Brucella-driven host N-glycome remodeling controls infection

Many powerful methods have been employed to elucidate the global transcriptomic, proteomic, or metabolic responses to pathogen-infected host cells. However, the host glycome responses to bacterial infection remain largely unexplored, and hence, our understanding of the molecular mechanisms by which bacterial pathogens manipulate the host glycome to favor infection remains incomplete. Here, we address this gap by performing a systematic analysis of the host glycome during infection by the bacterial pathogen Brucella spp. that cause brucellosis. We discover, surprisingly, that a Brucella effector protein (EP) Rhg1 induces global reprogramming of the host cell N-glycome by interacting with components of the oligosaccharide transferase complex that controls N-linked protein glycosylation, and Rhg1 regulates Brucella replication and tissue colonization in a mouse model of brucellosis, demonstrating that Brucella exploits the EP Rhg1 to reprogram the host N-glycome and promote bacterial intracellular parasitism, thereby providing a paradigm for bacterial control of host cell infection.

Molecular Editing Enhances Oxidation Resistance of Menaquinone-Targeting Antibiotics Lysocin E and WAP-8294A2

Lysocin E (1 a) and WAP-8294A2 (2 a) are peptidic natural products with 37- and 40-membered macrocycles, respectively. Compounds 1 a and 2 a have potent antibacterial activities against Gram-positive bacteria and share a unique mode of action. The electron-rich indole ring of d-Trp-10 of 1 a and 2 a interacts with the electron-deficient benzoquinone ring of menaquinone, which is a co-enzyme in the bacterial respiratory chain. Formation of the electron-donor-acceptor complex causes membrane disruption, leading to cell death. Despite the promising activities of 1 a and 2 a, the susceptibility of Trp-10 to oxidative degradation potentially deters the development of these compounds as antibacterial drugs. To address this issue, we replaced the indole ring with more oxidation-resistant aromatics having a similar shape and electron-rich character. Specifically, analogues with benzofuran (1 b/2 b), benzothiophene (1 c/2 c), and 1-naphthalene (1 d/2 d) rings were designed, and chemically prepared by full solid-phase total syntheses. Antibacterial assays of the six analogues revealed similar activities of 1 d/2 d and markedly reduced activities of 1 b/2 b and 1 c/2 c compared with 1 a/2 a. Equipotent 1 d and 2 d both showed high resistance to oxidation by peroxyl radicals. Hence, the present study demonstrates a new molecular editing strategy for conferring oxidation stability on natural products with pharmacologically useful functions.

Construction of Five Tryptophan Isomers and Application of the Isomers to Solid-Phase Total Syntheses of Lysocin E Derivatives

Tryptophan (Trp) plays a unique role in peptides and proteins as its indole ring possesses an electron-rich character and an N1-H hydrogen-bond donor. Because of its non-rotationally symmetric structure, synthetic alterations of the orientation of the indole ring would modulate the intrinsic structures and functions of peptides and proteins. Here we developed synthetic routes to the five Trp isomers in which the C3-substitution of the indole ring was changed to the C2/4/5/6/7-substitutions, and applied the five monomers to Fmoc-based solid-phase peptide synthesis. Specifically, the five monomers were prepared via Negishi cross-coupling reactions of C2/4/5/6/7-iodoindoles. To demonstrate the applicability of the monomers to the solid-phase synthesis, the five Trp isomers of macrocyclic antibiotic lysocin E were selected as target molecules and synthesized through peptide elongation, on-resin macrocyclization, and global deprotection. The Trp isomers displayed markedly weaker antibacterial activity than the parent natural product, revealing the biological importance of the precise three-dimensional shape of the original Trp residue of lysocin E. The present methods for the preparation and application of these five Trp isomers provide a new strategy for analyzing and modifying the specific functions of numerous Trp-containing peptides and proteins beyond this study.

Hybrid assembly using long reads resolves repeats and completes the genome sequence of a laboratory strain of Staphylococcus aureus subsp. Aureus RN4220

Staphylococcus aureus RN4220 has been extensively used by staphylococcal researchers as an intermediate strain for genetic manipulation due to its ability to accept foreign DNA. Despite its wide use in laboratories, its complete genome is not available. In this study, we used a hybrid genome assembly approach using minION long reads and Illumina short reads to sequence the complete genome of S. aureus RN4220. The comparative analysis of the annotated complete genome showed the presence of 39 genes fragmented in the previous assembly, many of which were located near the repeat regions. Using RNA-Seq reads, we showed that a higher number of reads could be mapped to the complete genome than the draft genome and the gene expression profile obtained using the complete genome also differs from that obtained from the draft genome. Furthermore, by comparative transcriptomic analysis, we showed the correlation between expression levels of staphyloxanthin biosynthetic genes and the production of yellow pigment. This study highlighted the importance of long reads in completing microbial genomes, especially those possessing repetitive elements.

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S. aureus RN4220 is used as an intermediate strain for genetic manipulation.

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We completed its genome and found 39 fragmented genes in previous genome assembly.

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RNA-Seq analysis improved mapping of the reads with the use of complete genome.

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Expression of staphyloxanthin biosynthetic genes was correlated with its production.

Transcriptome change of Staphylococcus aureus in infected mouse liver

We performed in vivo RNA-sequencing analysis of Staphylococcus aureus in infected mouse liver using the 2-step cell-crush method. We compared the transcriptome of S. aureus at 6, 24, and 48 h post-infection (h.p.i) in mice and in culture medium. Genes related to anaerobic respiration were highly upregulated at 24 and 48 h.p.i. The gene expression patterns of virulence factors differed depending on the type of toxin. For example, hemolysins, but not leukotoxins and serine proteases, were highly upregulated at 6 h.p.i. Gene expression of metal transporters, such as iron transporters, gradually increased at 24 and 48 h.p.i. We also analyzed the transcriptome of mouse liver infected with S. aureus. Hypoxia response genes were upregulated at 24 and 48 h.p.i., and immune response genes were upregulated from 6 h.p.i. These findings suggest that gene expression of S. aureus in the host changes in response to changes in the host environment, such as the oxygenation status or immune system attacks during infection.

An in vivo transcriptomic analysis of Staphylococcus aureus infection in mice provides further insight into how this pathogen responds to changes in the host environment over time.

Burden of tuberculosis and hepatitis co-infection among people living with HIV in Nepal: a systematic review and meta-analysis

People living with HIV (PLHIV) are prone to tuberculosis (TB) and hepatitis co-infections, which cause substantial burden on morbidity and mortality. However, data on the burden of HIV co-infection from a specific low- and middle-income country are limited. To address this gap in evidence, a meta-analysis of published literature and country surveillance report was conducted to estimate the burden of TB, hepatitis B (HBV) and hepatitis C (HCV) co-infection among PLHIV in Nepal. Twenty-three studies, including 5900 PLHIV, were included in the meta-analysis. The pooled prevalence of HIV-TB, HIV-HBV and HIV-HCV co-infection was 19% (95% CI, 10-28%), 3% (2-5%) and 19% (4-33%), respectively. Low CD4 cell count (pooled odds ratio [OR] 4.38, 95% CI 1.11-17.25), smoking (3.07, 1.48-6.37) and alcohol drinking (3.12, 1.52-6.43) were significantly correlated with HIV-TB co-infection. The odds of HCV co-infection was greater in PLHIV, who were male (5.39, 1.54-18.89) and drug users (166.26, 15.94-1734.44). PLHIV who were on antiretroviral therapy had a reduced risk of HCV co-infection (0.49, 0.36-0.66) than the general PLHIV population. The burden of TB and hepatitis co-infection among PLHIV in Nepal was high. Regular screening of PLHIV for co-infections and prompt initiation of treatment are essential to reduce the transmission of infection and improve quality of life.

YjbH regulates virulence genes expression and oxidative stress resistance in Staphylococcus aureus

We previously reported that disruption of the yjbI gene reduced virulence of Staphylococcus aureus. In this study, we found virulence in both silkworms and mice was restored by introducing the yjbH gene but not the yjbI gene to both yjbI and yjbH genes-disrupted mutants, suggesting that yjbH, the gene downstream to the yjbI gene in a two-gene operon-yjbIH, is responsible for this phenomenon. We further observed a decrease in various surface-associated proteins and changes in cell envelope glycostructures in the mutants. RNA-seq analysis revealed that disruption of the yjbI and the yjbH genes resulted in differential expression of a broad range of genes, notably, significant downregulation of genes involved in virulence and oxidative stress. Administration of N-acetyl-L-cysteine, a free-radical scavenger, restored the virulence in both the mutants. Our findings suggested that YjbH plays a role in staphylococcal pathogenicity by regulating virulence gene expression, affecting the bacterial surface structure, and conferring resistance to oxidative stress in a host.

Serum apolipoprotein A-I potentiates the therapeutic efficacy of lysocin E against Staphylococcus aureus

Lysocin E is a lipopeptide with antibiotic activity against methicillin-resistant Staphylococcus aureus. For unclear reasons, the antibacterial activity of lysocin E in a mouse systemic infection model is higher than expected from in vitro results, and the in vitro activity is enhanced by addition of bovine serum. Here, we confirm that serum from various species, including humans, increases lysocin E antimicrobial activity, and identify apolipoprotein A-I (ApoA-I) as an enhancing factor. ApoA-I increases the antibacterial activity of lysocin E when added in vitro, and the antibiotic displays reduced activity in ApoA-I gene knockout mice. Binding of ApoA-I to lysocin E is enhanced by lipid II, a cell-wall synthesis precursor found in the bacterial membrane. Thus, the antimicrobial activity of lysocin E is potentiated through interactions with host serum proteins and microbial components.

Lysocin E is a lipopeptide with antibiotic activity against methicillin-resistant Staphylococcus aureus. Here, the authors show that the antimicrobial activity of lysocin E is potentiated through interactions with host serum proteins (such as apolipoprotein A-I) and bacterial membrane components.

Comparative analysis of COVID-19 case fatality rate between two waves in Nepal

The first COVID-19 case in Nepal was reported on January 23, 2020. Then infection, then, started to spread gradually, and October marked the most devastating increase in COVID-19 cases of the year 2020. Compared with the October 2020 peak in Nepal, the May 2021 peak of COVID-19 observed 2- and 10-fold rise in new cases and deaths per day, respectively. Given that this surprising increase in the death rate was not observed in other countries, this study analyzed the COVID-19 case fatality rates between the two peaks in Nepal. We found an increase in death rates among younger adults and people without comorbidities.

Large-Scale Screening and Identification of Novel Pathogenic Staphylococcus aureus Genes Using a Silkworm Infection Model

The regulatory network of virulence factors produced by the opportunistic pathogen Staphylococcus aureus is unclear and the functions of many uncharacterized genes in its genome remain to be elucidated. In this study, we screened 380 genes whose function was unassigned, utilizing gene-disrupted transposon mutants of the community-acquired methicillin-resistant S. aureus USA300 for pathogenicity in silkworms. We identified 10 strains with reduced silkworm killing ability. Among them, 8 displayed reduced virulence in a mouse model as evidenced by reduced colony-forming units in organs of infected mice. The role of each gene in pathogenicity was further confirmed by complementation and pathogenicity tests in silkworms, where we found that the phenotype was not restored in 1 strain. Additionally, some of the mutants displayed reduced hemolysis, proteolysis, pigment production, and survival in murine RAW 264.7 monocyte-macrophage cells. These newly identified genes involved in virulence will enhance our understanding of the pathogenicity of S. aureus.

Complete genome sequence and comparative genomic analysis of Enterococcus faecalis EF-2001, a probiotic bacterium

Enterococcus faecalis is a common human gut commensal bacterium. While some E. faecalis strains are probiotic, others are known to cause opportunistic infections, and clear distinction between these strains is difficult using traditional taxonomic approaches. In this study, we completed the genome sequencing of EF-2001, a probiotic strain, using our in-house hybrid assembly approach. Comparative analysis showed that EF-2001 was devoid of cytolysins, major factors associated with pathogenesis, and was phylogenetically distant from pathogenic E. faecalis V583. Genomic analysis of strains with a publicly available complete genome sequence predicted that drug-resistance genes- dfrE, efrA, efrB, emeA, and lsaA were present in all strains, and EF-2001 lacked additional drug-resistance genes. Core- and pan-genome analyses revealed a higher degree of genomic fluidity. We found 49 genes specific to EF-2001, further characterization of which may provide insights into its diverse biological activities. Our comparative genomic analysis approach could help predict the pathogenic or probiotic potential of E. faecalis leading to an early distinction based on genome sequences.

Clinical and epidemiological features of COVID-19 deaths in Nepal

Coronavirus disease 2019 (COVID-19), caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), has taken more than 1 million lives globally. This study, based on the official media releases of the Government of Nepal, analyses the clinical and epidemiological features of the individuals who died as a result of COVID-19 in Nepal from 23 January to 10 August 2020. We found that nearly half of the deaths were among people less than 50 years of age and being female increased the risk of death. The majority of deaths were associated with co-morbidities, the most common being cardiovascular diseases and diabetes followed by respiratory diseases. With the approaching festive season and relaxed lockdown, both government and citizens need to be more cautious about the severity of COVID-19 and take appropriate action.

Discovery of gramicidin A analogues with altered activities by multidimensional screening of a one-bead-one-compound library

Gramicidin A (1) is a peptide antibiotic that disrupts the transmembrane ion concentration gradient by forming an ion channel in a lipid bilayer. Although long used clinically, it is limited to topical application because of its strong hemolytic activity and mammalian cytotoxicity, likely arising from the common ion transport mechanism. Here we report an integrated high-throughput strategy for discovering analogues of 1 with altered biological activity profiles. The 4096 analogue structures are designed to maintain the charge-neutral, hydrophobic, and channel forming properties of 1. Synthesis of the analogues, tandem mass spectrometry sequencing, and 3 microscale screenings enable us to identify 10 representative analogues. Re-synthesis and detailed functional evaluations find that all 10 analogues share a similar ion channel function, but have different cytotoxic, hemolytic, and antibacterial activities. Our large-scale structure-activity relationship studies reveal the feasibility of developing analogues of 1 that selectively induce toxicity toward target organisms.

The strong hemolytic activity and mammalian cytotoxicity of gramicidin A, a peptide antibiotic, has hindered its non-topical clinical application. Here, the authors report a high-throughput strategy for the discovery of gramicidin A analogues with altered biological activity profiles.

A simple artificial diet available for research of silkworm disease models

This study was performed with the aim of making a very simple recipe of silkworm diet for research purposes, especially screening of drug candidates. We prepared a diet containing mulberry leaves powder and soybean flour at different ratios, fed them to fifth instar silkworm larvae, and observed their growth. We selected the diet with 1:1 ratio of mulberry powder and soybean flour, named MS-11, and used for further experiments. MS-11 diet was available for oral administration of drugs in silkworm hyperglycemic model and infection model. The availability of a simple artificial diet for experiments that require feeding silkworms will enhance the use of silkworms for biological, biotechnological, and pharmacological researches.

The Role of Amino Acid Substitution in HepT Toward Menaquinone Isoprenoid Chain Length Definition and Lysocin E Sensitivity in Staphylococcus aureus

OBJECTIVES

Staphylococcus aureus Smith strain is a historical strain widely used for research purposes in animal infection models for testing the therapeutic activity of antimicrobial agents. We found that it displayed higher sensitivity toward lysocin E, a menaquinone (MK) targeting antibiotic, compared to other S. aureus strains. Therefore, we further explored the mechanism of this hypersensitivity.

METHODS

MK production was analyzed by high-performance liquid chromatography and mass spectrometric analysis. S. aureus Smith genome sequence was completed using a hybrid assembly approach, and the MK biosynthetic genes were compared with other S. aureus strains. The hepT gene was cloned and introduced into S. aureus RN4220 strain using phage mediated recombination, and lysocin E sensitivity was analyzed by the measurement of colony-forming units.

RESULTS

We found that Smith strain produced MKs with the length of the side chain ranging between 8 and 10, as opposed to other S. aureus strains that produce MKs 7-9. We revealed that Smith strain possessed the classical pathway for MK biosynthesis like the other S. aureus. HepT, a polyprenyl diphosphate synthase involved in chain elongation of isoprenoid, in Smith strain harbored a Q25P substitution. Introduction of hepT from Smith to RN4220 led to the production of MK-10 and an increased sensitivity toward lysocin E.

CONCLUSION

We found that HepT was responsible for the definition of isoprenoid chain length of MKs and antibiotic sensitivity.

COVID-19: the current situation in Nepal

The recent global pandemic of novel coronavirus disease 2019 (COVID-19) is increasingly alarming. As of 21 June 2020, there are more than 8.7 million cases worldwide, with 460 000 deaths. Nepal is not an exception to COVID-19 and is currently facing a challenge to prevent the spread of infection. The analysis of the detected cases, severity and outcomes of the cases within a country is important to have a clear picture of where the pandemic is heading and what measures should be taken to curb the infection before it becomes uncontrollable. We collected data regarding all the cases, recoveries and deaths attributed to COVID-19 in Nepal starting from the first case on 23 January to 21 June 2020. At present, COVID-19 has spread all over Nepal, with a rapid increase in the number of new cases and deaths, which is alarming in a low-income country with an inadequate healthcare system like Nepal. Although the government implemented early school closure and lockdown, the management to contain COVID-19 does not appear to be adequate. Understanding the current situation regarding COVID-19 in Nepal is important for providing a direction towards proper management of the disease.

β-carboline chemical signals induce reveromycin production through a LuxR family regulator in Streptomyces sp. SN-593

Actinomycetes bacteria produce diverse bioactive molecules that are useful as drug seeds. To improve their yield, researchers often optimize the fermentation medium. However, exactly how the extracellular chemicals present in the medium activate secondary metabolite gene clusters remains unresolved. BR-1, a β-carboline compound, was recently identified as a chemical signal that enhanced reveromycin A production in Streptomyces sp. SN-593. Here we show that BR-1 specifically bound to the transcriptional regulator protein RevU in the reveromycin A biosynthetic gene cluster, and enhanced RevU binding to its promoter. RevU belongs to the LuxR family regulator that is widely found in bacteria. Interestingly, BR-1 and its derivatives also enhanced the production of secondary metabolites in other Streptomyces species. Although LuxR-N-acyl homoserine lactone systems have been characterized in Gram-negative bacteria, we revealed LuxR-β-carboline system in Streptomyces sp. SN-593 for the production of secondary metabolites. This study might aid in understanding hidden chemical communication by β-carbolines.

Validation of the Nepalese version of Recovery Experience Questionnaire

People with stressful situations tend to experience lower psychological well-being highlighting the importance of involvement in activities or strategies that have the potential to promote recovery after stressful work situations. This study aimed to validate the Nepalese version of the Recovery Experience Questionnaire (REQ-N), which evaluates how individuals unwind and recuperate from work in their leisure time. Registered nurses of three university hospitals (N = 438) in Nepal were asked to complete the REQ-N voluntarily and the data was analyzed using SPSS-20 and AMOS. Reliability was examined by using the Cronbach alpha coefficient. Factorial validity was examined by using exploratory and confirmatory factor analysis. Convergent validity was examined by examining the relationships with psychological distress, overall health, happiness, job performance and job satisfaction. Cronbach's alpha coefficients for four subscales ranged from 0.67 to 0.70. A hypothesized four-factor model fitted better to the data. As expected, mastery and control subscales correlated with psychological distress, overall health, happiness, job performance, and job satisfaction. However, psychological detachment subscale correlated with poor health and relaxation subscale correlated with low job satisfaction. The REQ-N displayed an acceptable level of internal-consistency reliability. The theory-based four-factor structure and the association with psychological distress, overall health, happiness, job performance and job satisfaction for mastery and control experience subscales supported the construct validity (including factor-based validity). However, some of the model fit statistics could not meet the minimum recommendations suggesting a need of a large study involving a heterogeneous population. Also, unexpected findings for psychological detachment and relaxation may reflect the culture and values of Nepalese people and need further research.

Complete Genome Sequence of Weissella hellenica 0916-4-2 and Its Comparative Genomic Analysis

Weissella genus from Leuconostocaceae family forms a group of Gram-positive lactic acid bacteria (LAB) that mostly reside in fermented foods and some have been isolated from the environment and vertebrates including humans. Currently there are 23 recognized species, 16 complete and 37 draft genome assemblies for this genus. Weissella hellenica has been found in various sources and is characterized by their probiotic and bacteriocinogenic properties. Despite its widespread importance, little attention has been paid to genomic characterization of this species with the availability of draft assembly of two species in the public database so far. In this manuscript, we identified W. hellenica 0916-4-2 from fermented kimchi and completed its genome sequence. Comparative genomic analysis identified 88 core genes that had interspecies mean amino acid identity of more than 65%. Whole genome phylogenetic analysis showed that three W. hellenica strains clustered together and the strain 0916-4-2 was close to strain WiKim14. In silico analysis for the secondary metabolites biosynthetic gene cluster showed that Weissella are far less producers of secondary metabolites compared to other members of Leuconostocaceae. The availability of the complete genome of W. hellenica 0916-4-2 will facilitate further comparative genomic analysis of Weissella species, including studies of its biotechnological potential and improving the nutritional value of various food products.

Molecular characterization of multi-drug resistant coagulase negative cocci in non-hospital environment

Antibiotic resistance crisis occasioned by sporadic appearance of multi-drug resistance (MDR) in human pathogens to clinically applied antimicrobials is a serious threat to global health. In this study, we investigated the drug resistant phenotype of Gram-positive cocci isolates from environment. Staphylococcus capitis and Staphylococcus haemolyticus colonies were isolated on mannitol-salt agar plates supplemented with tetracycline. Antibiotic susceptibility profile of the isolates via minimum inhibitory concentration (MIC) determination was examined. Isolates showed decreased sensitivity to clinically applied antimicrobial agents: tetracycline, kanamycin, erythromycin, norfloxacin, teicoplanin, and ampicillin. Genomic analysis demonstrated the presence of multiple antibiotic resistant genes in these bacteria, suggesting the origin of the multiple antimicrobials resistant phenotype. Tetracycline resistance of these isolates was transduced to Staphylococcus aureus-RN4220 strain. These findings indicate the presence of multiple antimicrobials resistant S. capitis and S. haemolyticus strain in a non-hospital setting. Moreover, the presence of plethora of genes responsible for MDR suggest that these strains could present potential threat to human health by serving as reservoir for lateral transference of antimicrobial resistance conferring foreign genetic elements to other clinically relevant pathogens.

GPI0363 inhibits the interaction of RNA polymerase with DNA inStaphylococcus aureus

We previously reported a therapeutically effective spiro-heterocyclic compound, GPI0363, that inhibits the transcription of Staphylococcus aureus via the primary sigma factor of RNA polymerase, SigA. Here, we demonstrated that GPI0363 shares no cross-resistance with the clinically used RNA polymerase inhibitors rifampicin and fidaxomicin. Furthermore, we found that GPI0363 bound to SigA of both GPI0363-susceptible and resistant strains, and inhibited the interaction of the RNA polymerase holoenzyme with DNA. In addition, the gene expression patterns following GPI0363 treatment were different from those following rifampicin treatment. These findings suggest that GPI0363 has a unique mechanism of action and can serve as a promising lead molecule to develop staphylococcal RNA polymerase inhibitors.

GPI0363 has a distinct mode of action via SigA and is active against bacteria resistant to clinically used RNAP inhibitors.

Utilization of Hybrid Assembly Approach to Determine the Genome of an Opportunistic Pathogenic Fungus, Candida albicans TIMM 1768

Candida albicans TIMM1768 is a highly virulent strain utilized as a model organism for the study of gastrointestinal and oral candidiasis. Despite being a model strain, identification of its genetic determinants of pathogenesis is hindered by the unavailability of its genome sequence. In this study, we determined the genome sequence of C. albicans TIMM1768 using reads obtained from portable MinION and benchtop Ion PGM sequencers. Genome annotation and a comparative analysis with published genomes revealed that the TIMM1768 strain was close to Candida albicans CHN1, and we identified a significant number of genes encoding for pathogenesis. The availability of the C. albicans TIMM1768 genome will facilitate comparative genomic analysis of Candida species, including studies of its virulence mechanisms and the development of treatment strategies for severe candidiasis.

Development of a Terpenoid-Production Platform in Streptomyces reveromyceticus SN-593

Terpenoids represent the largest class of natural products, some of which are resources for pharmaceuticals, fragrances, and fuels. Generally, mass production of valuable terpenoid compounds is hampered by their low production levels in organisms and difficulty of chemical synthesis. Therefore, the development of microbial biosynthetic platforms represents an alternative approach. Although microbial terpenoid-production platforms have been established in Escherichia coli and yeast, an optimal platform has not been developed for Streptomyces species, despite the large capacity to produce secondary metabolites, such as polyketide compounds. To explore this potential, we constructed a terpenoid-biosynthetic platform in Streptomyces reveromyceticus SN-593. This strain is unique in that it harbors the mevalonate gene cluster enabling the production of furaquinocin, which can be controlled by the pathway specific regulator Fur22. We simultaneously expressed the mevalonate gene cluster and subsequent terpenoid-biosynthetic genes under the control of Fur22. To achieve improved fur22 gene expression, we screened promoters from S. reveromyceticus SN-593. Our results showed that the promoter associated with rvr2030 gene enabled production of 212 ± 20 mg/L botryococcene to levels comparable to those previously reported for other microbial hosts. Given that the rvr2030 gene encodes for an enzyme involved in the primary metabolism, these results suggest that optimized expression of terpenoid-biosynthetic genes with primary and secondary metabolism might be as important for high yields of terpenoid compounds as is the absolute expression level of a target gene(s).

Prevalence and correlates of substance use among health care students in Nepal: a cross sectional study

Background

Substance use among health care students threatens professional standards and the delivery of quality services, potentially placing the public at risk. Therefore, our study aims to determine the prevalence and correlates associated with substance use among Nepalese health care students.

Method

A cross-sectional survey using a self-administered health professional questionnaire was conducted among pharmacy, nursing, and public health students at three universities in Nepal in 2010.

Results

We analyzed data from 407 respondents (response rate, 82%) with a mean age of 22 years (standard deviation = 3.71). The overall lifetime prevalence of substance use (i. e., illegal use of prescription drugs and illegal drug use) was 42.8%. Marijuana was the most commonly used illegal drug (8.8%) and minor opiates (e.g., codeine cough syrups) were the most widely used illegal prescription drugs (32.4%). Substance use was directly associated with cigarette smoking, peer influence, and heavy drinking. In addition, respondents reported some major and minor dysfunctions because of their substance use.

Conclusion

The prevalence of substance use among health care students at the three universities in Nepal was high. Peer influence, cigarette smoking, and heavy drinking were significant predictors of substance use.

Electronic supplementary material

The online version of this article (10.1186/s12889-017-4980-6) contains supplementary material, which is available to authorized users.

Total Synthesis and Biological Mode of Action of WAP-8294A2: A Menaquinone-Targeting Antibiotic

WAP-8294A2 (lotilibcin, 1) is a potent antibiotic with superior in vivo efficacy to vancomycin against methicillin-resistant Staphylococcus aureus (MRSA). Despite the great medical importance, its molecular mode of action remains unknown. Here we report the total synthesis of complex macrocyclic peptide 1 comprised of 12 amino acids with a β-hydroxy fatty-acid chain, and its deoxy analogue 2. A full solid-phase synthesis of 1 and 2 enabled their rapid assembly and the first detailed investigation of their functions. Compounds 1 and 2 were equipotent against various strains of Gram-positive bacteria including MRSA. We present evidence that the antimicrobial activities of 1 and 2 are due to lysis of the bacterial membrane, and their membrane-disrupting effects depend on the presence of menaquinone, an essential factor for the bacterial respiratory chain. The established synthetic routes and the menaquinone-targeting mechanisms provide valuable information for designing and developing new antibiotics based on their structures.

Unified Total Synthesis of Polyoxins J, L, and Fluorinated Analogues on the Basis of Decarbonylative Radical Coupling Reactions

Polyoxins J (1 a) and L (1 b) are important nucleoside antibiotics. The complex and densely functionalized dipeptide structures of 1 a and 1 b contain thymine and uracil nucleobases, respectively. Herein we report the unified total synthesis of 1 a, 1 b, and their artificial analogues 1 c and 1 d with trifluorothymine and fluorouracil structures. Decarbonylative radical coupling between α-alkoxyacyl tellurides and a chiral glyoxylic oxime ether led to chemo- and stereoselective construction of the ribonucleoside α-amino acid structures of 1 a-d without damaging the preinstalled nucleobases. The high applicability of the radical-based methodology was further demonstrated by preparation of the trihydroxynorvaline moiety of 1 a-d. The two amino acid fragments were connected and elaborated into 1 a-d (longest linear sequence: 11 steps). Compounds 1 a and 1 b assembled in this way exhibited potent activity against true fungi, while only 1 d was active against Gram-positive bacteria.

Genomic analysis of vancomycin-resistant Staphylococcus aureus VRS3b and its comparison with other VRSA isolates

High-level vancomycin resistance among Staphylococcus aureus poses a grave threat to global health as the treatment options for this pathogen are very limited. A detailed evaluation of the genetic background of vancomycin-resistant S. aureus (VRSA) is expected to facilitate the understanding of its origin and pathogenicity. In this study, we performed the genetic analysis of the clinical VRSA isolates and identified the genetic basis of resistance to multiple antibiotics among these strains, based on the available draft genome sequences. In addition, we generated the draft genome of the strain VRS3b, which was considered to be same as VRS3a based on its isolation from the same patient. We found that strain VRS3b did not harbor the genes responsible for tetracycline and gentamicin, which was further confirmed by the sensitivity towards these antibiotics. Our results suggest that the strains VRS3a and VRS3b are different from the view of antibiotic resistance and highlight the possibility of generation of two distinct VRSA strains from the same patient.

A Novel Spiro-Heterocyclic Compound Identified by the Silkworm Infection Model Inhibits Transcription in Staphylococcus aureus

Synthetic compounds are a vital source of antimicrobial agents. To uncover therapeutically effective antimicrobial agents from a chemical library, we screened over 100,000 synthetic compounds for in vitro antimicrobial activity against methicillin-resistant Staphylococcus aureus and evaluated the in vivo therapeutic effectiveness of the hits in S. aureus-infected silkworms. Three antimicrobial agents exhibited therapeutic effects in the silkworm infection model. One of these, GPI0363, a novel spiro-heterocyclic compound, was bacteriostatic and inhibited RNA synthesis in S. aureus cells. GPI0363-resistant S. aureus strains harbored a point mutation in the gene encoding the primary sigma factor, SigA, of RNA polymerase, and this mutation was responsible for the resistance to GPI0363. We further revealed that GPI0363 could bind to SigA, inhibit promoter-specific transcription in vitro, and prolong the survival of mice infected with methicillin-resistant S. aureus. Thus, GPI0363 is an attractive candidate therapeutic agent against drug-resistant S. aureus infections.

Advantages of the Silkworm As an Animal Model for Developing Novel Antimicrobial Agents

The demand for novel antibiotics to combat the global spread of multi drug-resistant pathogens continues to grow. Pathogenic bacteria and fungi that cause fatal human infections can also kill silkworms and the infected silkworms can be cured by the same antibiotics used to treat infections in the clinic. As an invertebrate model, silkworm model is characterized by its convenience, low cost, no ethical issues. The presence of conserved immune response and similar pharmacokinetics compared to mammals make silkworm infection model suitable to examine the therapeutic effectiveness of antimicrobial agents. Based on this, we utilized silkworm bacterial infection model to screen the therapeutic effectiveness of various microbial culture broths and successfully identified a therapeutically effective novel antibiotic, lysocin E, which has a novel mode of action of binding to menaquinone, thus leading to membrane damage and bactericidal activity. The similar approach to screen potential antibiotics resulted in the identification of other therapeutically effective novel antibiotics, such as nosokomycin and ASP2397 (VL-2397). In this regard, we propose that the silkworm antibiotic screening model is very effective for identifying novel antibiotics. In this review, we summarize the advantages of the silkworm model and propose that the utilization of silkworm infection model will facilitate the discovery of novel therapeutically effective antimicrobial agents.

Lysobacter species: a potential source of novel antibiotics

Infectious diseases threaten global health due to the ability of microbes to acquire resistance against clinically used antibiotics. Continuous discovery of antibiotics with a novel mode of action is thus required. Actinomycetes and fungi are currently the major sources of antibiotics, but the decreasing rate of discovery of novel antibiotics suggests that the focus should be changed to previously untapped groups of microbes. Lysobacter species have a genome size of ~6 Mb with a relatively high G + C content of 61-70 % and are characterized by their ability to produce peptides that damage the cell walls or membranes of other microbes. Genome sequence analysis revealed that each Lysobacter species has gene clusters for the production of 12-16 secondary metabolites, most of which are peptides, thus making them 'peptide production specialists'. Given that the number of antibiotics isolated is much lower than the number of gene clusters harbored, further intensive studies of Lysobacter are likely to unearth novel antibiotics with profound biomedical applications. In this review, we summarize the structural diversity, activity and biosynthesis of lysobacterial antibiotics and highlight the importance of Lysobacter species for antibiotic production.

Lysobacter species: a potential source of novel antibiotics

Infectious diseases threaten global health due to the ability of microbes to acquire resistance against clinically used antibiotics. Continuous discovery of antibiotics with a novel mode of action is thus required. Actinomycetes and fungi are currently the major sources of antibiotics, but the decreasing rate of discovery of novel antibiotics suggests that the focus should be changed to previously untapped groups of microbes. Lysobacter species have a genome size of ~6 Mb with a relatively high G + C content of 61-70 % and are characterized by their ability to produce peptides that damage the cell walls or membranes of other microbes. Genome sequence analysis revealed that each Lysobacter species has gene clusters for the production of 12-16 secondary metabolites, most of which are peptides, thus making them 'peptide production specialists'. Given that the number of antibiotics isolated is much lower than the number of gene clusters harbored, further intensive studies of Lysobacter are likely to unearth novel antibiotics with profound biomedical applications. In this review, we summarize the structural diversity, activity and biosynthesis of lysobacterial antibiotics and highlight the importance of Lysobacter species for antibiotic production.

Identification of Middle Chain Fatty Acyl-CoA Ligase Responsible for the Biosynthesis of 2-Alkylmalonyl-CoAs for Polyketide Extender Unit

Understanding the biosynthetic mechanism of the atypical polyketide extender unit is important for the development of bioactive natural products. Reveromycin (RM) derivatives produced by Streptomyces sp. SN-593 possess several aliphatic extender units. Here, we studied the molecular basis of 2-alkylmalonyl-CoA formation by analyzing the revR and revS genes, which form a transcriptional unit with the revT gene, a crotonyl-CoA carboxylase/reductase homolog. We mainly focused on the uncharacterized adenylate-forming enzyme (RevS). revS gene disruption resulted in the reduction of all RM derivatives, whereas reintroduction of the gene restored the yield of RMs. Although RevS was classified in the fatty acyl-AMP ligase clade based on phylogenetic analysis, biochemical characterization revealed that the enzyme catalyzed the middle chain fatty acyl-CoA ligase (FACL) but not the fatty acyl-AMP ligase activity, suggesting the molecular evolution for acyl-CoA biosynthesis. Moreover, we examined the in vitro conversion of fatty acid into 2-alkylmalonyl-CoA using purified RevS and RevT. The coupling reaction showed efficient conversion of hexenoic acid into butylmalonyl-CoA. RevS efficiently catalyzed C8-C10 middle chain FACL activity; therefore, we speculated that the acyl-CoA precursor was truncated via β-oxidation and converted into (E)-2-enoyl-CoA, a RevT substrate. To determine whether the β-oxidation process is involved between the RevS and RevT reaction, we performed the feeding experiment using [1,2,3,4-(13)C]octanoic acid. (13)C NMR analysis clearly demonstrated incorporation of the [3,4-(13)C]octanoic acid moiety into the structure of RM-A. Our results provide insight into the role of uncharacterized RevS homologs that may catalyze middle chain FACL to produce a unique polyketide extender unit.

Nepalese pharmacy students' perceptions regarding mental disorders and pharmacy education

OBJECTIVE

To determine Nepalese pharmacy students' perceptions of whether mental disorders impact performance in pharmacy school.

METHOD

All first- and third-year undergraduate pharmacy students (n=226) in Nepal were invited to complete a modified version of the Mental Illness Performance Scale.

RESULTS

Among the 200 respondents (response rate 88.5%), 14% reported that they had a mental disorder. The majority (92%) of third-year students agreed or strongly agreed that depression would interfere with a student's academic performance. Almost half of first-year students agreed or strongly agreed that alcohol or drug abuse would be grounds for both rejecting an applicant from pharmacy school (49%) and dismissal of a student from pharmacy school (46%).

CONCLUSIONS

Students perceived a high level of academic impairment associated with mental disorders, but the majority did not perceive that mental disorders were grounds for dismissal from or rejection of entry to pharmacy school. Students' attitudes may discourage them from seeking help or providing mental health support to others.