New approaches in the treatment of bacterial infections

Streptomyces iakyrus TA 36 as First-Reported Source of Quinone Antibiotic γ-Rubromycin

A wide range of bioactive compounds with potential medical applications are produced by members of the genus Streptomyces. A new actinomycete producer of the antibiotic γ-rubromycin, designated TA 36, was isolated from an alpine soil sample collected in Peru (Machu Picchu). Morphological, physiological and biochemical characteristics of the strain, together with data obtained via phylogenetic analysis and MALDI-TOF MS, were used for the correct identification of the isolate. The isolate TA 36 showed morphological characteristics that were consistent with its classification within the genus Streptomyces. Phylogenetic analysis based on 16S rRNA gene sequences showed that the TA 36 strain was most similar to S. iakyrus and S. violaceochromogenes with 99% similarity. Phylogenetic analysis together with the profile of whole cell proteins indicated that the strain tested could be identified as S. iakyrus TA 36. The crude extract Ext.5333.TA 36 showed various effects against the tested organisms with strong antimicrobial activity in the growth of Staphylococcus aureus (Newman) (MIC value of 0.00195 µg/µL). HPLC fractionation and LC/MS analysis of the crude extract led to the identification of the quinone antibiotic γ-rubromycin, a promising antitumour and antibacterial antibiotic. To the best of our knowledge, there is currently no report on the production of γ-rubromycin by S. iakyrus. Therefore, this study suggests S. iakyrus TA 36 as the first-reported source of this unique bioactive secondary metabolite.

Effects of sulfated β-glucan from Saccharomyces cerevisiae on growth performance, antioxidant ability, nonspecific immunity, and intestinal flora of the red swamp crayfish (Procambarus clarkii)

The aim of this study was to examine the combined effects of sulfated β-Glucan from Saccharomyces cerevisiae (sGSC) on growth performance, antioxidant ability, nonspecific immunity, and intestinal flora of the red swamp crayfish (Procambarus clarkii). Four experimental diets (sGSC25, sGSC50, sGSC100 and sGSC200) with different levels of sGSC (0.025%, 0.05%, 0.1% and 0.2% in diet, respectively) were fed to juvenile crayfish (average weight: 2.5 ± 0.5 g) for 8 weeks. The control diet was given with 2000 mg/kg GSC (GSC200 group). The based control diet was given without sGSC or GSC (blank group). Each group had 3 parallel test pools, 20 crayfish were reared in each pool. At the end of the growth trial, adding dietary 0.025%-0.1% sGSC could significantly improve the growth performance, antioxidant capacity and immunity of crayfish. Compared with GSC, sGSC had a better effect at lower concentration. Higher concentration of sGSC (>0.1%) would cause some side effects. sGSC also could improve the structure of the intestinal flora and optimize the function of the flora. sGSC would increase the abundances of probiotics such as Hafnia and Acinetobacter, and decreases the abundances of maleficent bacteria such as Enterobacteriaceae. Higher concentration of sGSC (>0.1%) would increase the abundance of Aeromonas. To conclude, 0.025%-0.1% sGSC can be used as a supplement in crayfish feed to increase growth, immunity, and antioxidant capacity and improve the structure of intestinal flora. These results provided a theoretical basis for the application of sGSC instead of GSC in crayfish breeding. It will be necessary to further study the optimal concentration of sGSC in feed additives in different growth stages of crayfish in the future.

The role of soils in provision of genetic, medicinal and biochemical resources

Intact, 'healthy' soils provide indispensable ecosystem services that largely depend on the biotic activity. Soil health is connected with human health, yet, knowledge of the underlying soil functioning remains incomplete. This review highlights selected services, i.e. (i) soil as a genetic resource and hotspot of biodiversity, forming the basis for providing (ii) biochemical resources and (iii) medicinal services and goods. Soils harbour an unrivalled biodiversity of organisms, especially microorganisms. Some of the abilities of autochthonous microorganisms and their relevant enzymes serve (i) to improve natural soil functions and in particular plant growth, e.g. through beneficial plant growth-promoting, symbiotic and mycorrhizal microorganisms, (ii) to act as biopesticides, (iii) to facilitate biodegradation of pollutants for soil bioremediation and (iv) to yield enzymes or chemicals for industrial use. Soils also exert direct effects on human health. Contact with soil enriches the human microbiome, affords protection against allergies and promotes emotional well-being. Medicinally relevant are soil substrates such as loams, clays and various minerals with curative effects as well as pharmaceutically active organic chemicals like antibiotics that are formed by soil microorganisms. By contrast, irritating minerals, soil dust inhalation and misguided soil ingestion may adversely affect humans. This article is part of the theme issue 'The role of soils in delivering Nature's Contributions to People.

Periodontal pathogens promote cancer aggressivity via TLR/MyD88 triggered activation of Integrin/FAK signaling that is therapeutically reversible by a probiotic bacteriocin

Epidemiological studies reveal significant associations between periodontitis and oral cancer. However, knowledge about the contribution of periodontal pathogens to oral cancer and potential regulatory mechanisms involved is limited. Previously, we showed that nisin, a bacteriocin and commonly used food preservative, reduced oral cancer tumorigenesis and extended the life expectancy in tumor-bearing mice. In addition, nisin has antimicrobial effects on key periodontal pathogens. Thus, the purpose of this study was to test the hypothesis that key periodontal pathogens (Porphyromonas gingivalis, Treponema denticola, and Fusobacterium nucleatum) promote oral cancer via specific host-bacterial interactions, and that bacteriocin/nisin therapy may modulate these responses. All three periodontal pathogens enhanced oral squamous cell carcinoma (OSCC) cell migration, invasion, tumorsphere formation, and tumorigenesis in vivo, without significantly affecting cell proliferation or apoptosis. In contrast, oral commensal bacteria did not affect OSCC cell migration. Pathogen-enhanced OSCC cell migration was mediated via integrin alpha V and FAK activation, since stably blocking alpha V or FAK expression abrogated these effects. Nisin inhibited these pathogen-mediated processes. Further, Treponema denticola induced TLR2 and 4 and MyD88 expression. Stable suppression of MyD88 significantly inhibited Treponema denticola-induced FAK activation and abrogated pathogen-induced migration. Together, these data demonstrate that periodontal pathogens contribute to a highly aggressive cancer phenotype via crosstalk between TLR/MyD88 and integrin/FAK signaling. Nisin can modulate these pathogen-mediated effects, and thus has therapeutic potential as an antimicrobial and anti-tumorigenic agent.

Marine actinomycetes Nocardiopsis alba MCCB 110 has immunomodulatory property in the tiger shrimp Penaeus monodon

Shrimp farming constitutes an important source of revenue and employment in many developing countries. However, the shrimp industry has always been plagued with infectious diseases having varied aetiologies. Dominated by non - specific immune mechanism, preventive health care strategy is the most appropriate approach to protect the crop. The present study evaluated the efficacy of an actinomycete, Nocardiopsis alba MCCB 110 in eliciting non - specific immune mechanism in Penaeus monodon having Vibrio harveyi as the challenge organism. Haemocyte count, total protein, phenoloxidase, reactive oxygen intermediates, acid and alkaline phosphatase as well as the gene expression of proPO, peroxinectin, transglutaminase, alpha 2-macroglobulin, astakine, crustin, and penaeidin-3 were evaluated. The results demonstrated that the phenoloxidase, respiratory burst, total protein, acid and alkaline phosphatases were higher in the haemolymph of shrimps fed with Nocardiopsis alba MCCB 110 incorporated feed before and after challenge with Vibrio harveyi, compared to those of placebo fed animals. Up-regulation of six immune genes (alpha 2 macroglobulin, penaeidin -3, transglutaminase, proPO, crustin and peroxinectin) during the post-challenge were recorded. Survival of shrimp among the Nocardiopsis alba administered ones was 83% while it was 50% in placebo fed group. The elevated levels of nonspecific immune gene transcripts and concurrent increase in non specific immunity besides the higher survival rate in the Nocardiopsis alba administered group demonstrated the immunomodulatory property of the marine actinomycete Nocardiopsis alba MCCB 110 in the tiger shrimp Penaeus monodon, and on administering it through diet shrimp could be protected from vibriosis especially of V. harveyi.

Isolation and characterization of bioactive compounds with antibacterial, antioxidant and enzyme inhibitory activities from marine-derived rare actinobacteria, Nocardiopsis sp. SCA21

A rare actinobacteria strain designated SCA21, producing bioactive metabolites was isolated from marine sediment of Havelock Island, Andaman and Nicobar Islands, India. Analysis of 16S rRNA sequences suggested that the strain SCA21 belonged to the genus Nocardiopsis. Chemical investigation of the fermentation broth led to the isolation of two pure bioactive compounds (1-2). Compound 1: 4-bromophenol, a bromophenol derivative; Compound 2: Bis (2-ethylhexyl) phthalate, a phthalate ester. The structure of compound 1 and 2 were elucidated by the detailed analysis of FT-IR, HR-ESI-MS, 1D and 2D NMR, along with literature data analysis. The isolated metabolites were evaluated for enzyme inhibition activity against α-glucosidase and α-amylase, free radical scavenging activity against DPPH and ABTS radicals, metal chelating and antibacterial activity against clinical pathogens. 1 and 2 exhibited remarkable enzyme inhibitory activities against α-glucosidase. However, Compound 2 was found less active against α-amylase. They showed significant free radical scavenging activity against DPPH and ABTS radicals. In addition, except the strain Salmonella typhi ATCC 25241 and Listeria cytogens ATCC 13932, 1 and 2 showed broad spectrum inhibitory activity against MRSA ATCC NR-46171, MRSA ATCC-46071, Klebsiella pneumonia ATCC 13883, Bacillus subtilis ATCC 6633, Staphylococcus aureus ATCC 12600. In conclusion, to best of our knowledge these findings are the first report of isolation of 4-bromophenol and Bis (2-ethylhexyl) phthalate from genus Nocardiopsis, thus suggesting that rare actinomycetes are promising source of therapeutically important bioactive metabolites.

Microdialysis combined with liquid chromatography-tandem mass spectrometry for the quantitation of gemifloxacin and its application to a muscle penetration study in healthy and MRSA-infected rats

Pharmacological efficacy is based on the drug concentration in target tissues, which usually cannot be represented by the plasma concentration. The purpose of this study was to compare the pharmacokinetic characteristics of gemifloxacin in plasma and skeletal muscle and evaluate its tissue penetration in both healthy and MRSA (methicillin-resistant Staphylococcus aureus)-infected rats. A microdialysis (MD) combined with liquid chromatography-tandem mass spectrometry (LC-MS/MS) method was developed and validated to determine free gemifloxacin concentrations in rat plasma and skeletal muscle simultaneously. The in vivo recoveries of MD were 23.21% ± 3.42% for skeletal muscle and 20.62% ± 3.19% for plasma, and were concentration independent. We provided evidence that the method developed here meets FDA requirements. Additionally, this method was successfully applied to the determination of free gemifloxacin in rats. Muscle and blood dialysates were collected after an 18 mg/kg intravenous bolus dose. The mean areas under the concentration-time curves (AUCs) from 0 to 9 h for skeletal muscle and plasma were 3641.50 ± 915.65 h*ng/mL and 7068.32 ± 1964.19 h*ng/mL in MRSA-infected rats and 3774.72 ± 700.36 h*ng/mL and 6927.49 ± 1714.86 h*ng/mL in healthy rats, respectively. There was no significant difference (P>0.05) in gemifloxacin exposure between healthy rats and MRSA-infected rats for plasma or muscle. The low ratio of AUC0-9 muscle to AUC0-9 plasma suggested lower drug exposure in skeletal muscle than in plasma for both healthy and MRSA-infected rats. Our study suggested that the administration of gemifloxacin according to drug levels in plasma to treat local infection is unreasonable and might result in an inadequate dose regimen.

Phenolic compounds as antioxidants and chemopreventive drugs from Streptomyces cellulosae strain TES17 isolated from rhizosphere of Camellia sinensis

BACKGROUND

Oxidative stress in an intracellular environment created by the accumulation of reactive oxygen species results in oxidative damage to biomolecules which ultimately become a hallmark for severe diseases like cancer, aging, diabetes, and cardiovascular and neurodegenerative diseases.

METHODS

Various in vitro assays were employed to assess the antioxidant potential of strain, DNA protective activity was demonstrated using DNA nicking assay and cytotoxicity of the extract was evaluated using MTT assay. Further identification of the compounds was done using UPLC analysis.

RESULTS

The extract of Streptomyces cellulosae strain TES17 demonstrated significant antioxidant activity with percentage inhibition of 78.47 ± 0.23, 91.08 ± 0.98 and 82.08 ± 0.93 for DPPH, ABTS and superoxide radical assays at 5 mg/mL, respectively. Total antioxidant and reducing power were found to be 76.93 ± 0.76 and 231.96 ± 0.51 mg AAE/100 mg of dry extract, respectively. Moreover, the extract was shown to inhibit lipid peroxidation upto 67.18 ± 1.9% at 5 mg/mL. TPC and TFC measured in the extract was 55 mg GAE/100 mg and 11.17 ± 4.05 mg rutin/100 mg, respectively. The protective nature of the TES17 extract to oxidative stress induced damaged DNA was shown by percentage of supercoiled DNA i.e. Form I was increased from 26.38 to 38.20% at concentrations ranging from 2 μg to 10 μg. TES17 extract also showed the cytotoxic activity against lung cancer cell line with 74.7 ± 1.33% inhibition whereas, limited toxicity was observed against normal cell line with percentage viability of 87.71 ± 6.66 at same concentration (30 μg/mL) tested. The antioxidant capacity of extract was well correlated with its TPC and TFC and this in turn was in keeping with the UPLC analysis which also revealed the presence of phenolic compounds that were responsible for the antioxidant and cytotoxic potential of S. cellulosae strain TES17.

CONCLUSIONS

The present study describes that S. cellulosae strain TES17 isolated from the rhizosphere of Camellia sinensis (tea) plant; produces potent compounds with antioxidant activity, further might be developed into therapeutic drugs to combat oxidative stress.

Antimicrobial nisin acts against saliva derived multi-species biofilms without cytotoxicity to human oral cells

Objectives: Nisin is a lantibiotic widely used for the preservation of food and beverages. Recently, investigators have reported that nisin may have clinical applications for treating bacterial infections. The aim of this study was to investigate the effects of ultra pure food grade Nisin ZP (>95% purity) on taxonomically diverse bacteria common to the human oral cavity and saliva derived multi-species oral biofilms, and to discern the toxicity of nisin against human cells relevant to the oral cavity.

Methods: The minimum inhibitory concentrations and minimum bactericidal concentrations of taxonomically distinct oral bacteria were determined using agar and broth dilution methods. To assess the effects of nisin on biofilms, two model systems were utilized: a static and a controlled flow microfluidic system. Biofilms were inoculated with pooled human saliva and fed filter-sterilized saliva for 20–22 h at 37°C. Nisin effects on cellular apoptosis and proliferation were evaluated using acridine orange/ethidium bromide fluorescent nuclear staining and lactate dehydrogenase activity assays.

Results: Nisin inhibited planktonic growth of oral bacteria at low concentrations (2.5–50 μg/ml). Nisin also retarded development of multi-species biofilms at concentrations ≥1 μg/ml. Specifically, under biofilm model conditions, nisin interfered with biofilm development and reduced biofilm biomass and thickness in a dose-dependent manner. The treatment of pre-formed biofilms with nisin resulted in dose- and time-dependent disruption of the biofilm architecture along with decreased bacterial viability. Human cells relevant to the oral cavity were unaffected by the treatment of nisin at anti-biofilm concentrations and showed no signs of apoptotic changes unless treated with much higher concentrations (>200 μg/ml).

Conclusion: This work highlights the potential therapeutic value of high purity food grade nisin to inhibit the growth of oral bacteria and the development of biofilms relevant to oral diseases.

In vitro antimicrobial, antioxidant and cytotoxic properties of Streptomyces lavendulae strain SCA5

BACKGROUND

Actinomycetes are Gram-positive, often filamentous, bacteria known for their unsurpassed capacity for the production of secondary metabolites with diverse biological activities. The aim of the present study was to evaluate the antimicrobial, cytotoxic and antioxidant properties of Streptomyces lavendulae strain SCA5.

RESULTS

The ethyl acetate extract of SCA5 broth (EA-SCA5) showed antimicrobial activity with MIC value of 31.25 μg/ml. EA-SCA5 showed good antioxidant potential by scavenging 2, 2-diphenyl-picrylhydrazyl (DPPH) (IC50 507.61 ± 0.66 μg/ml), hydroxyl radical (IC50 617.84 ± 0.57 μg/ml), nitric oxide (IC50 730.92 ± 0.81 μg/ml) and superoxide anion radical (IC50 864.71 ± 1.15 μg/ml). The EA-SCA5 also showed strong suppressive effect on rat liver lipid peroxidation (IC50 838.83 ± 1.18 μg/ml). The total phenolic content of SCA5 was 577.12 mg of GAE equivalents/gram extract. EA-SCA5 exhibited cytotoxic activity on A549 adenocarcinoma lung cancer cell line. It showed 84.9% activity at 500 μg/ml with IC50 value of 200 μg/ml. The gas chromatography mass spectrometry (GC-MS) analysis revealed the presence of one major bioactive compound actinomycin C2.

CONCLUSIONS

The results of this study indicate that the EA-SCA5 could be probed further for isolating some medically useful compounds.

Cytotoxicity and antioxidant activity of 5-(2,4-dimethylbenzyl)pyrrolidin-2-one extracted from marine Streptomyces VITSVK5 spp

The aim of the present study was to evaluate the cytotoxicity and antioxidant activity of 5-(2,4-dimethylbenzyl)pyrrolidin-2-one (DMBPO) extracted from marine Streptomyces VITSVK5 spp. The strain was isolated from sediment samples collected at the Marakkanam coast of Bay of Bengal, India. Systematic screening of isolates for anti-Aspergillus activity resulted in the identification of Streptomyces species designated as Streptomyces VITSVK5 spp. Bioactivity guided extraction and purification yielded a compound 5-(2,4-dimethylbenzyl)pyrrolidin-2-one (DMBPO) and was tested for cytotoxicity and antioxidant activity. The structure of the extracted compound was established by spectroscopic studies and identified as 5-(2,4-dimethylbenzyl)pyrrolidin-2-one (DMBPO). DMBPO exhibited cytotoxic activity on HEP 2 and Hep G2 cell lines with the IC50 value of 2.8 μg/ml and 8.3 μg/ml, respectively, as compared to Vero cell line (22.6). DMBPO showed the hemolytic EC50 value of 288 μg/ml on human erythrocytes. DMBPO treatment showed fewer (31.7%) aberrations, gaps and chromatid breaks as compared to untreated controls (27.8%) of human chromosomes. DMBPO also exhibited significant (44.13% at 5 μg/ml DMBPO) DPPH radical scavenging activity and total antioxidant activity (50.10% at 5 μg/ml DMBPO). The results of this study showed that DMBPO is cytotoxic to cancer cells and possesses antioxidant property.

In vitro activity of 5-(2,4-dimethylbenzyl) pyrrolidin-2-one extracted from marine Streptomyces VITSVK5 spp. against fungal and bacterial human pathogens

BACKGROUND

Pharmacological screening and usage of natural products for the treatment of human diseases has had a long history from traditional medicine to modern drugs. The majority of modern drugs are reported to be mostly from natural products.

OBJECTIVE

The aim of the present study was to evaluate the inhibitory activity of 5-(2,4-dimethylbenzyl) pyrrolidin-2-one (DMBPO) extracted from marine Streptomyces VITSVK5 spp. isolated from sediment samples collected at Marakkanam coast of Bay of Bengal, India.

METHODS

The lead compound was isolated by bioactive guided extraction and purified by silica gel column chromatography. Structural elucidation of the lead compound was carried out by using UV, FT-IR, (1)H NMR, (13)C NMR, DEPT and HR-MS spectral data.

RESULTS

Systematic screening of isolates for antimicrobial activity lead to identification of a potential strain, Streptomyces VITSVK5 spp. (GQ848482). Bioactivity guided extraction yielded a compound DMBPO and its inhibitory activity was tested against selected bacterial and fungal strains. DMBPO showed maximal activity against Escherichia coli with a MIC value of 187 μg/ml, followed by Klebsiella pneumoniae (MIC of 220 μg/ml and 10.3mm zone of inhibition), Staphylococcus aureus (MIC of >1000 μg/ml and 4.4mm zone of inhibition) and Bacillus subtilis (MIC of 850 μg/ml and 2.6mm zone of inhibition). Furthermore, DMBPO was found to be a potent inhibitor of opportunistic fungal pathogens too. It showed a maximum activity against Aspergillus niger with a MIC value of 1 μg/ml and 28 mm zone of inhibition.

CONCLUSION

The result of this study indicates that DMBPO possess antibiotic activity to selected bacterial and fungal pathogens and exhibited better activity against fungi than bacteria.

Mupirocin: biosynthesis, special features and applications of an antibiotic from a gram-negative bacterium

Mupirocin is a polyketide antibiotic produced by Pseudomonas fluorescens. The biosynthetic cluster encodes 6 type I polyketide synthase multifunctional proteins and 29 single function proteins. The biosynthetic pathway belongs to the trans-AT group in which acyltransferase activity is provided by a separate polypeptide rather than in-cis as found in the original type I polyketide synthases. Special features of this group are in-cis methyltransferase domains and a trans-acting HMG-CoA synthase-cassette which insert α- and β- methyl groups respectively while enoyl reductase domains are absent from the condensing modules. In addition, for the mupirocin system, there is no obvious loading mechanism for initiation of the polyketide chain and many aspects of the pathway remain to be elucidated. Mupirocin inhibits isoleucyl-tRNA synthetase and has been used since 1985 to help prevent infection by methicillin-resistant Staphylococcus aureus, particularly within hospitals. Resistance to mupirocin was first detected in 1987 and high-level resistance in S. aureus is due to a plasmid-encoded second isoleucyl-tRNA synthetase, a more eukaryotic-like enzyme. Recent analysis of the biosynthetic pathway for thiomarinols from marine bacteria opens up possibilities to modify mupirocin so as to overcome this resistance.

Discovery of novel inhibitors of Streptococcus pneumoniae based on the virtual screening with the homology-modeled structure of histidine kinase (VicK)

Background

Due to the widespread abusage of antibiotics, antibiotic-resistance in Streptococcus pneumoniae (S. pneumoniae) has been increasing quickly in recent years, and it is obviously urgent to develop new types of antibiotics. Two-component systems (TCSs) are the major signal transduction pathways in bacteria and have emerged as potential targets for antibacterial drugs. Among the 13 pairs of TCSs proteins presenting in S. pneumoniae, VicR/K is the unique one essential for bacterium growth, and block agents to which, if can be found, may be developed as effective antibiotics against S. pneumoniae infection.

Results

Using a structure-based virtual screening (SBVS) method, 105 compounds were computationally identified as potential inhibitors of the histidine kinase (HK) VicK protein from the compound library SPECS. Six of them were then validated in vitro to be active in inhibiting the growth of S. pneumoniae without obvious cytotoxicity to Vero cell. In mouse sepsis models, these compounds are still able to decrease the mortality of the mice infected by S. pneumoniae and one compound even has significant therapeutic effect.

Conclusion

To our knowledge, these compounds are the first reported inhibitors of HK with antibacterial activity in vitro and in vivo, and are novel lead structures for developing new drugs to combat pneumococcal infection.

The empiric treatment of nosocomial intra-abdominal infections

The treatment of complicated intra-abdominal infections continues to challenge physicians, primarily because of the polymicrobial nature of these infections coupled with the high risk of complications and even death among the more severe patients. The initial selection of antimicrobial therapy for treatment of nosocomial intraabdominal infections is extremely important because an association has been shown between inappropriate empiric antimicrobial therapy and delayed clinical resolution, increased length of hospital stay, and an increased risk of mortality. Moreover, it is becoming more frequent for isolates recovered from patients to possess multiple resistance factors (e.g., extended-spectrum beta-lactamases [ESBLs], vancomycin-resistant enterococci [VRE]). Therefore, when selecting empiric antimicrobial therapy, the physician must consider the likelihood of encountering one of these difficult-to-treat isolates and select an agent or agents with anticipated activity against such organisms. Here, we discuss the merits and limitations of empiric therapy for nosocomial intra-abdominal infections, review the current guidelines for treatment, and discuss the therapeutic options currently available.

Therapeutic targets: progress of their exploration and investigation of their characteristics

Modern drug discovery is primarily based on the search and subsequent testing of drug candidates acting on a preselected therapeutic target. Progress in genomics, protein structure, proteomics, and disease mechanisms has led to a growing interest in and effort for finding new targets and more effective exploration of existing targets. The number of reported targets of marketed and investigational drugs has significantly increased in the past 8 years. There are 1535 targets collected in the therapeutic target database compared with approximately 500 targets reported in a 1996 review. Knowledge of these targets is helpful for molecular dissection of the mechanism of action of drugs and for predicting features that guide new drug design and the search for new targets. This article summarizes the progress of target exploration and investigates the characteristics of the currently explored targets to analyze their sequence, structure, family representation, pathway association, tissue distribution, and genome location features for finding clues useful for searching for new targets. Possible "rules" to guide the search for druggable proteins and the feasibility of using a statistical learning method for predicting druggable proteins directly from their sequences are discussed.

The historical delivery of antibiotics from microbial natural products—Can history repeat?

Microbial natural products are the origin of most of the antibiotics on the market today. However, research in antibiotics and natural products has declined significantly during the last decade as a consequence of diverse factors, among which the lack of interest of industry in the field and the strong competition from collections of synthetic compounds as source of drug leads. As a consequence, there is an alarming scarcity of new antibiotic classes in the pipelines of the pharmaceutical industry. Still, microbial natural products remain the most promising source of novel antibiotics, although new approaches are required to improve the efficiency of the discovery process. The impact of microbial biodiversity, the influence of growth conditions on the production of secondary metabolites, the choice of the best approach at the screening step and the challenges faced during the isolation and identification of the active compounds are examined in this review as the critical factors contributing to success in the effort of antibiotic discovery from microbial natural products.

Treatment of intra-abdominal and skin and soft tissue infections: The role of the glycylcyclines

The need for new, effective agents to treat multidrug-resistant infections continues to grow as more and more bacteria develop resistance that may result in clinical therapeutic failure. This is particularly true for common surgical infections, such as complicated intra-abdominal infections, which frequently involve multiple pathogens, making therapy with a broad-spectrum antibiotic an important treatment intervention, and also for complicated skin infections, which often involve methicillin-resistant Staphylococcus aureus (MRSA) and vancomycin-resistant enterococci (VRE). With treatment options limited, it has become critical to identify antibiotics with novel mechanisms of activity. Several new drugs have emerged as possible therapeutic alternatives: linezolid, quinupristin-dalfopristin and most recently daptomycin have all been FDA-approved for the treatment of skin and skin structure infections. This review examines the potential role of a new class of investigational agents, the glycylcyclines, also recently FDA-approved and currently under review for European licensing, in the treatment of complicated skin infections and intra-abdominal infections. Tigecycline, the first of the glycylcyclines, has shown excellent activity in Phase III studies of these infections, achieving clinical success rates ranging from 70% to 91%. Furthermore, it has a good safety profile, suggesting it will be a clinical useful addition to current therapeutic options for the treatment of complicated skin infections and intra-abdominal infections.

Management of serious nosocomial bacterial infections: do current therapeutic options meet the need?

Hospital-acquired bacterial infections pose a formidable challenge for healthcare providers, as patients often need to be treated empirically, at least initially, although delay of appropriate initial antimicrobial therapy is known to increase morbidity significantly and to increase mortality among affected patients. This elevated risk is compounded by the presence of antibiotic-resistant bacteria, including methicillin-resistant Staphylococcus aureus (MRSA), vancomycin-resistant enterococci (VRE), extended-spectrum beta-lactamase-producing Enterobacteriaceae, Escherichia coli and Klebsiella pneumoniae. Prompt initiation of treatment with an appropriate antimicrobial agent that is active against both Gram-positive and Gram-negative organisms is prudent for patients with nosocomial infections. As the continued usefulness of vancomycin comes into question, the number of alternative agents that provide efficacy equal to that of vancomycin remains limited. The development of novel and effective alternative agents, such as tigecycline, is therefore important.

Tigecycline: clinical evidence and formulary positioning

Tigecycline, is a novel broad-spectrum glycylcycline antibiotic, which has activity against a broad range of Gram-positive, Gram-negative, atypical, anaerobic and antibiotic-resistant bacteria. This includes activity against MRSA, VRE and penicillin resistant Streptococcus pneumoniae. Whilst exhibiting antibacterial activities typical of earlier tetracyclines, it has more potent activity against tetracycline-resistant organisms. Although a bacteriostatic compound in vitro, its effectiveness in clinical trials suggests that traditional laboratory thinking about using bacteriostatic drugs in serious infections needs to be revised. Unlike existing tetracyclines, tigecycline is only available as an intravenous preparation, is administered twice daily although its long half life and post-antibiotic effect may make once daily dosing possible, appears to have good tissue penetration (e.g. skin) and requires no adjustment in the presence of renal or hepatic diseases. It is efficacious in complicated skin and soft tissue infections and in intra-abdominal infections. In three trials, it was well tolerated despite increased frequency of nausea and vomiting. In the light of these early clinical data and the likelihood that this agent will become available for clinical use within the next 12-24 months, this review aims to summarise the key clinical data and potential formulary considerations for the future use of this agent, subject to further clinical trials and publication of clinical human data.

Synthesis and in vitro antimicrobial activities of 2-hydroxy-6-methyl-7-(arylamino)-1,7-dihydropurin-8-ones

A number of 2-hydroxy-6-methyl-7-(arylamino)-1,7-dihydropurin-8-ones have been synthesized. 3-Oxo-2-(arylhydrazono)butyric acid ethyl ester were acetylated and treated with triethyl amine and formamide in presence of 1,4-dioxane to yield N-(5-acetyl-4-ethoxy-2-oxo-2,5-dihydro-imidazol-1-yl)-N-arylacetamide, which on refluxation with urea and freshly prepared sodium ethoxide yielded the title compound. All the newly synthesized compounds have been characterized by spectroscopic and elemental analysis data. The synthesized compounds were screened against a representative panel of susceptible and resistant Gram-positive and Gram-negative bacteria using a standard antibiotic drug purinthol as control. Quantitative structure-activity relationship has also been interpreted in terms of correlation of biological activity with molecular refractive index parameters (M(R)) and Hammett substituent constant (sigma).

New Benzylidenethiazolidinediones as Antibacterial Agents

A novel benzylidenethiazolidinedione has been discovered with antimicrobial activity. Here, we present the results of a structure-activity study on this compound with respect to its antimicrobial activity.

A new TEM-derived extended-spectrum beta-lactamase (TEM-91) with an R164C substitution at the omega-loop confers ceftazidime resistance

A new plasmid-mediated TEM-derived extended-spectrum beta-lactamase, TEM-91, was identified in a ceftazidime-resistant (MIC, >128 microg per ml) Escherichia coli strain isolated in 1996 in Japan. TEM-91 has three amino acid substitutions, R164C, M184T, and E240K, compared with TEM-1 penicillinase. The isoelectric point (pI), K(m), and k(cat) of TEM-91 for ceftazidime were 5.7, 179 microM, and 29.0 s(-1), respectively. The K(i) of clavulanic acid for ceftazidime hydrolysis was 30.3 nM.

Histidine kinases as targets for new antimicrobial agents

The emergence and spread of hospital acquired multi drug resistant bacteria present a need for new antibiotics with innovative mode of action. Advances in molecular microbiology and genomics have led to the identification of numerous bacterial genes coding for proteins that could potentially serve as targets for antibacterial compounds. Histidine kinase promoted two-component systems are extremely common in bacteria and play an important role in essential signal transduction for adapting to bacterial stress. Since signal transduction in mammals occurs by a different mechanism, inhibition of histidine kinases could be a potential target for antimicrobial agents. This review will summarize our current knowledge of the structure and function of histidine kinase and the development of antibiotics with a new mode of action: targeting histidine kinase promoted signal transduction and its subsequent regulation of gene expression system.

The use of linezolid in the treatment of vancomycin-resistant enterococcal septicaemia in two patients with burn injuries

Vancomycin-resistant enterococci (VRE) are multi-resistant micro-organisms that have emerged as important nosocomial pathogens during the last decade. Emergence of this organism has been blamed mainly on the increased and inappropriate use of antibiotics, in particular, the cephalosporins and the glycopeptide, vancomycin. Burns patients are highly vulnerable to acquiring VRE infections, being both debilitated and immunocompromised, and often receiving antibiotics that further diminish their intrinsic microbial flora. We report on two patients with large burn injuries who acquired vancomycin-resistant enterococcal septicaemia during their in-patient stay. Both patients were successfully treated using the antibiotic, linezolid. Linezolid is the first in a new class of antibiotics known as the oxazolidinones whose mode of action inhibits early bacterial protein synthesis. Linezolid has a spectrum of activity against Gram-positive micro-organisms including methicillin-resistant Staphylococcus aureus (MRSA) and VRE, and can provide a useful treatment alternative to the glycopeptides.