Biology subjects

Shi, W.

Publications and source records attributed to Shi, W..

211 records · Page 12Linked to original sources

bioRxiv2018

Mutations in efflux pump Rv1258c (Tap) cause resistance to pyrazinamide and other drugs in M. tuberculosis

Although drug resistance in M. tuberculosis is mainly caused by mutations in drug activating enzymes or drug targets, there is increasing interest in possible role of efflux in causing drug resistance. Previously, efflux genes are shown upregulated upon drug exposure or implicated in drug resistance in overexpression studies, but the role of mutations in efflux pumps identified in clinical isolates in causing drug resistance is unknown. Here we investigated the role of mutations in efflux pump Rv1258c (Tap) from clinical isolates in causing drug resistance in M. tuberculosis by constructing point mutations V219A, S292L in Rv1258c in the chromosome of M. tuberculosis and assessed drug susceptibility of the constructed mutants. Interestingly, V219A, S292L point mutations caused clinically relevant drug resistance to pyrazinamide (PZA), isoniazid (INH), and streptomycin (SM), but not to other drugs in M. tuberculosis. While V219A point mutation conferred a low level resistance, the S292L mutation caused a higher level of resistance. Efflux inhibitor piperine inhibited INH and PZA resistance in the S292L mutant but not in the V219A mutant. S292L mutant had higher efflux activity for pyrazinoic acid (the active form of PZA) than the parent strain. We conclude that point mutations in the efflux pump Rv1258c in clinical isolates can confer clinically relevant drug resistance including PZA and could explain some previously unaccounted drug resistance in clinical strains. Future studies need to take efflux mutations into consideration for improved detection of drug resistance in M. tuberculosis and address their role in affecting treatment outcome in vivo.

microbiology↗

bioRxiv2018

Identification of novel mutations in LprG (rv1411c), rv0521, rv3630, rv0010c, ppsC, cyp128 associated with pyrazinoic acid/pyrazinamide resistance in Mycobacterium tuberculosis

There is currently considerable interest in understanding the mechanisms of action of pyrazinamide (PZA), a critical frontline tuberculosis (TB) drug that plays a unique role in shortening TB therapy due to its unique activity against Mycobacterium tuberculosis persisters that are not killed by other TB drugs.1,2 Despite the importance of PZA in the treatment of both drug susceptible and drug-resistant TB and its simple structure, its mechanisms of action are complex and are not well understood.1,2 PZA is a prodrug that is converted to the active form pyrazinoic acid (POA) by nicotinamidase/pyrazinamidase (PZase) encoded by the pncA gene,3 whose mutation is the most common mechanism of PZA resistance in M. tuberculosis.3-5 However, some low level PZA-resistant strains (MIC=200-300 g/ml, pH6.0) do not have mutations in the pncA gene.5,6 Recent studies have identified rpsA, which encodes the ribosomal protein S1 involved in both translation and trans-translation process, as a target of PZA,7 where its mutations are associated with PZA resistance from clinical isolates. In addition, mutations in panD encoding aspartate decarboxylase were identified as a new mechanism of PZA resistance from in vitro mutants resistant to PZA and the PanD protein was found to be another target of PZA.8,9 panD mutations were initially found in mutants resistant to PZA 8 and then in mutants resistant to POA. 9,10 It is worth noting that previously POA-resistant mutants could not be isolated at acid pH which is required for higher activity of PZA against M. tuberculosis. However, we were able to successfully isolate POA-resistant mutants with high POA concentrations at close to neutral pH (pH 6.8),9 which led to discovery of new genes involved in POA and PZA resistance. For example, clpC1, which was also isolated from mutants resistant to PZA,11 was identified in mutants resistant to POA.12

microbiology↗

bioRxiv2017

Clofazimine targets essential nucleoid associated protein, mycobacterial integration host factor (mIHF), in Mycobacterium tuberculosis

Clofazimine (CFZ) is a phenazine derivative used for treatment of leprosy, MDR-TB and XDR-TB. There is recent interest in understanding how CFZ works following the demonstration of its unique ability to shorten the treatment of MDR-TB. However, the target of CFZ in mycobacteria has remained elusive. Here, we show that CFZ binds to mycobacterial integration host factor (mIHF), which is an essential nucleoid associated protein in mycobacteria involved in DNA protection, chromosome organization and global gene regulation. We demonstrate that CFZ inhibits mIHF binding to DNA and interferes with mycobacterial gene expression. This mode of action is unique among all antibiotics including antimycibacterial agents and may help to explain its unusual action against Mycobacterium tuberculosis. Our study provides new insight about the mechanism of action of this intriguing drug and has implications for developing more effective treatment of TB.

microbiology↗

bioRxiv2017

A high-throughput analysis method of microdroplet PCR coupled with fluorescence spectrophotometry

Here we report a novel microdroplet PCR method combined with fluorescence spectrophotometry (MPFS), which allows for qualitative, quantitative and high -throughput detection of multiple DNA targets. In this study, each pair of primers was labeled with a specific fluorophore. Through microdroplet PCR, a target DNA was amplified and labeled with the same fluorophore. After products purification, the DNA products tagged with different fluorophores could be analyzed qualitatively by the fluorescent intensity determination. The relative fluorensence unit was also measured to construct the standard curve and to achieve quantitative analysis. In a reaction, the co -amplified products with different fluorophores could be simultaneously analyzed to achieve high -throughput detection. We used four kinds of GM maize as a model to confirm this theory. The qualitative results revealed high specificity and sensitivity of 0.5% (w / w). The quantitative results revealed that the limit of detection was 103copies and with good repeatability. Moreover, reproducibility assay were further performed using four foodborne pathogenic bacteria. Consequently, the same qualitative, quantitative and high-throughput results were confirmed as the four GM maize.

biochemistry↗

bioRxiv2017

Serial Crystallography with Multi-stage Merging of 1000’s of Images

KAMO and Blend provide particularly effective tools to manage automatically the merging of large numbers of datasets from serial crystallography. The requirement for manual intervention in the process can be reduced by extending Blend to support additional clustering options such as use of more accurate cell distance metrics and use of reflection-intensity correlation coefficients to infer "distances" among sets of reflec- tions. This increases the sensitivity to differences in unit cell parameters and allows for clustering to assemble nearly complete datasets on the basis of intensity or ampli- tude differences. If datasets are already sufficiently complete to permit it, one applies KAMO once and clusters the data using intensities only. If starting from incomplete datasets, one applies KAMO twice, first using cell parameters. In this step we use either the simple cell vector distance of the original Blend, or we use the more sensi- tive NCDist. This step tends to find clusters of sufficient size so that, when merged, each cluster is sufficiently complete to allow reflection intensities or amplitudes to be compared. One then uses KAMO again using the correlation between the reflections having a common hkl to merge clusters in a way sensitive to structural differences that may not have perturbed the cell parameters sufficiently to make meaningful clusters. Many groups have developed effective clustering algorithms that use a measurable physical parameter from each diffraction still or wedge to cluster the data into cate- gories which then can be merged, one hopes, to yield the electron density from a single protein form. Since these physical parameters are often largely independent from one another, it should be possible to greatly improve the efficacy of data clustering software by using a multi-stage partitioning strategy. Here, we have demonstrated one possible approach to multi-stage data clustering. Our strategy is to use unit-cell clustering until merged data is sufficiently complete then to use intensity-based clustering. We have demonstrated that, using this strategy, we are able to accurately cluster datasets from crystals that have subtle differences.

bioinformatics↗

bioRxiv2017

On growth and form of the distal air exchange surfaces within the lung.

Herein we show, using several novel imaging and computational approaches, how the air exchange units (AEUs) of the lung develop from the tips and sides of distinct families of tortuous ducts, that themselves ramify as distinct families distal to the bronchoalveolar duct junctions (BADJs), prenatally in humans but postnatally in mice. The mature AEUs thus consist of indented spheroids tightly packed between quite regularly spaced distal ducts. Since the diameter of the BADJs and the distal ducts increases rather than decreasing during the formation of AEUs, we further deduce that the AEUs must form by circular epithelial precursor buckling at their mouths with resulting extrusion of their lumen into the surrounding mesenchyme, stabilized firstly by interlocking rings of elastin and later by rings of elastin and collagen fibers surrounding the mouth of each of the prospective AEUs. Furthermore, we show that the surface of each of the AEUs is highly rugose, being indented by the capillary network that lies close beneath the AES membranes. We propose that, the kissing theorem proposed of Newton that expresses the number of times billiard balls may touch within their frame is a parsimonious solution to achieving optimum packing of the distal AES unit spaces, while allowing sufficient space between them to allow for conducting airways, closely applied pulsatile capillary blood vessels, lymphatics, nerves and other key components of the interstitial mesenchyme.\n\nSummary statementEmploying novel imaging and computational approaches we here deduce some new concepts as to how the distal shaping of airway lineage stem and progenitor cells may contribute to the growth and form of the air exchange surface (AES) of the lung, distal to the bronchoalveolar duct junction (BADJ). We then propose that the AES extrudes from the sides and tips of distinct families of small ducts, apparently by buckling of the thinning luminal epithelium into the surrounding mesenchyme, stabilized firstly by rings of elastin and later by rings of collagen and elastin fibers, that surround the mouth of each distal unit of the AES. We propose this mechanism as a parsimonious solution to achieving the optimum form, packing density and functional efficiency of the AES, while allowing sufficient space between for the plumbing of conducting airways, pulsatile capillary blood vessels, lymphatics, nerves and other key matrix and cellular components within the interstitial mesenchyme.

developmental biology↗

bioRxiv2017

High Activity Of Selective Essential Oils Against Stationary Phase Borrelia burgdorferi As A Persister Model

Although the majority of patients with Lyme disease can be cured with the standard 2-4 week antibiotic treatment, about 10-20% of patients continue to suffer from post-treatment Lyme disease syndrome (PTLDS). While the cause for this is debated, one possibility is due to persisters not killed by the current Lyme antibiotics. It has been reported that essential oils have antimicrobial activities and some have been used by patients with persisting Lyme disease symptoms. However, the activity of essential oils against the causative agent Borrelia burgdorferi (B. burgdorferi) has not been carefully studied. Here, we evaluated the activity of 34 essential oils against B. burgdorferi stationary phase culture as a model for persisters. We found that many essential oils had varying degrees of activity against B. burgdorferi, with top 5 essential oils (oregano, cinnamon bark, clove bud, citronella, and wintergreen) at a low concentration of 0.25% showing more activity than the persister drug daptomycin. Interestingly, some highly active essential oils were found to have excellent anti-biofilm ability as shown by their ability to dissolve the aggregated biofilm-like structures. The top 3 hits, oregano, cinnamon bark and clove bud, completely eradicated all viable cells without regrowth in subculture. Carvacrol was found to be the most active ingredient of oregano oil showing excellent activity against B. burgdorferi stationary phase cells, while p-cymene and -terpinene had no apparent activity. Future studies are needed to characterize and optimize the active essential oils in drug combinations in vitro and in vivo for improved treatment of persistent Lyme disease.\n\nIMPORTANCEThere is a huge need for effective treatment of patients with Lyme disease who suffer from PTLDS. Recent in vitro and in vivo studies suggest that B. burgdorferi develops persisters that are not killed by the current Lyme antibiotics as a possible contributor to this condition. Although essential oils are used by patients with Lyme disease with variable improvement in symptoms, their anti-borrelia activity has not been carefully studied. Here we found that not all essential oils have adequate anti-borrelia activity and identified some highly potent essential oils (oregano, cinnamon bark, clove bud) that have even higher anti-persister and anti-biofilm activity than the persister drug daptomycin. Carvacrol was found to be the most active ingredient of oregano oil and have the potential to serve as a promising oral persister drug. Our findings may have implications for developing improved treatment of persisting Lyme disease.

microbiology↗

bioRxiv2017

On Growth And Form Of The Distal Air Exchange Surfaces Within The Lung

Summary statementEmploying novel imaging and computational approaches we here deduce some new concepts as to how the distal shaping of airway lineage stem and progenitor cells may contribute to the growth and form of the air exchange surface (AES) of the lung, distal to the bronchoalveolar duct junction (BADJ). We then propose that the AES extrudes from the sides and tips of distinct families of small ducts, apparently by buckling of the thinning luminal epithelium into the surrounding mesenchyme, stabilized firstly by rings of elastin and later by rings of collagen and elastin fibers, that surround the mouth of each distal unit of the AES. We propose this mechanism as a parsimonious solution to achieving the optimum form, packing density and functional efficiency of the AES, while allowing sufficient space between for the plumbing of conducting airways, pulsatile capillary blood vessels, lymphatics, nerves and other key matrix and cellular components within the interstitial mesenchyme.\n\nAbstractHerein we show, using several novel imaging and computational approaches, how the air exchange units (AEUs) of the lung develop from the tips and sides of distinct families of tortuous ducts, that themselves ramify as distinct families distal to the bronchoalveolar duct junctions (BADJs), prenatally in humans but postnatally in mice. The mature AEUs thus consist of indented spheroids tightly packed between quite regularly spaced distal ducts. Since the diameter of the BADJs and the distal ducts increases rather than decreasing during the formation of AEUs, we further deduce that the AEUs must form by circular epithelial precursor buckling at their mouths with reulsting extrusion of their lumen into the surrounding mesenchyme, stabilized firstly by interlocking rings of elastin and later by rings of elastin and collagen fibers surrounding the mouth of each of the prospective AEUs. Furthermore, we show that the surface of each of the AEUs is highly rugose, being indented by the capillary network that lies close beneath the AES membranes. We propose that, the kissing theorem proposed of Newton tha expresses the number of times billiard balls may touch within their frame is a parsimonious solution to achieving optimum packing of the distal AES unit spaces, while allowing sufficient space between them to allow for conducting airways, closely applied pulsatile capillary blood vessels, lymphatics, nerves and other key components of the interstitial mesenchyme.

developmental biology↗

bioRxiv2017

Identification of a Novel Gene argJ involved in Arginine Biosynthesis Critical for Persister Formation in Staphylococcus aureus

Staphylococcus aureus can cause both acute and recurrent persistent infections such as peritonitis, endocarditis, abscess, osteomyelitis, and chronic wound infections. An effective treatment to eradicate the persistent disease is still lacking as the mechanisms of S. aureus persistence are poorly understood. In this study, we performed a comprehensive and unbiased high-throughput mutant screen using S. aureus USA300 and identified argJ, encoding an acetyltransferase in the arginine biosynthesis pathway, whose mutation produced a significant defect in persister formation in multiple drugs and stresses. Genetic complementation and arginine supplementation restored persistence in the ArgJ mutant. Quantitative real-time PCR analysis showed that the arg genes were over-expressed under drug stressed conditions and in stationary phase cultures. In addition, the ArgJ mutant had attenuated virulence in both C. elegans and mouse models of infection. Our studies identify a novel mechanism of persistence mediated by arginine metabolism in S. aureus. These findings will not only provide new insights about the mechanisms of S. aureus persistence but also offer novel therapeutic targets that may help to develop more effective treatment of persistent S. aureus infections.

microbiology↗

bioRxiv2017

Varying Effects of Common Tuberculosis Drugs on Enhancing Clofazimine Activity in vitro

Clofazimine (CFZ), originally developed as an anti-tuberculosis (TB) drug in the 1950s 1, is commonly used to treat leprosy and also nontuberculous mycobacterial (NTM) infections. 2 Although CFZ has good activity against Mycobacterium tuberculosis, it was not used in the treatment of pulmonary TB mainly because it had the side effect of skin discoloration and there were other more effective drugs like isoniazid (INH), rifampin (RIF) and pyrazinamide (PZA) already available for the treatment of TB. 2 However, the increasing emergence of multi-drug-resistant TB (MDR-TB) has revived interest in the use of CFZ to treat MDR-TB. 2,3\n\nAlthough resistance to CFZ has been shown to be mediated by mutations in Rv0678,4,5 Rv1979c, or Rv2535c (PepQ),5 the mode of action of CFZ has remained poorly understood. CFZ appears to hav ...

microbiology↗

bioRxiv2017

Identification of novel mutations associated with cycloserine resistance in Mycobacterium tuberculosis

ObjectivesD-cycloserine (DCS) is an important second-line drug used to treat multi-drug resistant (MDR) and extensively drug-resistant (XDR) tuberculosis. However, the mechanisms of resistance to DCS are not well understood. Here we investigated the molecular basis of DCS resistance using in vitro isolated resistant mutants of Mycobacterium tuberculosis.\n\nMethodsM. tuberculosis H37Rv was subjected to mutant selection on 7H11 agar plates containing varying concentrations of DCS. A total of 35 DCS-resistant mutants were isolated and 18 mutants were subjected to whole genome sequencing. The identified mutations associated with DCS resistance were confirmed by PCR-Sanger sequencing.\n\nResultsWe identified mutations in 17 genes that are associated with DCS resistance. Except mutations in alr (rv3423c) which is known to be involved in DCS resistance, 16 new genes rv0059, betP (rv0917), rv0221, rv1403c, rv1683, rv1726, gabD2 (rv1731), rv2749, sugI (rv3331), hisC2 (rv3 772), single mutation in 5 intergenic region of rv3345c and rv1435c, and insertion in 3 region of rv0759c were identified as solo mutations in their respective DCS-resistant mutants. Our findings indicate that the mechanisms of DCS resistance are more complex than previously thought and involve genes participating in different cellular functions such as lipid metabolism, methyltransferase, stress response, and transport proteins.\n\nConclusionsNew mutations in diverse genes associated with DCS are identified, which shed new light on the mechanisms of action and resistance of DCS. Future studies are needed to verify these findings in clinical strains so that molecular detection of DCS resistance for improved treatment of MDR-TB can be developed.

microbiology↗

bioRxiv2017

Identification of drug candidates that enhance pyrazinamide activity from a clinical drug library

Tuberculosis (TB) remains a leading cause of morbidity and mortality globally despite the availability of the TB therapy. 1 The current TB therapy is lengthy and suboptimal, requiring a treatment time of at least 6 months for drug susceptible TB and 9-12 months (shorter Bangladesh regimen) or 18-24 months (regular regimen) for multi-drug-resistant tuberculosis (MDR-TB). 1 The lengthy therapy makes patient compliance difficult, which frequently leads to emergence of drug-resistant strains. The requirement for the prolonged treatment is thought to be due to dormant persister bacteria which are not effectively killed by the current TB drugs, except rifampin and pyrazinamide (PZA) which have higher activity against persisters. 2, 3 Therefore new therapies should address the problem of insufficient efficacy against M. tuberculosis persisters, which could cause relapse of clinical disease. 4 PZA is a critical frontline TB drug that kills persister bacteria 5 and shortens the TB treatment from 9-12 months to 6 months. 6, 7 Although several new TB drugs are showing promise in clinical studies, none can replace PZA as they all have to be used together with PZA. 7 Because of the essentiality of PZA and the high cost of developing new drugs, in this study, we explored the idea of identifying drugs that enhance the anti-persister activity of PZA as an economic alternative approach to developing new drugs for improved treatment by screening an clinical drug library against old M. tuberculosis cultures enriched with persisters.

microbiology↗

bioRxiv2017

Activity of Sulfa Drugs and Their Combinations against Stationary Phase B. burgdorferi in vitro

Lyme disease is a most common vector borne disease in the US. Although the majority of Lyme patients can be cured with the standard 2-4 week antibiotic treatment, at least 10-20% of patients continue to suffer from prolonged post-treatment Lyme disease syndrome (PTLDS). While the cause for this is unclear, one possibility is that persisting organisms are not killed by current Lyme antibiotics. In our previous studies, we screened an FDA drug library and an NCI compound library on B. burgdorferi and found some drug hits including sulfa drugs as having good activity against B. burgdorferi stationary phase cells. In this study, we evaluated the relative activity of three commonly used sulfa drugs sulfamethoxazole (Smx), dapsone (Dps), sulfachlorpyridazine (Scp), and also trimethoprim (Tmp), and assessed their combinations with the commonly prescribed Lyme antibiotics for activities against B. burgdorferi stationary phase cells. Using the same molarity concentration, dapsone, sulfachlorpyridazine and trimethoprim showed very similar activity against stationary phase B. burgdorferi enriched in persisters, however, sulfamethoxazole was the least active drug among the three sulfa drugs tested. Interestingly, contrary to other bacterial systems, Tmp did not show synergy in drug combinations with the three sulfa drugs at their clinically relevant serum concentrations against B. burgdorferi. We found that sulfa drugs combined with other antibiotics were more active than their respective single drugs and that four-drug combinations were more active than three-drug combinations. Four drug combinations dapsone+minocycline+cefuroxime+azithromycin and dapsone+minocycline+cefuroxime+rifampin showed best activity against stationary phase B. burgdorferi in these sulfa drug combinations. However, these 4-sulfa drug containing combinations still had considerably less activity against B. burgdorferi stationary phase cells than the daptomycin+cefuroxime+doxycycline used as a positive control which completely eradicated B. burgdorferi stationary phase cells. Future studies are needed to evaluate and optimize the sulfa drug combinations in vitro and also in animal models.

microbiology↗