A new antibiotic kills pathogens without detectable resistance

Carbohydrate scaffolds as glycosyltransferase inhibitors with in vivo antibacterial activity

The rapid rise of multi-drug-resistant bacteria is a global healthcare crisis, and new antibiotics are urgently required, especially those with modes of action that have low-resistance potential. One promising lead is the liposaccharide antibiotic moenomycin that inhibits bacterial glycosyltransferases, which are essential for peptidoglycan polymerization, while displaying a low rate of resistance. Unfortunately, the lipophilicity of moenomycin leads to unfavourable pharmacokinetic properties that render it unsuitable for systemic administration. In this study, we show that using moenomycin and other glycosyltransferase inhibitors as templates, we were able to synthesize compound libraries based on novel pyranose scaffold chemistry, with moenomycin-like activity, but with improved drug-like properties. The novel compounds exhibit in vitro inhibition comparable to moenomycin, with low toxicity and good efficacy in several in vivo models of infection. This approach based on non-planar carbohydrate scaffolds provides a new opportunity to develop new antibiotics with low propensity for resistance induction.

Effective Antibiofilm Polyketides against Staphylococcus aureus from the Pyranonaphthoquinone Biosynthetic Pathways of Streptomyces Species

Streptomyces bacteria are renowned for their ability to produce bioactive secondary metabolites. Recently, synthetic biology has enabled the production of intermediates and shunt products, which may have altered biological activities compared to the end products of the pathways. Here, we have evaluated the potential of recently isolated alnumycins and other closely related pyranonaphthoquinone (PNQ) polyketides against Staphylococcus aureus biofilms. The antimicrobial potency of the compounds against planktonic cells and biofilms was determined by redox dye-based viability staining, and the antibiofilm efficacy of the compounds was confirmed by viable counting. A novel antistaphylococcal polyketide, alnumycin D, was identified. Unexpectedly, the C-ribosylated pathway shunt product alnumycin D was more active against planktonic and biofilm cells than the pathway end product alnumycin A, where a ribose unit has been converted into a dioxane moiety. The evaluation of the antibiofilm potential of other alnumycins revealed that the presence of the ribose moiety in pyranose form is essential for high activity against preformed biofilms. Furthermore, the antibiofilm potential of other closely related PNQ polyketides was examined. Based on their previously reported activity against planktonic S. aureus cells, granaticin B, kalafungin, and medermycin were also selected for testing, and among them, granaticin B was found to be the most potent against preformed biofilms. The most active antibiofilm PNQs, alnumycin D and granaticin B, share several structural features that may be important for their antibiofilm activity. They are uncharged, glycosylated, and also contain a similar oxygenation pattern of the lateral naphthoquinone ring. These findings highlight the potential of antibiotic biosynthetic pathways as a source of effective antibiofilm compounds.

Chemically Induced Changes to Membrane Permeability in Living Cells Probed with Nonlinear Light Scattering

Second-harmonic light scattering (SHS) permits characterization of membrane-specific molecular transport in living cells. Herein, we demonstrate the use of time-resolved SHS for quantifying chemically induced enhancements in membrane permeability. As proof of concept, we examine the enhanced permeability of the cytoplasmic membrane in living Escherichia coli following addition of extracellular adenosine triphosphate (ATPe). The transport rate of the hydrophobic cation, malachite green, increases nearly an order of magnitude following addition of 0.1 mM ATPe. The absence of an ATPe-enhanced permeability in liposomes strongly suggests the induced effect is protein-mediated. The utility of SHS for elucidating the mechanism of action of antimicrobials is discussed.

Semisynthetic Lipopeptides Derived from Nisin Display Antibacterial Activity and Lipid II Binding on Par with That of the Parent Compound

The lipid II-binding N-terminus of nisin, comprising the so-called A/B ring system, was synthetically modified to provide antibacterially active and proteolytically stable derivatives. A variety of lipids were coupled to the C-terminus of the nisin A/B ring system to generate semisynthetic constructs that display potent inhibition of bacterial growth, with activities approaching that of nisin itself. Most notable was the activity observed against clinically relevant bacterial strains including MRSA and VRE. Experiments with membrane models indicate that these constructs operate via a lipid II-mediated mode of action without causing pore formation. A lipid II-dependent mechanism of action is further supported by antagonization assays wherein the addition of lipid II was found to effectively block the antibacterial activity of the nisin-derived lipopeptides.

The Molecular Epidemiology and Genetic Environment of Carbapenemases Detected in Africa

Research articles describing carbapenemases and their genetic environments in Gram-negative bacteria were reviewed to determine the molecular epidemiology of carbapenemases in Africa. The emergence of resistance to the carbapenems, the last resort antibiotic for difficult to treat bacterial infections, affords clinicians few therapeutic options, with a resulting increase in morbidities, mortalities, and healthcare costs. However, the molecular epidemiology of carbapenemases throughout Africa is less described. Research articles and conference proceedings describing the genetic environment and molecular epidemiology of carbapenemases in Africa were retrieved from Google Scholar, Scifinder, Pubmed, Web of Science, and Science Direct databases. Predominant carbapenemase genes so far described in Africa include the blaOXA-48 type, blaIMP, blaVIM, and blaNDM in Acinetobacter baumannii, Klebsiella pneumoniae, Enterobacter cloacae, Citrobacter spp., and Escherichia coli carried on various plasmid types and sizes, transposons, and integrons. Class D and class B carbapenemases, mainly prevalent in A. baumannii, K. pneumoniae, E. cloacae, Citrobacter spp., and E. coli were the commonest carbapenemases. Carbapenemases are mainly reported in North and South Africa as under-resourced laboratories, lack of awareness and funding preclude the detection and reporting of carbapenemase-mediated resistance. Consequently, the true molecular epidemiology of carbapenemases and their genetic environment in Africa is still unknown.

Helping Chemists Discover New Antibiotics

The world is facing a crisis in treating infectious diseases, with a scarcity of new antibiotics in development to treat the growing threat of drug-resistant "superbugs". We need new strategies to reinvigorate the antibiotic pipeline. In this Viewpoint we discuss one such approach, encouraging the community of synthetic chemists to participate in testing chemical diversity from their laboratories for antimicrobial potential. CO-ADD, the Community for Open Antimicrobial Drug Discovery, offers free screening against five bacteria and two fungi with follow up hit confirmation and validation, all with no strings attached.

What was old is new again: using the host response to diagnose infectious disease

A century of advances in infectious disease diagnosis and treatment changed the face of medicine. However, challenges continue to develop including multi-drug resistance, globalization that increases pandemic risks and high mortality from severe infections. These challenges can be mitigated through improved diagnostics, focusing on both pathogen discovery and the host response. Here, we review how 'omics' technologies improve sepsis diagnosis, early pathogen identification and personalize therapy. Such host response diagnostics are possible due to the confluence of advanced laboratory techniques (e.g., transcriptomics, metabolomics, proteomics) along with advanced mathematical modeling such as machine learning techniques. The road ahead is promising, but obstacles remain before the impact of such advanced diagnostic modalities is felt at the bedside.

Individuality, phenotypic differentiation, dormancy and 'persistence' in culturable bacterial systems: commonalities shared by environmental, laboratory, and clinical microbiology

For bacteria, replication mainly involves growth by binary fission. However, in a very great many natural environments there are examples of phenotypically dormant, non-growing cells that do not replicate immediately and that are phenotypically 'nonculturable' on media that normally admit their growth. They thereby evade detection by conventional culture-based methods. Such dormant cells may also be observed in laboratory cultures and in clinical microbiology. They are usually more tolerant to stresses such as antibiotics, and in clinical microbiology they are typically referred to as 'persisters'. Bacterial cultures necessarily share a great deal of relatedness, and inclusive fitness theory implies that there are conceptual evolutionary advantages in trading a variation in growth rate against its mean, equivalent to hedging one's bets. There is much evidence that bacteria exploit this strategy widely. We here bring together data that show the commonality of these phenomena across environmental, laboratory and clinical microbiology. Considerable evidence, using methods similar to those common in environmental microbiology, now suggests that many supposedly non-communicable, chronic and inflammatory diseases are exacerbated (if not indeed largely caused) by the presence of dormant or persistent bacteria (the ability of whose components to cause inflammation is well known). This dormancy (and resuscitation therefrom) often reflects the extent of the availability of free iron. Together, these phenomena can provide a ready explanation for the continuing inflammation common to such chronic diseases and its correlation with iron dysregulation. This implies that measures designed to assess and to inhibit or remove such organisms (or their access to iron) might be of much therapeutic benefit.

New OprM structure highlighting the nature of the N-terminal anchor

Among the different mechanisms used by bacteria to resist antibiotics, active efflux plays a major role. In Gram-negative bacteria, active efflux is carried out by tripartite efflux pumps that form a macromolecular assembly spanning both membranes of the cellular wall. At the outer membrane level, a well-conserved outer membrane factor (OMF) protein acts as an exit duct, but its sequence varies greatly among different species. The OMFs share a similar tri-dimensional structure that includes a beta-barrel pore domain that stabilizes the channel within the membrane. In addition, OMFs are often subjected to different N-terminal post-translational modifications (PTMs), such as an acylation with a lipid. The role of additional N-terminal anchors is all the more intriguing since it is not always required among the OMFs family. Understanding this optional PTM could open new research lines in the field of antibiotics resistance. In Escherichia coli, it has been shown that CusC is modified with a tri-acylated lipid, whereas TolC does not show any modification. In the case of OprM from Pseudomonas aeruginosa, the N-terminal modification remains a matter of debate, therefore, we used several approaches to investigate this issue. As definitive evidence, we present a new X-ray structure at 3.8 Å resolution that was solved in a new space group, making it possible to model the N-terminal residue as a palmitoylated cysteine.

Individuality, phenotypic differentiation, dormancy and 'persistence' in culturable bacterial systems: commonalities shared by environmental, laboratory, and clinical microbiology

For bacteria, replication mainly involves growth by binary fission. However, in a very great many natural environments there are examples of phenotypically dormant, non-growing cells that do not replicate immediately and that are phenotypically 'nonculturable' on media that normally admit their growth. They thereby evade detection by conventional culture-based methods. Such dormant cells may also be observed in laboratory cultures and in clinical microbiology. They are usually more tolerant to stresses such as antibiotics, and in clinical microbiology they are typically referred to as 'persisters'. Bacterial cultures necessarily share a great deal of relatedness, and inclusive fitness theory implies that there are conceptual evolutionary advantages in trading a variation in growth rate against its mean, equivalent to hedging one's bets. There is much evidence that bacteria exploit this strategy widely. We here bring together data that show the commonality of these phenomena across environmental, laboratory and clinical microbiology. Considerable evidence, using methods similar to those common in environmental microbiology, now suggests that many supposedly non-communicable, chronic and inflammatory diseases are exacerbated (if not indeed largely caused) by the presence of dormant or persistent bacteria (the ability of whose components to cause inflammation is well known). This dormancy (and resuscitation therefrom) often reflects the extent of the availability of free iron. Together, these phenomena can provide a ready explanation for the continuing inflammation common to such chronic diseases and its correlation with iron dysregulation. This implies that measures designed to assess and to inhibit or remove such organisms (or their access to iron) might be of much therapeutic benefit.

Biotechnological applications of functional metagenomics in the food and pharmaceutical industries

Microorganisms are found throughout nature, thriving in a vast range of environmental conditions. The majority of them are unculturable or difficult to culture by traditional methods. Metagenomics enables the study of all microorganisms, regardless of whether they can be cultured or not, through the analysis of genomic data obtained directly from an environmental sample, providing knowledge of the species present, and allowing the extraction of information regarding the functionality of microbial communities in their natural habitat. Function-based screenings, following the cloning and expression of metagenomic DNA in a heterologous host, can be applied to the discovery of novel proteins of industrial interest encoded by the genes of previously inaccessible microorganisms. Functional metagenomics has considerable potential in the food and pharmaceutical industries, where it can, for instance, aid (i) the identification of enzymes with desirable technological properties, capable of catalyzing novel reactions or replacing existing chemically synthesized catalysts which may be difficult or expensive to produce, and able to work under a wide range of environmental conditions encountered in food and pharmaceutical processing cycles including extreme conditions of temperature, pH, osmolarity, etc; (ii) the discovery of novel bioactives including antimicrobials active against microorganisms of concern both in food and medical settings; (iii) the investigation of industrial and societal issues such as antibiotic resistance development. This review article summarizes the state-of-the-art functional metagenomic methods available and discusses the potential of functional metagenomic approaches to mine as yet unexplored environments to discover novel genes with biotechnological application in the food and pharmaceutical industries.

Discovery of microbial natural products by activation of silent biosynthetic gene clusters

Microorganisms produce a wealth of structurally diverse specialized metabolites with a remarkable range of biological activities and a wide variety of applications in medicine and agriculture, such as the treatment of infectious diseases and cancer, and the prevention of crop damage. Genomics has revealed that many microorganisms have far greater potential to produce specialized metabolites than was thought from classic bioactivity screens; however, realizing this potential has been hampered by the fact that many specialized metabolite biosynthetic gene clusters (BGCs) are not expressed in laboratory cultures. In this Review, we discuss the strategies that have been developed in bacteria and fungi to identify and induce the expression of such silent BGCs, and we briefly summarize methods for the isolation and structural characterization of their metabolic products.

The global challenge of new classes of antibacterial agents: an industry perspective

With rising antibiotic resistance and the fear of returning to the pre-penicillin era, incentives are being provided for developing novel antibiotics. The hurdles faced by antibiotic developers include the difficulty in discovering novel chemicals that have selectivity and the increased regulatory scrutiny for safety and efficacy. Furthermore, the demonstration of superiority is essential in order to rationalize pricing and to assure a return on investment. Suggestions are provided to overcome each of these hurdles in order to prevent the antibiotic pipeline from running dry.

Rapid synthesis and antimicrobial activity of novel 4-oxazolidinone heterocycles

The synoxazolidinone family of marine natural products bear an unusual 4-oxazolidinone heterocyclic core and promising antimicrobial activity against several strains of pathogenic bacteria. As part of our research program directed at the synthesis and chemical biology of this family of natural products we have developed a one-step method for the generation of variously substituted 4-oxazolidinone scaffolds from readily available materials. These studies revealed the importance of an electron deficient aromatic ring for antimicrobial activity and serve as the basis for future SAR studies around the 4-oxazolidinone core.

Discovery of new protein families and functions: new challenges in functional metagenomics for biotechnologies and microbial ecology

The rapid expansion of new sequencing technologies has enabled large-scale functional exploration of numerous microbial ecosystems, by establishing catalogs of functional genes and by comparing their prevalence in various microbiota. However, sequence similarity does not necessarily reflect functional conservation, since just a few modifications in a gene sequence can have a strong impact on the activity and the specificity of the corresponding enzyme or the recognition for a sensor. Similarly, some microorganisms harbor certain identified functions yet do not have the expected related genes in their genome. Finally, there are simply too many protein families whose function is not yet known, even though they are highly abundant in certain ecosystems. In this context, the discovery of new protein functions, using either sequence-based or activity-based approaches, is of crucial importance for the discovery of new enzymes and for improving the quality of annotation in public databases. This paper lists and explores the latest advances in this field, along with the challenges to be addressed, particularly where microfluidic technologies are concerned.

Targets for Combating the Evolution of Acquired Antibiotic Resistance

Bacteria possess a remarkable ability to rapidly adapt and evolve in response to antibiotics. Acquired antibiotic resistance can arise by multiple mechanisms but commonly involves altering the target site of the drug, enzymatically inactivating the drug, or preventing the drug from accessing its target. These mechanisms involve new genetic changes in the pathogen leading to heritable resistance. This recognition underscores the importance of understanding how such genetic changes can arise. Here, we review recent advances in our understanding of the processes that contribute to the evolution of antibiotic resistance, with a particular focus on hypermutation mediated by the SOS pathway and horizontal gene transfer. We explore the molecular mechanisms involved in acquired resistance and discuss their viability as potential targets. We propose that additional studies into these adaptive mechanisms not only can provide insights into evolution but also can offer a strategy for potentiating our current antibiotic arsenal.

Expanding the chemical space for natural products by Aspergillus-Streptomyces co-cultivation and biotransformation

Actinomycetes and filamentous fungi produce a wide range of bioactive compounds, with applications as antimicrobials, anticancer agents or agrochemicals. Their genomes contain a far larger number of gene clusters for natural products than originally anticipated, and novel approaches are required to exploit this potential reservoir of new drugs. Here, we show that co-cultivation of the filamentous model microbes Streptomyces coelicolor and Aspergillus niger has a major impact on their secondary metabolism. NMR-based metabolomics combined with multivariate data analysis revealed several compounds that correlated specifically to co-cultures, including the cyclic dipeptide cyclo(Phe-Phe) and 2-hydroxyphenylacetic acid, both of which were produced by A. niger in response to S. coelicolor. Furthermore, biotransformation studies with o-coumaric acid and caffeic acid resulted in the production of the novel compounds (E)-2-(3-hydroxyprop-1-en-1-yl)-phenol and (2E,4E)-3-(2-carboxy-1-hydroxyethyl)-2,4-hexadienedioxic acid, respectively. This highlights the utility of microbial co-cultivation combined with NMR-based metabolomics as an efficient pipeline for the discovery of novel natural products.

Nontoxic antimicrobials that evade drug resistance

Drugs that act more promiscuously provide fewer routes for the emergence of resistant mutants. But this benefit often comes at the cost of serious off-target and dose-limiting toxicities. The classic example is the antifungal amphotericin B (AmB), which has evaded resistance for more than half a century. We report dramatically less toxic amphotericins that nevertheless evade resistance. They are scalably accessed in just three steps from the natural product, and bind their target (the fungal sterol, ergosterol) with far greater selectivity than AmB. Hence, they are less toxic and far more effective in a mouse model of systemic candidiasis. Surprisingly, exhaustive efforts to select for mutants resistant to these more selective compounds revealed that they are just as impervious to resistance as AmB. Thus, highly selective cytocidal action and the evasion of resistance are not mutually exclusive, suggesting practical routes to the discovery of less toxic, resistance-evasive therapies.

An update on new methods to synthesize cyclotetrapeptides

Cyclotetrapeptides are important bioactive lead drug molecules that display a wide spectrum of pharmacological activities. However, the synthesis of cyclotetrapeptides from their linear precursors is challenging due to the highly constrained conformation required for cyclisation, thus hampering their progress to a clinical setting. This review provides an account of the reported methods used for the synthesis of cyclotetrapeptides.

The potential impact of coinfection on antimicrobial chemotherapy and drug resistance

Across a range of pathogens, resistance to chemotherapy is a growing problem in both public health and animal health. Despite the ubiquity of coinfection, and its potential effects on within-host biology, the role played by coinfecting pathogens on the evolution of resistance and efficacy of antimicrobial chemotherapy is rarely considered. In this review, we provide an overview of the mechanisms of interaction of coinfecting pathogens, ranging from immune modulation and resource modulation, to drug interactions. We discuss their potential implications for the evolution of resistance, providing evidence in the rare cases where it is available. Overall, our review indicates that the impact of coinfection has the potential to be considerable, suggesting that this should be taken into account when designing antimicrobial drug treatments.

Borrelia burgdorferi, the Causative Agent of Lyme Disease, Forms Drug-Tolerant Persister Cells

Borrelia burgdorferi is the causative agent of Lyme disease, which affects an estimated 300,000 people annually in the United States. When treated early, the disease usually resolves, but when left untreated, it can result in symptoms such as arthritis and encephalopathy. Treatment of the late-stage disease may require multiple courses of antibiotic therapy. Given that antibiotic resistance has not been observed for B. burgdorferi, the reason for the recalcitrance of late-stage disease to antibiotics is unclear. In other chronic infections, the presence of drug-tolerant persisters has been linked to recalcitrance of the disease. In this study, we examined the ability of B. burgdorferi to form persisters. Killing growing cultures of B. burgdorferi with antibiotics used to treat the disease was distinctly biphasic, with a small subpopulation of surviving cells. Upon regrowth, these cells formed a new subpopulation of antibiotic-tolerant cells, indicating that these are persisters rather than resistant mutants. The level of persisters increased sharply as the culture transitioned from the exponential to stationary phase. Combinations of antibiotics did not improve killing. Daptomycin, a membrane-active bactericidal antibiotic, killed stationary-phase cells but not persisters. Mitomycin C, an anticancer agent that forms adducts with DNA, killed persisters and eradicated growing and stationary cultures of B. burgdorferi. Finally, we examined the ability of pulse dosing an antibiotic to eliminate persisters. After addition of ceftriaxone, the antibiotic was washed away, surviving persisters were allowed to resuscitate, and the antibiotic was added again. Four pulse doses of ceftriaxone killed persisters, eradicating all live bacteria in the culture.

Designing drugs that overcome antibacterial resistance: where do we stand and what should we do?

INTRODUCTION

In recent years, infections caused by multidrug-resistant bacterial pathogens have become a huge issue to public healthcare systems. Indeed, the misuse of antibiotics has led to, over the past 30 years, the emergence of a number of resistant bacterial strains including Staphylococcus aureus, Neisseria gonorrhoeae, Escherichia coli and Mycobacterium tuberculosis. Unfortunately, efforts to produce new antibiotics have not been sufficient to cope with the emergence of these new antibiotic-resistant (AR) strains.

AREAS COVERED

There is an urgent need to invent and employ unconventional strategies for antimicrobial drug development to tackle the rising global threats imposed by the spread of antimicrobial resistance. Herein, the authors discuss these novel design strategies and provide their expert perspective on the subject.

EXPERT OPINION

To deal with the growing threat of AR, it is important to cut down the use of antibiotics to the very minimum to diminish the risk of unknown drug-resistant bacteria and increase antibacterial vaccination programs. Furthermore, it is important to develop new classes of antibiotics that can deal with multidrug-resistant bacterial pathogens.

Antitumor and antimicrobial activity of some cyclic tetrapeptides and tripeptides derived from marine bacteria

Marine derived cyclo(Gly-l-Ser-l-Pro-l-Glu) was selected as a lead to evaluate antitumor-antibiotic activity. Histidine was chosen to replace the serine residue to form cyclo(Gly-l-His-l-Pro-l-Glu). Cyclic tetrapeptides (CtetPs) were then synthesized using a solution phase method, and subjected to antitumor and antibiotic assays. The benzyl group protected CtetPs derivatives, showed better activity against antibiotic-resistant Staphylococcus aureus in the range of 60–120 μM. Benzyl group protected CtetPs 3 and 4, exhibited antitumor activity against several cell lines at a concentration of 80–108 μM. However, shortening the size of the ring to the cyclic tripeptide (CtriP) scaffold, cyclo(Gly-l-Ser-l-Pro), cyclo(Ser-l-Pro-l-Glu) and their analogues showed no antibiotic or antitumor activity. This phenomenon can be explained from their backbone structures.

Toward a new focus in antibiotic and drug discovery from the Streptomyces arsenal

Emergence of antibiotic resistant pathogens is changing the way scientists look for new antibiotic compounds. This race against the increased prevalence of multi-resistant strains makes it necessary to expedite the search for new compounds with antibiotic activity and to increase the production of the known. Here, we review a variety of new scientific approaches aiming to enhance antibiotic production in Streptomyces. These include: (i) elucidation of the signals that trigger the antibiotic biosynthetic pathways to improve culture media, (ii) bacterial hormone studies aiming to reproduce intra and interspecific communications resulting in antibiotic burst, (iii) co-cultures to mimic competition-collaboration scenarios in nature, and (iv) the very recent in situ search for antibiotics that might be applied in Streptomyces natural habitats. These new research strategies combined with new analytical and molecular techniques should accelerate the discovery process when the urgency for new compounds is higher than ever.

Engineering a nanostructured "super surface" with superhydrophobic and superkilling properties

We present a nanostructured "super surface" fabricated using a simple recipe based on deep reactive ion etching of a silicon wafer. The topography of the surface is inspired by the surface topographical features of dragonfly wings. The super surface is comprised of nanopillars 4 μm in height and 220 nm in diameter with random inter-pillar spacing. The surface exhibited superhydrophobicity with a static water contact angle of 154.0° and contact angle hysteresis of 8.3°. Bacterial studies revealed the bactericidal property of the surface against both gram negative (Escherichia coli) and gram positive (Staphylococcus aureus) strains through mechanical rupture of the cells by the sharp nanopillars. The cell viability on these nanostructured surfaces was nearly six-fold lower than on the unmodified silicon wafer. The nanostructured surface also killed mammalian cells (mouse osteoblasts) through mechanical rupture of the cell membrane. Thus, such nanostructured super surfaces could find applications for designing self-cleaning and anti-bacterial surfaces in diverse applications such as microfluidics, surgical instruments, pipelines and food packaging.

The dormant blood microbiome in chronic, inflammatory diseases

Blood in healthy organisms is seen as a ‘sterile’ environment: it lacks proliferating microbes. Dormant or not-immediately-culturable forms are not absent, however, as intracellular dormancy is well established. We highlight here that a great many pathogens can survive in blood and inside erythrocytes. ‘Non-culturability’, reflected by discrepancies between plate counts and total counts, is commonplace in environmental microbiology. It is overcome by improved culturing methods, and we asked how common this would be in blood. A number of recent, sequence-based and ultramicroscopic studies have uncovered an authentic blood microbiome in a number of non-communicable diseases. The chief origin of these microbes is the gut microbiome (especially when it shifts composition to a pathogenic state, known as ‘dysbiosis’). Another source is microbes translocated from the oral cavity. ‘Dysbiosis’ is also used to describe translocation of cells into blood or other tissues. To avoid ambiguity, we here use the term ‘atopobiosis’ for microbes that appear in places other than their normal location. Atopobiosis may contribute to the dynamics of a variety of inflammatory diseases. Overall, it seems that many more chronic, non-communicable, inflammatory diseases may have a microbial component than are presently considered, and may be treatable using bactericidal antibiotics or vaccines.

Atopobiosis of microbes (the term describing microbes that appear in places other than where they should be), as well as the products of their metabolism, seems to correlate with, and may contribute to, the dynamics of a variety of inflammatory diseases.

The antibiotic resistance crisis: part 2: management strategies and new agents

Controlling antibiotic-resistant bacteria calls for widespread adoption of antibiotic stewardship programs; better diagnosis, tracking and prescribing practices; optimized therapeutic regimens; prevention of infection transmission-and new drugs.

Reconstructing rare soil microbial genomes using in situ enrichments and metagenomics

Despite extensive direct sequencing efforts and advanced analytical tools, reconstructing microbial genomes from soil using metagenomics have been challenging due to the tremendous diversity and relatively uniform distribution of genomes found in this system. Here we used enrichment techniques in an attempt to decrease the complexity of a soil microbiome prior to sequencing by submitting it to a range of physical and chemical stresses in 23 separate microcosms for 4 months. The metagenomic analysis of these microcosms at the end of the treatment yielded 540 Mb of assembly using standard de novo assembly techniques (a total of 559,555 genes and 29,176 functions), from which we could recover novel bacterial genomes, plasmids and phages. The recovered genomes belonged to Leifsonia (n = 2), Rhodanobacter (n = 5), Acidobacteria (n = 2), Sporolactobacillus (n = 2, novel nitrogen fixing taxon), Ktedonobacter (n = 1, second representative of the family Ktedonobacteraceae), Streptomyces (n = 3, novel polyketide synthase modules), and Burkholderia (n = 2, includes mega-plasmids conferring mercury resistance). Assembled genomes averaged to 5.9 Mb, with relative abundances ranging from rare (<0.0001%) to relatively abundant (>0.01%) in the original soil microbiome. Furthermore, we detected them in samples collected from geographically distant locations, particularly more in temperate soils compared to samples originating from high-latitude soils and deserts. To the best of our knowledge, this study is the first successful attempt to assemble multiple bacterial genomes directly from a soil sample. Our findings demonstrate that developing pertinent enrichment conditions can stimulate environmental genomic discoveries that would have been impossible to achieve with canonical approaches that focus solely upon post-sequencing data treatment.

Tuning the production of variable length, fluorescent polyisoprenoids using surfactant-controlled enzymatic synthesis

Bactoprenyl diphosphate (BPP), a two-E eight-Z configuration C55 isoprenoid, serves as a critical anchor for the biosynthesis of complex glycans central to bacterial survival and pathogenesis. BPP is formed by the polymerase undecaprenyl pyrophosphate synthase (UppS), which catalyzes the elongation of a single farnesyl diphosphate (FPP) with eight Z-configuration isoprene units from eight isopentenyl diphosphates. In vitro analysis of UppS and other polyprenyl diphosphate synthases requires the addition of a surfactant such as Triton X-100 to stimulate the release of the hydrophobic product from the enzyme for effective and efficient turnover. Here using a fluorescent 2-nitrileanilinogeranyl diphosphate analogue of FPP, we have found that a wide range of surfactants can stimulate release of product from UppS and that the structure of the surfactant has a major impact on the lengths of products produced by the protein. Of particular importance, shorter chain surfactants promote the release of isoprenoids with four to six Z-configuration isoprene additions, while larger chain surfactants promote the formation of natural isoprenoid lengths (8Z) and larger. We have found that the product chain lengths can be readily controlled and coarsely tuned by adjusting surfactant identity, concentration, and reaction time. We have also found that binary mixtures of just two surfactants can be used to fine-tune isoprenoid lengths. The surfactant effects discovered do not appear to be significantly altered with an alternative isoprenoid substrate. However, the surfactant effects do appear to be dependent on differences in UppS between bacterial species. This work provides new insights into surfactant effects in enzymology and highlights how these effects can be leveraged for the chemoenzymatic synthesis of otherwise difficult to obtain glycan biosynthesis probes. This work also provides key reagents for the systematic analysis of structure-activity relationships between glycan biosynthesis enzymes and isoprenoid structure.

Thinking globally, acting locally: harnessing the immune system to deal with recalcitrant pathogens

Traditional approaches to harnessing the immune system to confront infectious diseases depend on vaccines, which have generally proven highly effective, but for many infections these either are not available or are of limited effectiveness. Although antibiotic therapy has been extremely successful in reducing the burden of bacterial disease, the emergence of resistance among several important pathogens threatens to undermine this accomplishment, and despite some successes chemotherapeutic treatments for viral, fungal, and parasitic infections are more limited. Understanding the mechanisms whereby pathogens manipulate the immune system to favor their survival, or exploit weaknesses in host immunity, can lead to novel approaches for the treatment of infections by redirecting host immune responses against the pathogen. Such treatments may be most effectively applied at the mucosal locations which are frequently the sites of initial infection and may also suggest new approaches for vaccine development.

A novel D-amino acid oxidase from a contaminated agricultural soil metagenome and its characterization

A novel D-amino acid oxidase (DAAO) gene designated as daoE was cloned by the sequence-based screening of a plasmid metagenomic library of uncultured microorganisms from contaminated agricultural soil. The deduced amino acid sequence comparison and phylogenetic analysis indicated that daoE and other putative DAAOs are closely related. The putative DAAO gene was subcloned into a pETBlue-2 vector and overexpressed in Escherichia coli Tunner(DE3)pLacI. The recombinant protein was purified to homogeneity. The maximum activity of DaoE protein occurred at pH 8.0 and 37 °C. DaoE recombinant protein had an apparent K m of 2.96 mM, V max of 0.018 mM/min, k cat of 10.9/min, and k cat/K m of 1.16 × 10(4)/mol/min. The identification of this novel DAAO gene demonstrated the importance of metagenomic libraries in exploring new D-amino acid oxidases from environmental microorganisms to optimize their applications.

Combinatorial Libraries As a Tool for the Discovery of Novel, Broad-Spectrum Antibacterial Agents Targeting the ESKAPE Pathogens

Mixture based synthetic combinatorial libraries offer a tremendous enhancement for the rate of drug discovery, allowing the activity of millions of compounds to be assessed through the testing of exponentially fewer samples. In this study, we used a scaffold-ranking library to screen 37 different libraries for antibacterial activity against the ESKAPE pathogens. Each library contained between 10000 and 750000 structural analogues for a total of >6 million compounds. From this, we identified a bis-cyclic guanidine library that displayed strong antibacterial activity. A positional scanning library for these compounds was developed and used to identify the most effective functional groups at each variant position. Individual compounds were synthesized that were broadly active against all ESKAPE organisms at concentrations <2 μM. In addition, these compounds were bactericidal, had antibiofilm effects, showed limited potential for the development of resistance, and displayed almost no toxicity when tested against human lung cells and erythrocytes. Using a murine model of peritonitis, we also demonstrate that these agents are highly efficacious in vivo.

Antibiotic discovery: combatting bacterial resistance in cells and in biofilm communities

Bacterial resistance is a rapidly escalating threat to public health as our arsenal of effective antibiotics dwindles. Therefore, there is an urgent need for new antibiotics. Drug discovery has historically focused on bacteria growing in planktonic cultures. Many antibiotics were originally developed to target individual bacterial cells, being assessed in vitro against microorganisms in a planktonic mode of life. However, towards the end of the 20th century it became clear that many bacteria live as complex communities called biofilms in their natural habitat, and this includes habitats within a human host. The biofilm mode of life provides advantages to microorganisms, such as enhanced resistance towards environmental stresses, including antibiotic challenge. The community level resistance provided by biofilms is distinct from resistance mechanisms that operate at a cellular level, and cannot be overlooked in the development of novel strategies to combat infectious diseases. The review compares mechanisms of antibiotic resistance at cellular and community levels in the light of past and present antibiotic discovery efforts. Future perspectives on novel strategies for treatment of biofilm-related infectious diseases are explored.