ml for RIF, and 5.0 µg/ml for EMB. The results were compared with those obtained by the L-J PM. The L-J PM at an arbiter site was used to resolve any discordant results.

RESULTS

The overall consistency was 96.6% and concordance values were 95.6% for SM, 97.6% for INH, 98.0% for RIF and 95.1% for EMB. The overall sensitivity, specificity, positive predictive value (PPV) and negative predictive value (NPV) of the M960 system for PM (the standard method) was 95.6%, 97.3%, 96.2% and 96.9% respectively, and the sensitivity were 93.3% for SM, 96.9% for INH, 97.4% for RIF and 94.6% for EMB, the specificity were 96.9% for SM, 98.2% for INH, 98.4% for RIF and 95.5% for EMB, the PPV were 94.6% for SM, 97.9% for INH, 97.4% for RIF and 94.6% for EMB, the NPV were 96.2% for SM, 97.3% for INH, 98.4% for RIF and 95.5% for EMB. The turnaround time with the M960 system (median 8.0 days, ranged from 5 to 14 days) was significantly shorter than that with the PM (28 days or 42 days).

CONCLUSION

There was a substantial degree of agreement between the two methods. The M960 system was a reliable and rapid method for SIRE susceptibility testing of tuberculosis in China.

Diagnostic accuracy of a molecular drug susceptibility testing method for the antituberculosis drug ethambutol: a systematic review and meta-analysis

Ethambutol (EMB) is a first-line antituberculosis drug; however, drug resistance to EMB has been increasing. Molecular drug susceptibility testing (DST), based on the embB gene, has recently been used for rapid identification of EMB resistance. The aim of this meta-analysis was to establish the accuracy of molecular assay for detecting drug resistance to EMB. PubMed, Embase, and Web of Science were searched according to a written protocol and explicit study selection criteria. Measures of diagnostic accuracy were pooled using a random effects model. A total of 34 studies were included in the meta-analysis. The respective pooled sensitivities and specificities were 0.57 and 0.93 for PCR-DNA sequencing that targeted the embB 306 codon, 0.76 and 0.89 for PCR-DNA sequencing that targeted the embB 306, 406, and 497 codons, 0.64 and 0.70 for detecting Mycobacterium tuberculosis isolates, 0.55 and 0.78 for detecting M. tuberculosis sputum specimens using the GenoType MTBDRsl test, 0.57 and 0.87 for pyrosequencing, and 0.35 and 0.98 for PCR-restriction fragment length polymorphism. The respective pooled sensitivities and specificities were 0.55 and 0.92 when using a lower EMB concentration as the reference standard, 0.67 and 0.73 when using a higher EMB concentration as the reference standard, and 0.60 and 1.0 when using multiple reference standards. PCR-DNA sequencing using multiple sites of the embB gene as detection targets, including embB 306, 406, and 497, can be a rapid method for preliminarily screening for EMB resistance, but it does not fully replace phenotypic DST. Of the reference DST methods examined, the agreement rates were the best using MGIT 960 for molecular DST and using the proportion method on Middlebrook 7H10 media.

Isoniazid mediates the CYP2B6*6 genotype-dependent interaction between efavirenz and antituberculosis drug therapy through mechanism-based inactivation of CYP2A6

Efavirenz is commonly used to treat patients coinfected with human immunodeficiency virus and tuberculosis. Previous clinical studies have observed paradoxically elevated efavirenz plasma concentrations in patients with the CYP2B6*6/*6 genotype (but not the CYP2B6*1/*1 genotype) during coadministration with the commonly used four-drug antituberculosis therapy. This study sought to elucidate the mechanism underlying this genotype-dependent drug-drug interaction. In vitro studies were conducted to determine whether one or more of the antituberculosis drugs (rifampin, isoniazid, pyrazinamide, or ethambutol) potently inhibit efavirenz 8-hydroxylation by CYP2B6 or efavirenz 7-hydroxylation by CYP2A6, the main mechanisms of efavirenz clearance. Time- and concentration-dependent kinetics of inhibition by the antituberculosis drugs were determined using genotyped human liver microsomes (HLMs) and recombinant CYP2A6, CYP2B6.1, and CYP2B6.6 enzymes. Although none of the antituberculosis drugs evaluated at up to 10 times clinical plasma concentrations were found to inhibit efavirenz 8-hydroxylation by HLMs, both rifampin (apparent inhibition constant [Ki] = 368 μM) and pyrazinamide (Ki = 637 μM) showed relatively weak inhibition of efavirenz 7-hydroxylation. Importantly, isoniazid demonstrated potent time-dependent inhibition of efavirenz 7-hydroxylation in both HLMs (inhibitor concentration required for half-maximal inactivation [KI] = 30 μM; maximal rate constant of inactivation [kinact] = 0.023 min(-1)) and recombinant CYP2A6 (KI = 15 μM; kinact = 0.024 min(-1)) and also formed a metabolite intermediate complex consistent with mechanism-based inhibition. Selective inhibition of the CYP2B6.6 allozyme could not be demonstrated for any of the antituberculosis drugs using either recombinant enzymes or CYP2B6*6 genotype HLMs. In conclusion, the results of this study identify isoniazid as the most likely perpetrator of this clinically important drug-drug interaction through mechanism-based inactivation of CYP2A6.