Inter- and Intra-Assay Reproducibility of Microplate Alamar Blue Assay Results for Isoniazid, Rifampicin, Ethambutol, Streptomycin, Ciprofloxacin, and Capreomycin Drug Susceptibility Testing of Mycobacterium tuberculosis

Proficiency of phenotypic drug susceptibility testing for Mycobacterium tuberculosis in China, 2008-2021

To analyze the results of proficiency testing for anti-tuberculosis drug susceptibility testing (DST) in China. Number of laboratory participating the proficiency testing performed DST, and the sensitivity, specificity, reproducibility, and accordance rate were calculated from data of 13 rounds proficiency testing results for DST from 2008 to 2021. A total of 30 and 20 strains of Mycobacterium tuberculosis with known susceptibility results were sent to each laboratory in 2008 to 2019, 2020 and 2021, respectively. The number of participating laboratories ranged from 30 in 2009 to 546 in 2021. L-J DST was the predominant method. The specificity presented relatively higher than sensitivity. Improvement of specificity were observed for all drugs through the years, while sensitivity did not show improvement for amikacin and capreomycin. Accordance rate of pyrazinamide and kanamycin and reproducibility of capreomycin and pyrazinamide were not significantly improved through the years. Most of the participating laboratories significantly improved the quality of their DST through the consecutive rounds of proficiency testing except for second-line injectable drugs and pyrazinamide. The results highlight the importance of developing novel and/or improving existing methods for phenotypic DST for certain drugs.

Lipids Extracted from Mycobacterial Membrane and Enveloped PLGA Nanoparticles for Encapsulating Antibacterial Drugs Elicit Synergistic Antimicrobial Response against Mycobacteria

Tuberculosis (TB) is a chronic disease caused byMycobacterium tuberculosis (Mtb), which shows a long treatment cycle often leads to drug resistance, making treatment more difficult. Immunogens present in the pathogen's cell membrane can stimulate endogenous immune responses. Therefore, an effective lipid-based vaccine or drug delivery vehicle formulated from the pathogen's cell membrane can improve treatment outcomes. Herein, we extracted and characterized lipids fromMycobacterium smegmatis, and the extracts contained lipids belonging to numerous lipid classes and compounds typically found associated with mycobacteria. The extracted lipids were used to formulate biomimetic lipid reconstituted nanoparticles (LrNs) and LrNs-coated poly(lactic-co-glycolic acid) nanoparticles (PLGA-LrNs). Physiochemical characterization and results of morphology suggested that PLGA-LrNs exhibited enhanced stability compared with LrNs. And both of these two types of nanoparticles inhibited the growth of M. smegmatis. After loading different drugs, PLGA-LrNs containing berberine or coptisine strongly and synergistically prevented the growth of M. smegmatis. Altogether, the bacterial membrane lipids we extracted with antibacterial activity can be used as nanocarrier coating for synergistic antibacterial treatment of M. smegmatis─an alternative model of Mtb, which is expected as a novel therapeutic system for TB treatment.

Design, Synthesis and In vitro Antitubercular Effect of New Chalcone Derivatives Coupled with 1,2,3-Triazoles: A Computational Docking Techniques

A very interesting foundation for this study is the creation of new methods for modifying compounds with a 1,2,3-triazole and chalcone scaffolds, as these compounds are significant in organic synthesis, particularly in the synthesis of bioactive organic compounds. To contribute to the development of an efficient method for the conversion of antimicrobial and antituberculosis heterocyclics, a novel series of cyclohepta pyridinone fused 1,2,3-triazolyl chalcones were designed and synthesized. All the newly prepared scaffolds were characterized by FT-IR, NMR (1H & 13C) and mass spectrometry. Among the tested compounds, hybrids 8b, 8d, and 8f exhibited exceptional antibacterial susceptibilities with zone of inhibition 27.84±0.04, 32.27±0.02, and 38.26±0.01 mm against the tested E. faecalis bacteria, whereas 8d had better antitubercular potency against M. tuberculosis H37Rv strain with MIC value 5.25 μg/mL, compared to Streptomycin [MIC=5.01 μg/mL]. All the synthesized compounds were initially assessed in silico against the targeted protein i. e., DprE1 that indicated compound 8d, 8f and 8h along with several other 1,2,3-triazole compounds as possible inhibitors. Based on docking results, 8d showed that the amino acids His74(A), Lys76(A), Cys332(A), Asp331(A), Val307(A), Tyr357(A), Met226(A), Gln276(A), Gly75(A), Peo58(A), Leu259(A), and Lys309(A) exhibited highly stable binding to DprE1 receptor of Mycobacterium tuberculosis (PDB: 4G3 U). Moreover, these scaffolds physicochemical characteristics, filtration molecular properties, assessment of toxicity, and bioactivity scores were assessed in relation to ADME (absorption, distribution, metabolism, and excretion).

Microfluidics produced ATRA-loaded PLGA NPs reduced tuberculosis burden in alveolar epithelial cells and enabled high delivered dose under simulated human breathing pattern in 3D printed head models

Tuberculosis, caused by Mycobacterium tuberculosis (Mtb), is second only to COVID-19 as the top infectious disease killer worldwide. Multi-drug resistant TB (MDR-TB) may arise because of poor patient adherence to medications due to lengthy treatment duration and side effects. Delivering novel host directed therapies (HDT), like all trans retinoic acid (ATRA) may help to improve drug regimens and reduce the incidence of MDR-TB. Local delivery of ATRA to the site of infection leads to higher bioavailability and reduced systemic side effects. ATRA is poorly soluble in water and has a short half-life in plasma. Therefore, it requires a formulation step before it can be administered in vivo. ATRA loaded PLGA nanoparticles suitable for nebulization were manufactured and optimized using a scalable nanomanufacturing microfluidics (MF) mixing approach (MF-ATRA-PLGA NPs). MF-ATRA-PLGA NPs demonstrated a dose dependent inhibition of Mtb growth in TB-infected A549 alveolar epithelial cell model while preserving cell viability. The MF-ATRA-PLGA NPs were nebulized with the Aerogen Solo vibrating mesh nebulizer, with aerosol droplet size characterized using laser diffraction and the estimated delivered dose was determined. The volume median diameter (VMD) of the MF-ATRA-PLGA NPs was 3.00 ± 0.18 μm. The inhaled dose delivered in adult and paediatric 3D printed head models under a simulated normal adult and paediatric breathing pattern was found to be 47.05 ± 3 % and 20.15 ± 3.46 % respectively. These aerosol characteristics of MF-ATRA-PLGA NPs supports its suitability for delivery to the lungs via inhalation. The data generated on the efficacy of an inhalable, scalable and regulatory friendly ATRA-PLGA NPs formulation provides a foundation on which further pre-clinical testing can be built. Overall, the results of this project are promising for future research into ATRA loaded NPs formulations as inhaled host directed therapies for TB.

The importance of heteroresistance and efflux pumps in bedaquiline-resistant Mycobacterium tuberculosis isolates from Iran

BACKGROUND

Tuberculosis (TB) continues to pose a threat to communities worldwide and remains a significant public health issue in several countries. We assessed the role of heteroresistance and efflux pumps in bedaquiline (BDQ)-resistant Mycobacterium tuberculosis isolates.

METHODS

Nineteen clinical isolates were included in the study, of which fifteen isolates were classified as MDR or XDR, while four isolates were fully susceptible. To evaluate BDQ heteroresistance, the Microplate Alamar Blue Assay (MABA) method was employed. For screening mixed infections, MIRU-VNTR was performed on clinical isolates. Mutations in the atpE and Rv0678 genes were determined based on next-generation sequencing data. Additionally, real-time PCR was applied to assess the expression of efflux pump genes in the absence and presence of verapamil (VP).

RESULTS

All 15 drug-resistant isolates displayed resistance to BDQ. Among the 19 total isolates, 21.05% (4/19) exhibited a heteroresistance pattern to BDQ. None of the isolates carried a mutation of the atpE and Rv0678 genes associated with BDQ resistance. Regarding the MIRU-VNTR analysis, most isolates (94.73%) showed the Beijing genotype. Fifteen (78.9%) isolates showed a significant reduction in BDQ MIC after VP treatment. The efflux pump genes of Rv0676c, Rv1258c, Rv1410c, Rv1634, Rv1819, Rv2459, Rv2846, and Rv3065 were overexpressed in the presence of BDQ.

CONCLUSIONS

Our results clearly demonstrated the crucial role of heteroresistance and efflux pumps in BDQ resistance. Additionally, we established a direct link between the Rv0676c gene and BDQ resistance. The inclusion of VP significantly reduced the MIC of BDQ in both drug-susceptible and drug-resistant clinical isolates.

Identification of Mutations Associated With Macozinone-Resistant in Mycobacterium Tuberculosis

Novel anti-tuberculosis drug macozinone (MCZ) is identified as a drug candidate and is currently under clinical development for the treatment of tuberculosis. However, the mutations conferring resistance to MCZ remain inadequately characterized. In this study we investigated resistant mutations to the MCZ through de novo resistance selection in vitro. This was accomplished by passing the Mycobacterium tuberculosis H37Rv on solid agar plates, which were infused with the antibiotic. Through whole genome sequencing and targeted PCR genomic resistance conferring SNPs were catalogued, and the resistant phenotype was analyzed by MABA test. Of MCZ-resistant clones obtained in vitro the mutation of C387S in dprE1 is only observed in high-level resistant clones (MIC₉₀ > 500 ng/mL) indicating that C387S mutation is directly related to high-level MCZ-resistance. In addition, high-level resistance to MCZ can occur in clone grew on agar plates infused with low concentration MCZ, which means low concentration MCZ induction can produce high-level drug-resistance and it is easy to produce high-level MCZ-resistance. We also found two new mutations (G61A and G248A) in dprE1 for the first time. The MIC₉₀ of other clones except the clones carrying the C387S mutation was at the same level (20 ng/mL > MIC₉₀ > 2 ng/mL). Of low-level resistant clones other gene mutations involved in drug efflux or membrane permeability were found (pepQ, Rv0678, arsC, etc.), with highest mutation frequency in Rv0678 (50/64, 78.12%). It suggests that there may be new mechanisms independent of dprE1 mutations.

A Covalently Crosslinked Ink for Multimaterials Drop-on-Demand 3D Bioprinting of 3D Cell Cultures

In vitro 3D cell models have been accepted to better recapitulate aspects of in vivo organ environment than 2D cell culture. Currently, the production of these complex in vitro 3D cell models with multiple cell types and microenvironments remains challenging and prone to human error. Here, a versatile ink comprising a 4-arm poly(ethylene glycol) (PEG)-based polymer with distal maleimide derivatives as the main ink component and a bis-thiol species as the activator that crosslinks the polymer to form the hydrogel in less than a second is reported. The rapid gelation makes the polymer system compatible with 3D bioprinting. The ink is combined with a novel drop-on-demand 3D bioprinting platform, designed specifically for producing 3D cell cultures, consisting of eight independently addressable nozzles and high-throughput printing logic for creating complex 3D cell culture models. The combination of multiple nozzles and fast printing logic enables the rapid preparation of many complex 3D cell cultures comprising multiple hydrogel environments in one structure in a standard 96-well plate format. The platform's compatibility for biological applications is validated using pancreatic ductal adenocarcinoma cancer (PDAC) and human dermal fibroblast cells with their phenotypic responses controlled by tuning the hydrogel microenvironment.

Detecting Ethambutol Resistance in Mycobacterium tuberculosis Isolates in China: A Comparison Between Phenotypic Drug Susceptibility Testing Methods and DNA Sequencing of embAB

With the increasing incidence of drug-resistant tuberculosis (DR-TB), determining a rapid and accurate drug susceptibility testing (DST) method to identify ethambutol (EMB) resistance in Mycobacterium tuberculosis has become essential for patient management in China. Herein, we evaluated the correlation between three phenotypic DST methods, namely, proportion method (PM), MGIT 960 system, and microplate alamar Blue assay (MABA), and DNA sequencing of embAB in 118 M. tuberculosis isolates from China. When the results of the phenotypic DST methods were compared with those of DNA sequencing, the overall agreement and kappa values of the PM, MGIT 960 system, and MABA were 81.4% and 0.61, 77.1% and 0.55, and 84.7% and 0.67, respectively. The agreement for EMB resistance between MABA and PM was significantly higher than that between the MGIT 960 system and PM (P = 0.02). Moreover, among the isolates with detectable embAB mutations, 97.2% (70/72 isolates) harbored mutations in embB. The analysis of embB mutations predicted EMB resistance with 81.3% sensitivity, 86.8% specificity, and 83.1% accuracy. Thus, MABA may be a better phenotypic DST method for detecting EMB resistance. DNA sequencing of embB may be useful for the early identification of EMB resistance and the consequent optimization of the treatment regimen.

Role of esxG and esxH Genes in Drug-Resistant Mycobacterium

Tuberculosis drug resistance (DR) is a global problem that is not fully elucidated. Previously, overexpression of esxG and esxH genes was reported in a multidrug-resistant (MDR) Mycobacterium tuberculosis isolate compared with a reference H37Rv strain. To evaluate the roles of esxG and esxH in DR, analysis of their regulatory and coding sequences in sensitive and resistant strains was performed, and the expression levels of their transcriptional regulators IdeR, Zur, and MntR were evaluated. esxG and esxH were expressed heterologously using mycobacterial constructs, and the orthologs Msmeg_0620 and Msmeg_0621 were attenuated in Mycobacterium smegmatis by antisense knockdown. We found no differences in the regulatory and coding sequences of esxG and esxH between the sensitive strain and the MDR isolate. Expression analysis of transcriptional regulators showed that ideR was upregulated in isoniazid (INH)-resistant isolates; in addition, growth inhibition of the M. smegmatis strain was observed in the presence of rifampicin (RIF) and INH when esxG and esxH were expressed heterologously, while faster growth in the presence of RIF was observed when the orthologs were attenuated. In conclusion, the expression of esxG and esxH altered the growth of Mycobacterium in the presence of INH and RIF, suggesting a potential association with DR.

Scrutinizing the drug resistance mechanism of multi- and extensively-drug resistant Mycobacterium tuberculosis: mutations versus efflux pumps

Background

In order to shorten the course of treatment and its effectiveness, it is essential to gain an in-depth insight into the drug resistance mechanisms of Mycobacterium tuberculosis (M. tuberculosis).

Methods

In this study, we evaluated the contribution of 26 drug efflux pumps plus target gene mutations to the drug resistance levels in multi-drug resistant (MDR)/pre-extensively drug-resistant (pre-XDR)/extensively drug-resistant (XDR) and mono-drug resistant clinical isolates of M. tuberculosis. The panels of 25 M. tuberculosis clinical strains were characterized for drug resistance-associated mutations with whole-genome sequencing and antibiotic profiles in the presence and absence of efflux inhibitor verapamil (VP).

Results

Different MICs were observed for the same target gene mutations. Out of the 16 MDR/pre-XDR/XDR isolates, 6 (37.5%) and 3 (18.8%) isolates demonstrated a significant decrease in rifampicin (RIF) MIC and isoniazid (INH) MIC due to the VP exposure (64 μg/mL), respectively. Susceptibility to RIF was fully restored in two isolates after VP exposure. Moreover, the efflux pump genes of Rv2938, Rv2936, Rv1145, Rv1146, Rv933, Rv1250, Rv876, Rv2333, Rv2459, Rv849, and Rv1819 were overexpressed in the presence of anti-TB drugs, showing the contribution of these efflux pumps to the overall resistance phenotype.

Conclusions

Our results clearly showed that efflux systems, besides spontaneous mutations, play a role in the development of INH/RIF resistance. In addition, although VP was effective in reducing the expression of some efflux pumps, it was not very successful at the phenotypic level.

Comparisons of whole-genome sequencing and phenotypic drug susceptibility testing for Mycobacterium tuberculosis causing MDR-TB and XDR-TB in Thailand

Drug-resistant tuberculosis (TB) is a major public health problem. There is little information regarding the genotypic-phenotypic association of anti-TB drugs, especially for second-line drugs. This study compared phenotypic drug susceptibility testing (DST) with predictions based on whole-genome sequencing (WGS) data for 266 Mycobacterium tuberculosis isolates. Phenotypic DST used the standard proportional method. Clinical isolates of M. tuberculosis collected in Thailand between 1998 and 2013 comprised 51 drug-sensitive strains, six mono-resistant strains, two multiple-resistant strains, 88 multi-drug-resistant strains, 95 pre-extensively drug-resistant strains and 24 extensively drug-resistant strains. WGS analysis was performed using the computer programs PhyResSE and TB-Profiler. TB-Profiler had higher average concordance with phenotypic DST than PhyResSE for both first-line (91.96% vs. 91.4%) and second-line (79.67% vs. 78.20%) anti-TB drugs. The average sensitivity for all anti-TB drugs was also higher (83.13% vs. 72.08%) with slightly lower specificity (83.50% vs. 86.68%). Regardless of the program used, isoniazid, rifampicin and amikacin had the highest concordance with phenotypic DST (96.2%, 93.5% and 95.6%, respectively). Ethambutol, ethionamide and fluoroquinolones had the lowest concordance (87.34%, 81.44% and 73.85%, respectively). Concordance rates of ofloxacin (a second-generation fluoroquinolone), levofloxacin, moxifloxacin and gatifloxacin (third- and fourth-generation fluoroquinolones) were 91.79%, 76.62%, 72.64% and 57.35%, respectively. Discordance between phenotypic and WGS-based DSTs may be due, in part, to the choice of critical concentration and variable reproducibility of the phenotypic tests. It may also be due to limitations of the mutation databases (especially for the second-line drugs) and the analysis program used. Mutations related to fluoroquinolone resistance, especially the later generations, need to be identified.

Synthesis and antimycobacterial activity of (+)-usnic acid conjugates

New therapeutics are urgently needed to fight tuberculosis and mycobacteria-related diseases that are a major health hazard especially in poor countries. Natural products have been the source of important antitubercular drugs in the past and still need to receive attention as a potent reservoir of chemical structures. Fifteen known and two new (+)-usnic acid (a benzofurandione formerly isolated from lichens) enamines and hydrazones are here described and tested against sensitive and multidrug-resistant strains of mycobacteria. Among several (+)-usnic acid conjugates, PS14 and PS18 showed potent activity against both susceptible and resistant Mycobacterium tuberculosis strains (MIC values of 1-32 and 2-32 mg/L, respectively) comparable with MIC of other antitubercular drugs already in use for tuberculosis treatment.

Mutations within embCAB Are Associated with Variable Level of Ethambutol Resistance in Mycobacterium tuberculosis Isolates from China

The EmbCAB proteins have been considered a target for ethambutol (EMB). Mutations in embCAB are known to confer most EMB resistance. However, the knowledge about the effects of embCAB mutations on the EMB resistance level and about the role of mutation-mutation interactions is limited in China. Here, we sequenced embCAB among 125 Mycobacterium tuberculosis isolates from China and quantified their EMB MICs by testing growth at 10 concentrations. Furthermore, a multivariate regression model was established to assess the effects of both individual mutations and multiple mutations. Our results revealed that in China, 82.6% of EMB-resistant isolates (71/86 isolates) harbored at least one mutation within embCAB Most of the mutations were located in the embB and embA upstream region. Several individual mutations and multiple mutations within this region contributed to the different levels of EMB resistance. Their effects were statistically significant. Additionally, there was an association between high-level EMB resistance and multiple mutations.

PdtaS Deficiency Affects Resistance of Mycobacteria to Ribosome Targeting Antibiotics

Two-component regulatory systems (TCSSs) are key regulatory elements responsible for the adaptation of bacteria to environmental stresses. A classical TCSS is typically comprised of a sensory histidine kinase and a corresponding response regulator. Here, we used homologous recombination to construct a Mycobacterium smegmatis mutant defective in the synthesis of cytosolic histidine kinase PdtaS (Msmeg_1918). The resulting ΔpdtaS mutant strain was tested in the Phenotype Microarray screening system, which allowed us to identify aminoglycoside antibiotic sensitivity, tetracyclines antibiotic resistance as well as membrane transport and respiration, as the main processes affected by removal of pdtaS. The antibiotic sensitivity profiles were confirmed by survival assessment and complementation studies. To gain insight into the molecular mechanisms responsible for the observed phenotype, we compared ribosomal RNA and protein profiles of the mutant and wild-type strains. We carried out Northern blotting and qRT-PCR to compare rRNA levels and analyzed ribosome sedimentation patterns of the wild-type and mutant strains on sucrose gradients. Isolated ribosomes were further used to estimate relative abundance of individual proteins in the ribosomal subunits using label free mass spectrometry analysis. Additionally, the ΔpdtaS mutant revealed lower activity of the respiratory chain as measured by the rate of TTC (triphenyltetrazolium chloride) reduction, while at the same time showing only insignificant changes in the uptake of aminoglycosides. We postulate that deficiency of PdtaS affects the oxidative respiration rates and ribosomal composition causing relevant changes to intrinsic resistance or susceptibility to antibiotics targeting ribosomes, which are commonly used to treat mycobacterial infections.

Minimum inhibitory concentration distributions for first- and second-line antimicrobials against Mycobacterium tuberculosis

We report the range of minimum inhibitory concentrations for six antimicrobial drugs in 228 clinical Mycobacterium tuberculosis (MTB) isolates from three distinct groups of patients (unselected patients, patients at high risk of drug-resistant TB and HIV-positive patients) in Lima, Peru. These data highlight the challenges of and discriminatory characteristics required for MTB drug susceptibility testing.

Screening of Fruits of Seven Plants Indicated for Medicinal Use in Iraq

Introduction:

Coumarins exert many biological effects in humans, animals, and plants, which make the evaluation of their biological activities and study of their role in ethnomedicine highly valued.

Objectives:

Here, we selected seven plants which have ethnopharmacological use as antimicrobial in Iraq and the aims were to quantify the two structural isomers bergapten and methoxsalen in their seeds, to evaluate the antibacterial activities against several clinical isolates, and to isolate bergapten and methoxsalen from Ammi majus.

Materials and Methods:

Seven plants were extracted by petroleum ether (PE) and ethanol (EtOH). Bergapten and methoxsalen were separated and purified by preparative thin-layer chromatography. Quantification of the furanocoumarins has been conducted by high-performance liquid chromatography, and all the plant extracts and pure compounds were checked for antibacterial activities utilizing alamar blue microplate assay.

Results:

Cuminum cyminum was deprived of bergapten and methoxsalen and methoxsalen was not detected from Apium graveolens. Bergapten was abundant in PE more than in EtOH; on the other hand, EtOH was rich in methoxsalen. The separation of the two structural isomers was performed using normal phase chromatography and ultraviolet light as an indicator. All extracts showed weak to moderate antibacterial activities against Gram-positive isolates which were more sensitive than the negative ones. C. cyminum extract was least active, uncover the antibacterial role of bergapten and methoxsalen.

Conclusion:

These findings support the medicinal use of seeds of seven plants from Apiaceae family and quantify the two pharmacologically important furanocoumarins (bergapten and methoxsalen).

SUMMARY

This study was conducted to evaluate the antibacterial activities of seven plants seeds used in local medicine in Iraq. High-performance liquid chromatography was used to quantify bergapten and xanthotoxin in non-polar and polar extracts of these seeds. This study supports the medicinal use of these plants and clarifies the role of bergapten and xanthotoxin in antibacterial activities of these plants.

Abbreviations used: EtOH: Ethanol; MIC: Minimum inhibitory concentration; PE: Petroleum ether; Rf: Retardation factor; Rt: Retention time.

Detection of pyrazinamide resistance of Mycobacterium tuberculosis using nicotinamide as a surrogate

OBJECTIVES

Despite the importance of pyrazinamide (PZA) in tuberculosis treatment, PZA susceptibility testing is not routinely performed because of its acid pH requirement. We evaluated the Microplate Alamar Blue assay (MABA) to detect resistance to PZA using nicotinamide (NIC) as a surrogate in neutral pH and identify the appropriate cutoff point for the assay.

METHODS

The NIC minimal inhibition concentrations (MICs) for 125 Mycobacterium tuberculosis clinical isolates were tested by MABA at nine different concentrations (8-2000 μg/mL). The PZA susceptibility testing by the BACTEC MGIT 960 system was used as a reference method. The pncA gene and its promoter region were sequenced for all the recruited strains.

RESULTS

A total of 64 of 125 clinical isolates were identified as resistant by MGIT 960. Using a minimum inhibitory concentration (MIC) of >500 μg/mL as the cutoff concentration to define resistance presented the best fit of the MABA assay with the MGIT 960 outcomes. MABA demonstrated sensitivity of 100% (95% confidence interval, 92.6-100), specificity of 95.2% (95% confidence interval, 86.0-98.8) and an accuracy of 97.6% compared to the MGIT 960 method. Nine PZA susceptible strains defined by MGIT 960 also had pncA mutations; however, three of them were defined as PZA resistant by NIC MABA with MIC ≥2000 μg/mL.

CONCLUSIONS

The NIC substitution method for PZA susceptibility test is reliable, cheap, rapid and easy, which makes it promising for use in clinical laboratories.

Susceptibility profiles of Nocardia spp. to antimicrobial and antituberculotic agents detected by a microplate Alamar Blue assay

Nocardia species are ubiquitous in natural environments and can cause nocardiosis. Trimethoprim-sulfamethoxazole has long been the monotherapy treatment of choice, but resistance to this treatment has recently emerged. In this study, we used microplate Alamar Blue assays to determine the antimicrobial susceptibility patterns of 65 standard Nocardia isolates, including 28 type strains and 20 clinical Nocardia isolates, to 32 antimicrobial agents, including 13 little studied drugs. Susceptibility to the most commonly used drug, trimethoprim-sulfamethoxazole, was observed in 98% of the isolates. Linezolid, meropenem, and amikacin were also highly effective, with 98%, 95%, and 90% susceptibility, respectively, among the isolates. The isolates showed a high percentage of resistance or nonsusceptibility to isoniazid, rifampicin, and ethambutol. For the remaining antimicrobials, resistance was species-specific among isolates and was observed in traditional drug pattern types. In addition, the antimicrobial susceptibility profiles of a variety of rarely encountered standard Nocardia species are reported, as are the results for rarely reported clinical antibiotics. We also provide a timely update of antimicrobial susceptibility patterns that includes three new drug pattern types. The data from this study provide information on antimicrobial activity against specific Nocardia species and yield important clues for the optimization of species-specific Nocardia therapies.

Rational design and synthesis of novel diphenyl ether derivatives as antitubercular agents

A series of triclosan mimic diphenyl ether derivatives have been synthesized and evaluated for their in vitro antitubercular activity against Mycobacterium tuberculosis H37Rv. The binding mode of the compounds at the active site of enoyl-acyl carrier protein reductase of M. tuberculosis has been explored. Among them, compound 10b was found to possess antitubercular activity (minimum inhibitory concentration =12.5 µg/mL) comparable to triclosan. All the synthesized compounds exhibited low levels of cytotoxicity against Vero and HepG2 cell lines, and three compounds 10a, 10b, and 10c had a selectivity index more than 10. Compound 10b was also evaluated for log P, pKa, human liver microsomal stability, and % protein binding, in order to probe its druglikeness. Based on the antitubercular activity and druglikeness profile, it may be concluded that compound 10b could be a lead for future development of antitubercular drugs.

S. S, Kulkarni M. Design, synthesis and evaluation of diphenyl ether analogues as antitubercular agents

We herein report the investigation of new diphenyl ethers asMycobacterium tuberculosisenoyl-acyl carrier protein reductase (InhA) inhibitors by structure-based drug design approach.

Identification of Novel Inhibitors of Mycobacterium tuberculosis PknG Using Pharmacophore Based Virtual Screening, Docking, Molecular Dynamics Simulation, and Their Biological Evaluation

PknG is a Ser/thr protein kinase that plays a crucial role in regulatory processes within the mycobacterial cell and signaling cascade of the infected host cell. The essentiality of PknG in mycobacterial virulence by blocking phagosome-lysosome fusion as well as its role in intrinsic antibiotic resistance makes it an attractive drug target. However, only very few compounds have been reported as Mycobacterium tuberculosis PknG (MtPknG) inhibitors so far. Therefore, in an effort to find potential inhibitors against MtPknG, we report here a sequential pharmacophore-based virtual screening workflow, 3-fold docking with different search algorithms, and molecular dynamic simulations for better insight into the predicted binding mode of identified hits. After detailed analysis of the results, six ligands were selected for in vitro analysis. Three of these molecules showed significant inhibitory activity against MtPknG. In addition, inhibitory studies of mycobacterial growth in infected THP-1 macrophages demonstrated considerable growth inhibition of M. bovis BCG induced through compound NRB04248 without any cytotoxic effect against host macrophages. Our results suggest that the compound NRB04248 can be explored for further design and optimization of MtPknG inhibitors.

Efflux pump gene expression in multidrug-resistant Mycobacterium tuberculosis clinical isolates

Isoniazid (INH) and rifampicin (RIF) are the two most effective drugs in tuberculosis therapy. Understanding the molecular mechanisms of resistance to these two drugs is essential to quickly diagnose multidrug-resistant (MDR) tuberculosis and extensive drug-resistant tuberculosis. Nine clinical Mycobacterium tuberculosis isolates resistant to only INH and RIF and 10 clinical pan-sensitive isolates were included to evaluate the expression of 20 putative drug efflux pump genes and sequence mutations in rpoB (RIF), katG (INH), the inhA promoter (INH), and oxyR-ahpC (INH). Nine and three MDR isolates were induced to overexpress efflux pump genes by INH and RIF, respectively. Eight and two efflux pump genes were induced to overexpress by INH and RIF in MDR isolates, respectively. drrA, drrB, efpA, jefA (Rv2459), mmr, Rv0849, Rv1634, and Rv1250 were overexpressed under INH or RIF stress. Most efflux pump genes were overexpressed under INH stress in a MDR isolates that carried the wild-type katG, inhA, and oxyR-ahpC associated with INH resistance than in those that carried mutations. The expression levels of 11 genes (efpA, Rv0849, Rv1250, P55 (Rv1410c), Rv1634, Rv2994, stp, Rv2459, pstB, drrA, and drrB) without drug inducement were significantly higher (P < 0.05) in nine MDR isolates than in 10 pan-sensitive isolates. In conclusion, efflux pumps may play an important role in INH acquired resistance in MDR M. tuberculosis, especially in those strains having no mutations in genes associated with INH resistance; basal expression levels of some efflux pump genes are higher in MDR isolates than in pan-sensitive isolates and the basal expressional differences may be helpful to diagnose and treat resistant tuberculosis.

Study of efflux pump gene expression in rifampicin-monoresistant Mycobacterium tuberculosis clinical isolates

Rifampicin (RIF) resistance is a risk factor for poor outcome in tuberculosis (TB). In Mycobacterium tuberculosis, both target gene mutation and efflux pumps have major roles in the resistance to anti-TB drugs. This study aimed to determine whether RIF induces efflux pump activation in RIF-monoresistant M. tuberculosis strains. Here, we took advantage of 16 RIF-monoresistant M. tuberculosis clinical isolates to evaluate the expression of 27 putative drug efflux pump genes and measured the influence of four drug efflux pump inhibitors, carbonyl cyanide m-chlorophenyl hydrazone (CCCP), verapamil (VP), thioridazine (TZ) and chlorpromazine (CPZ), on the RIF MICs of these strains. Eight of the 16 RIF-monoresistant isolates carried mutations in rpoB and overexpressed one or two of the following putative efflux pump genes: Rv2333, drrB, drrC, Rv0842, bacA and efpA. CCCP, VP, TZ and CPZ lowered the RIF MICs greater than fourfold in 6, 12, 9 and 12 isolates, respectively. The lowered RIF MICs by VP and CPZ were identical and stronger than CCCP (P-values were all 0.033). In conclusion, the efflux pumps Rv2333, DrrB, DrrC, Rv0842, BacA and EfpA may have a role in RIF resistance in addition to classical mutations in the rpoB gene, and the addition of VP and CPZ could significantly increase RIF susceptibility in RIF-monoresistant M. tuberculosis.

Design of Novel Mycobacterium tuberculosis Pantothenate Synthetase Inhibitors: Virtual Screening, Synthesis and In Vitro Biological Activities

Pantothenate synthetase (PS) enzyme involved in the pantothenate biosynthetic pathway is essential for the virulence and persistent growth of Mycobacterium tuberculosis (MTB). It is encoded by the panC gene, and has become an appropriate target for developing new therapeutics for tuberculosis. Here we report new inhibitors active against MTB PS developed using energy based pharmacophore modelling of the available proteininhibitor complex (3IVX) and virtual screening of a large commercial library. The e-pharmacophore model consisted of a ring aromatic (R), negative ionizable (N) and acceptor (A) sites. Compounds 5 and 10 emerged as promising hits with IC50 s 2.18 µM and 6.63 µM respectively. Further structural optimization was attempted to optimize lead 10 using medicinal chemistry approach and six compounds were found to exhibit better enzyme inhibition compared to parent compound lead 10 (<6 µM).

Antimicrobial susceptibility of standard strains of nontuberculous mycobacteria by microplate Alamar Blue assay

In this study, 24 standard nontuberculous mycobacteria (NTM) species strains including 12 slowly growing mycobacteria strains and 12 rapidly growing mycobacteria strains were subjected to drug susceptibility testing using microplate Alamar Blue assay-based 7H9 broth. The most active antimicrobial agents against the 24 NTM strains were streptomycin, amikacin, the fluoroquinolones, and the tetracyclines. Mycobacterium chelonae, Mycobacterium abscessus, Mycobacterium bolletii, and Mycobacterium simiae are resistant to most antimicrobial agents. The susceptibility results of this study from 24 NTM standard strains can be referenced by clinicians before susceptibility testing for clinical isolates is performed or when conditions do not allow for susceptibility testing. The application of broth-based methods is recommended by the Clinical and Laboratory Standards Institute, and the documentation of the susceptibility patterns of standard strains of mycobacteria can improve the international standardization of susceptibility testing methods.

Measuring of Mycobacterium tuberculosis growth. A correlation of the optical measurements with colony forming units

The quantification of colony forming units (cfu), turbidity, and optical density at 600 nm (OD₆₀₀) measurements were used to evaluate Mycobacterium tuberculosis growth. Turbidity and OD₆₀₀ measurements displayed similar growth curves, while cfu quantification showed a continuous growth curve. We determined the cfu equivalents to McFarland and OD₆₀₀ units.

Diagnostic accuracy and reproducibility of WHO-endorsed phenotypic drug susceptibility testing methods for first-line and second-line antituberculosis drugs

In an effort to update and clarify policies on tuberculosis drug susceptibility testing (DST), the World Health Organization (WHO) commissioned a systematic review evaluating WHO-endorsed diagnostic tests. We report the results of this systematic review and meta-analysis of the diagnostic accuracy and reproducibility of phenotypic DST for first-line and second-line antituberculosis drugs. This review provides support for recommended critical concentrations for isoniazid and rifampin in commercial broth-based systems. Further studies are needed to evaluate critical concentrations for ethambutol and streptomycin that accurately detect susceptibility to these drugs. Evidence is limited on the performance of DST for pyrazinamide and second-line drugs.

A rapid, high-throughput viability assay for Blastocystis spp. reveals metronidazole resistance and extensive subtype-dependent variations in drug susceptibilities

Blastocystis is an emerging protistan parasite of controversial pathogenesis. Although metronidazole (Mz) is standard therapy for Blastocystis infections, there have been accumulating reports of treatment failure, suggesting the existence of drug-resistant isolates. Furthermore, very little is known about Blastocystis susceptibility to standard antimicrobials. In the present study, we established resazurin and XTT viability microassays for Blastocystis spp. belonging to subtypes 4 and 7, both of which have been suggested to represent pathogenic zoonotic subtypes. The optimized resazurin assay was used to screen a total of 19 compounds against both subtypes. Interestingly, subtype 7 parasites were resistant to Mz, a 1-position-substituted 5-nitroimidazole (5-NI), while subtype 4 parasites were sensitive. Some cross-resistance was observed to tinidazole, another 1-position 5-NI. Conversely, subtype 4 parasites were resistant to emetine, while subtype 7 parasites were sensitive. Position 2 5-NIs were effective against both subtypes, as were ornidazole, nitazoxanide, furazolidone, mefloquine, quinicrine, quinine, cotrimoxazole (trimethoprim-sulfamethoxazole), and iodoacetamide. Both subtypes were resistant to chloroquine, doxycycline, paromomycin, ampicillin, and pyrimethamine. This is the first study to report extensive variations in drug sensitivities among two clinically important subtypes. Our study highlights the need to reevaluate established treatment regimens for Blastocystis infections and offers clear new treatment options for Mz treatment failures.

Rapid methods for testing inhibitors of mycobacterial growth

Considering the increased concerns with controlling infectious epidemics such as tuberculosis, a global concerted effort (WHO) is now dead-lined to tackle the emergence of extensive drug resistance through identifying a novel line of therapeutics which will on the one hand shorten the course of treatment and on the other is also expected to be effective against the emerging resistant strains. Major problems with the preclinical drug screening against the uniquely slow-growing pathogen Mycobacterium tuberculosis are either found expensive, time-consuming, or require a highly complex laboratory setup. A rapid and convenient, although relatively inexpensive, method requiring very little consumption of inhibitors within a simple microbiology setup for antimycobacterial screening is thus timely. The spot-culture growth inhibition assay aims to test the biological activity of a number of newly discovered natural products and thousands of novel chemicals synthesized on the basis of basic structural and molecular biology studies. Many different classes of novel chemical entities are now independently prepared around the world by distinguished chemists on the chemical behavior of the group of molecules. To serve the purpose of antimycobacterials screening, we aim to describe a method in this chapter performed in a six-well plate format. This method can also be extended accurately to a 96-well plate format according to the necessity of the project. In addition to evaluating a range of prospective drug candidates, this method would also contribute to elucidate substrates for many putative endogenous pathways through comparing the chemical inhibition with the corresponding genetic modification.

Optimization of a rapid viability assay for Mycobacterium avium subsp. paratuberculosis by using alamarBlue

A microtiter alamarBlue assay was adapted and optimized for Mycobacterium avium subsp. paratuberculosis. Using cell concentrations ranging from 10(4) to 10(8) CFU/ml, a minimum incubation time to indicate viability was obtained after 24 h. Rifampin (rifampicin) was used to demonstrate that this method has applications for high-throughput screening against M. avium subsp. paratuberculosis.