Efficacy of Cathelicidin-Mimetic Antimicrobial Peptoids against Staphylococcus aureus.

Staphylococcus aureus is one of the most common pathogens associated with infection in wounds. The current standard of care uses a combination of disinfection and drainage followed by conventional antibiotics such as methicillin. Methicillin and vancomycin resistance has rendered these treatments ineffective, often causing the reemergence of infection. This study examines the use of antimicrobial peptoids (sequence-specific poly-N-substituted glycines) designed to mimic naturally occurring cationic, amphipathic host defense peptides, as an alternative to conventional antibiotics. These peptoids also show efficient and fast (<30 min) killing of methicillin-susceptible S. aureus (MSSA) and methicillin-resistant S. aureus (MRSA) at low micromolar concentrations without having apparent cytotoxic side effects in vivo. Additionally, these novel peptoids show excellent efficacy against biofilm formation and detachment for both MSSA and MRSA. In comparison, conventional antibiotics were unable to detach or prevent formation of biofilms. One cationic 12mer, Peptoid 1, shows great promise, as it could prevent formation of and detach biofilms at concentrations as low as 1.6 µM. The use of a bioluminescent S. aureus murine incision wound model demonstrated clearance of infection in peptoid-treated mice within 8 days, conveying another advantage these peptoids have over conventional antibiotics. These results provide clear evidence of the potential for antimicrobial peptoids for the treatment of S. aureus wound infections. IMPORTANCE Staphylococcus aureus resistance is a consistent problem with a large impact on the health care system. Infections with resistant S. aureus can cause serious adverse effects and can result in death. These antimicrobial peptoids show efficient killing of bacteria both as a biofilm and as free bacteria, often doing so in less than 30 min. As such, these antimicrobials have the potential to alleviate the burden that Staphylococcus infections have on the health care system and cause better outcomes for infected patients.

Phage-encoded cationic antimicrobial peptide required for lysis.

Most phages of Gram-negative hosts encode spanins for disruption of the outer membrane, the last step in host lysis. However, bioinformatic analysis indicates that ∼15% of these phages lack a spanin gene, suggesting they have an alternate way of disrupting the OM. Here, we show that the T7-like coliphage phiKT causes the explosive cell lysis associated with spanin activity despite not encoding spanins. A putative lysis cassette cloned from the phiKT late gene region includes the hypothetical novel gene 28 located between the holin and endolysin genes and supports inducible lysis in E. coli K-12. Moreover, induction of an isogenic construct lacking gene 28 resulted in divalent cation-stabilized spherical cells rather than lysis, implicating gp28 in OM disruption. Additionally, gp28 was shown to complement the lysis defect of a spanin-null λ lysogen. Gene 28 encodes a 56-amino acid cationic protein with predicted amphipathic helical structure and is membrane-associated after lysis. Urea and KCl washes did not release gp28 from the particulate, suggesting a strong hydrophobic membrane interaction. Fluorescence microscopy supports membrane localization of the gp28 protein prior to lysis. Gp28 is similar in size, charge, predicted fold, and membrane association to the human cathelicidin antimicrobial peptide LL-37. Synthesized gp28 behaved similar to LL-37 in standard assays mixing peptide and cells to measure bactericidal and inhibitory effects. Taken together, these results indicate that phiKT gp28 is a phage-encoded cationic antimicrobial peptide that disrupts bacterial outer membranes during host lysis and thus establishes a new class of phage lysis proteins, the disruptins. Significance We provide evidence that phiKT produces an antimicrobial peptide for outer membrane disruption during lysis. This protein, designated as a disruptin, is a new paradigm for phage lysis and has no similarities to other known lysis genes. Although many mechanisms have been proposed for the function of antimicrobial peptides, there is no consensus on the molecular basis of membrane disruption. Additionally, there is no established genetic system to support such studies. Therefore, the phiKT disruptin may represent the first genetically tractable antimicrobial peptide, facilitating mechanistic analyses.

Zinc limitation triggers anticipatory adaptations in Mycobacterium tuberculosis.

Mycobacterium tuberculosis (Mtb) has complex and dynamic interactions with the human host, and subpopulations of Mtb that emerge during infection can influence disease outcomes. This study implicates zinc ion (Zn2+) availability as a likely driver of bacterial phenotypic heterogeneity in vivo. Zn2+ sequestration is part of "nutritional immunity", where the immune system limits micronutrients to control pathogen growth, but this defense mechanism seems to be ineffective in controlling Mtb infection. Nonetheless, Zn2+-limitation is an environmental cue sensed by Mtb, as calprotectin triggers the zinc uptake regulator (Zur) regulon response in vitro and co-localizes with Zn2+-limited Mtb in vivo. Prolonged Zn2+ limitation leads to numerous physiological changes in vitro, including differential expression of certain antigens, alterations in lipid metabolism and distinct cell surface morphology. Furthermore, Mtb enduring limited Zn2+ employ defensive measures to fight oxidative stress, by increasing expression of proteins involved in DNA repair and antioxidant activity, including well described virulence factors KatG and AhpC, along with altered utilization of redox cofactors. Here, we propose a model in which prolonged Zn2+ limitation defines a population of Mtb with anticipatory adaptations against impending immune attack, based on the evidence that Zn2+-limited Mtb are more resistant to oxidative stress and exhibit increased survival and induce more severe pulmonary granulomas in mice. Considering that extracellular Mtb may transit through the Zn2+-limited caseum before infecting naïve immune cells or upon host-to-host transmission, the resulting phenotypic heterogeneity driven by varied Zn2+ availability likely plays a key role during early interactions with host cells.

Rapid Tuberculosis Diagnosis Using Reporter Enzyme Fluorescence.

Tuberculosis is the most frequent cause of death in humans from a single infectious agent. Due to low numbers of bacteria present in sputum during early infection, diagnosis does not usually occur until >3 to 4 months after symptoms develop. We created a new more sensitive diagnostic that can be carried out in 10 min with no processing or technical expertise. This assay utilizes the Mycobacterium tuberculosis-specific biomarker BlaC in reporter enzyme fluorescence (REF) that has been optimized for clinical samples, designated REFtb, along with a more specific fluorogenic substrate, CDG-3. We report the first evaluation of clinical specimens with REFtb assays in comparison to the gold standards for tuberculosis diagnosis, culture and smear microscopy. REFtb assays allowed diagnosis of 160 patients from 16 different countries with a sensitivity of 89% for smear-positive, culture-positive samples and 88% for smear-negative, culture-positive samples with a specificity of 82%. The negative predictive value of REFtb for tuberculosis infection is 93%, and the positive predictive value is 79%. Overall, these data point toward the need for larger accuracy studies by third parties using a commercially available REFtb kit to determine whether incorporation of REFtb into the clinical toolbox for suspected tuberculosis patients would improve case identification. If results similar to our own can be obtained by all diagnostic laboratories, REFtb would allow proper treatment of more than 85% of patients that would be missed during their initial visit to a clinic using current diagnostic strategies, reducing the potential for further spread of disease.

Legionnaires' Disease Mortality in Guinea Pigs Involves the p45 Mobile Genomic Element.

BACKGROUND: Legionella can cause Legionnaires' disease, a potentially fatal form of pneumonia that occurs as sporadic epidemics. Not all strains display the same propensity to cause disease in humans. Because Legionella pneumophila serogroup 1 is responsible for >85% of infections, the majority of studies have examined this serogroup, but there are 3 commonly used laboratory strains: L pneumophila serogroup 1 Philadelphia (Phil-1)-derived strains JR32 and Lp01 and 130b-derived strain AA100. METHODS: We evaluated the ability of Phil-1, JR32, Lp01, and AA100 to cause disease in guinea pigs. RESULTS: We found that, although Phil-1, JR32, and AA100 cause an acute pneumonia and death by 4 days postinfection (100%), strain Lp01 does not cause mortality (0%). We also noted that Lp01 lacks a mobile element, designated p45, whose presence correlates with virulence. Transfer of p45 into Lp01 results in recovery of the ability of this strain to cause mortality, leads to more pronounced disease, and correlates with increased interferon-γ levels in the lungs and spleens before death. CONCLUSIONS: These observations suggest a mechanism of Legionnaires' disease pathogenesis due to the presence of type IVA secretion systems that cause higher mortality due to overinduction of a proinflammatory response in the host.

Legionella pneumophila p45 element influences host cell entry and sensitivity to sodium.

Legionella pneumophila are environmental bacteria found ubiquitously in both natural and man-made water reservoirs, sometimes as constituents of biofilm communities, but mostly intracellularly within protozoal hosts. In the event that Legionella become aerosolized in water droplets and inhaled by humans, they can cause a potentially fatal form of pneumonia called Legionnaires' disease. Strains of L. pneumophila have highly plastic genomes that harbor numerous inter- and intra-genomic elements, enhancing their ability to live under diverse environmental conditions. One such mobile genomic element, p45 carries ~45 kbp of genes, including the Lvh (Legionella Vir homolog) type IVa secretion system. This element was evaluated for its contribution to L. pneumophila environmental resilience and virulence-related characteristics by comparing clinically isolated strain Philadelphia-1 that carries p45, Lp01 that lacks p45, and Lp01 with p45 reintroduced, Lp01+p45. We found that the p45 element impacts host cell entry and resistance to sodium, both virulence-related characteristics in Legionella species.

Hetero-Multivalency of Pseudomonas aeruginosa Lectin LecA Binding to Model Membranes.

A single glycan-lectin interaction is often weak and semi-specific. Multiple binding domains in a single lectin can bind with multiple glycan molecules simultaneously, making it difficult for the classic "lock-and-key" model to explain these interactions. We demonstrated that hetero-multivalency, a homo-oligomeric protein simultaneously binding to at least two types of ligands, influences LecA (a Pseudomonas aeruginosa adhesin)-glycolipid recognition. We also observed enhanced binding between P. aeruginosa and mixed glycolipid liposomes. Interestingly, strong ligands could activate weaker binding ligands leading to higher LecA binding capacity. This hetero-multivalency is probably mediated via a simple mechanism, Reduction of Dimensionality (RD). To understand the influence of RD, we also modeled LecA's two-step binding process with membranes using a kinetic Monte Carlo simulation. The simulation identified the frequency of low-affinity ligand encounters with bound LecA and the bound LecA's retention of the low-affinity ligand as essential parameters for triggering hetero-multivalent binding, agreeing with experimental observations. The hetero-multivalency can alter lectin binding properties, including avidities, capacities, and kinetics, and therefore, it likely occurs in various multivalent binding systems. Using hetero-multivalency concept, we also offered a new strategy to design high-affinity drug carriers for targeted drug delivery.

Imaging Mycobacterium tuberculosis in Mice with Reporter Enzyme Fluorescence.

Reporter enzyme fluorescence (REF) utilizes substrates that are specific for enzymes present in target organisms of interest for imaging or detection by fluorescence or bioluminescence. We utilize BlaC, an enzyme expressed constitutively by all M. tuberculosis strains. REF allows rapid quantification of bacteria in lungs of infected mice. The same group of mice can be imaged at many time points, greatly reducing costs, enumerating bacteria more quickly, allowing novel observations in host-pathogen interactions, and increasing statistical power, since more animals per group are readily maintained. REF is extremely sensitive due to the catalytic nature of the BlaC enzymatic reporter and specific due to the custom flourescence resonance energy transfer (FRET) or fluorogenic substrates used. REF does not require recombinant strains, ensuring normal host-pathogen interactions. We describe the imaging of M. tuberculosis infection using a FRET substrate with maximal emission at 800 nm. The wavelength of the substrate allows sensitive deep tissue imaging in mammals. We will outline aerosol infection of mice with M. tuberculosis, anesthesia of mice, administration of the REF substrate, and optical imaging. This method has been successfully applied to evaluating host-pathogen interactions and efficacy of antibiotics targeting M. tuberculosis.

Guinea pig infection with the intracellular pathogen Rhodococcus equi.

Rhodococcus equi is an opportunistic, intracellular pathogen that causes pyogranulomatous pneumonia in foals and immunocompromised people. Currently, there is no experimental model of R. equi pneumonia other than intra-bronchial experimental infection of foals with R. equi, which is labor-intensive and costly. This study's objective was to develop a guinea pig (GP) model of R. equi pneumonia that would facilitate development of novel approaches for controlling and preventing this disease. Guinea pigs were infected with either 101, 102, 103, or 104 colony forming units (CFUs) of a virulent strain of R. equi using a Madison aerosol chamber, or 106 or 107 CFUs of this strain intratracheally. Animals were monitored daily for clinical signs of pneumonia, and were euthanized and necropsied on days 1, 3, 7, or 35 post-infection (PI). Lung homogenates were plated onto selective agar to determine bacterial load. No clinical signs of disease were observed regardless of the inoculum dose or infection method. No bacteria were recovered from GPs euthanized at 35 days PI. Histology and immunostaining of T-cells, B-cells, and macrophages in lungs showed that inflammatory responses in infected GPs were similarly unremarkable irrespective of dose or route of infection. Guinea pigs appear to be resistant to pulmonary infection with virulent R. equi even at doses that reliably produce clinical pneumonia in foals.

Thioaptamer targeted discoidal microparticles increase self immunity and reduce Mycobacterium tuberculosis burden in mice.

Worldwide, tuberculosis (TB) remains one of the most prevalent infectious diseases causing morbidity and death in >1.5 million patients annually. Mycobacterium tuberculosis (Mtb), the etiologic agent of TB, usually resides in the alveolar macrophages. Current tuberculosis treatment methods require more than six months, and low compliance often leads to therapeutic failure and multidrug resistant strain development. Critical to improving TB-therapy is shortening treatment duration and increasing therapeutic efficacy. In this study, we sought to determine if lung hemodynamics and pathological changes in Mtb infected cells can be used for the selective targeting of microparticles to infected tissue(s). Thioaptamers (TA) with CD44 (CD44TA) targeting moiety were conjugated to discoidal silicon mesoporous microparticles (SMP) to enhance accumulation of these agents/carriers in the infected macrophages in the lungs. In vitro, CD44TA-SMP accumulated in macrophages infected with mycobacteria efficiently killing the infected cells and decreasing survival of mycobacteria. In vivo, increased accumulations of CD44TA-SMP were recorded in the lung of M. tuberculosis infected mice as compared to controls. TA-targeted carriers significantly diminished bacterial load in the lungs and caused recruitment of T lymphocytes. Proposed mechanism of action of the designed vector accounts for a combination of increased uptake of particles that leads to infected macrophage death, as well as, activation of cellular immunity by the TA, causing increased T-cell accumulation in the treated lungs. Based on our data with CD44TA-SMP, we anticipate that this drug carrier can open new avenues in TB management.

Polyelectrolyte Multilayer Nanocoating Dramatically Reduces Bacterial Adhesion to Polyester Fabric.

Bacterial adhesion to textiles is thought to contribute to odor and infection. Alternately exposing polyester fabric to aqueous solutions of poly(diallyldimethylammonium chloride) (PDDA) and poly(acrylic acid) (PAA) is shown here to create a nanocoating that dramatically reduces bacterial adhesion. Ten PDDA/PAA bilayers (BL) are 180 nm thick and only increase the weight of the polyester by 2.5%. The increased surface roughness and high degree of PAA ionization leads to a surface with a negative charge that causes a reduction in adhesion of Staphylococcus aureus by 50% when compared to uncoated fabric, after rinsing with sterilized water, because of electrostatic repulsion. S. aureus bacterial adhesion was quantified using bioluminescent radiance measured before and after rinsing, revealing 99% of applied bacteria were removed with a ten bilayer PDDA/PAA nanocoating. The ease of processing, and benign nature of the polymers used, should make this technology useful for rendering textiles antifouling on an industrial scale.

New directions using reporter enzyme fluorescence (REF) as a tuberculosis diagnostic platform.

Although tuberculosis (TB) is one of the most common causes of morbidity and mortality in humans worldwide and diagnostic methods have been in place for more than 100 years, diagnosis remains a challenge. The main problems with diagnosis relate to the time needed to obtain a definitive result, difficulty in obtaining sputum, the primary clinical material used, and the ability of the causative agent, Mycobacterium tuberculosis, to cause disease in nearly any tissue within the body. In order to decrease incidence of TB, discovery of a novel interventions will be required, since current technologies have only been able to control numbers of infections, not reduce them. Diagnostic innovation is particularly needed because there are no effective pediatric or extrapulmonary TB diagnostic methods and multiple-drug resistance is only identified in less than 25% of those patients that are thought to have it. The most common diagnostic method worldwide remains acid-fast stain on sputum, with a threshold of ∼10,000 bacteria/ml that is only reached ∼5-6 months after development of symptoms. In order to obtain definitive diagnostic results earlier during the disease process, we have developed a diagnostic method designated reporter enzyme fluorescence (REF) that utilizes BlaC produced by M. tuberculosis and custom substrates to produce a specific fluorescent signal with as few as 10 bacteria/ml in clinical samples. We believe that the unique biology of the REF technique will allow it to contribute new diagnostic information that is complementary to all existing diagnostic tests as well as those currently known to be in development.

Fluorogenic probes with substitutions at the 2 and 7 positions of cephalosporin are highly BlaC-specific for rapid Mycobacterium tuberculosis detection.

Current methods for the detection of Mycobacterium tuberculosis (Mtb) are either time consuming or require expensive instruments and are thus are not suitable for point-of-care diagnosis. The design, synthesis, and evaluation of fluorogenic probes with high specificity for BlaC, a biomarker expressed by Mtb, are described. The fluorogenic probe CDG-3 is based on cephalosporin with substitutions at the 2 and 7 positions and it demonstrates over 120,000-fold selectivity for BlaC over TEM-1 Bla, the most common ß-lactamase. CDG-3 can detect 10 colony-forming units of the attenuated Mycobacterium bovis strain BCG in human sputum in the presence of high levels of contaminating ß-lactamases expressed by other clinically prevalent bacterial strains. In a trial with 50 clinical samples, CDG-3 detected tuberculosis with 90% sensitivity and 73% specificity relative to Mtb culture within one hour, thus demonstrating its potential as a low-cost point-of-care test for use in resource-limited areas.

A novel inducer of Roseobacter motility is also a disruptor of algal symbiosis.

Silicibacter sp. strain TM1040, a member of the Roseobacter clade, forms a symbiosis with unicellular phytoplankton, which is inextricably linked to the biphasic "swim or stick" lifestyle of the bacteria. Mutations in flaC bias the population toward the motile phase. Renewed examination of the FlaC(-) strain (HG1016) uncovered that it is composed of two different cells: a pigmented type, PS01, and a nonpigmented cell, PS02, each of which has an identical mutation in flaC. While monocultures of PS01 and PS02 had few motile cells (0.6 and 6%, respectively), coculturing the two strains resulted in a 10-fold increase in the number of motile cells. Cell-free supernatants from coculture or wild-type cells were fully capable of restoring motility to PS01 and PS02, which was due to increased fliC3 (flagellin) transcription, FliC3 protein levels per cell, and flagella synthesis. The motility-inducing compound has an estimated mass of 226 Da, as determined by mass spectrometry, and is referred to as Roseobacter Motility Inducer (RMI). Mutations affecting genes involved in phenyl acetic acid synthesis significantly reduced RMI, while defects in tropodithietic acid (TDA) synthesis had marginal or no effect on RMI. RMI biosynthesis is induced by p-coumaric acid, a product of algal lignin degradation. When added to algal cultures, RMI caused loss of motility, cell enlargement, and vacuolization in the algal cells. RMI is a new member of the roseobacticide family of troponoid compounds whose activities affect roseobacters, by shifting their population toward motility, as well as their phytoplankton hosts, through an algicidal effect.

Regulation of cell division, biofilm formation, and virulence by FlhC in Escherichia coli O157:H7 grown on meat.

To understand the continuous problems that Escherichia coli O157:H7 causes as food pathogen, this study assessed global gene regulation in bacteria growing on meat. Since FlhD/FlhC of E. coli K-12 laboratory strains was previously established as a major control point in transducing signals from the environment to several cellular processes, this study compared the expression pattern of an E. coli O157:H7 parent strain to that of its isogenic flhC mutant. This was done with bacteria that had been grown on meat. Microarray experiments revealed 287 putative targets of FlhC. Real-time PCR was performed as an alternative estimate of transcription and confirmed microarray data for 13 out of 15 genes tested (87%). The confirmed genes are representative of cellular functions, such as central metabolism, cell division, biofilm formation, and pathogenicity. An additional 13 genes from the same cellular functions that had not been hypothesized as being regulated by FlhC by the microarray experiment were tested with real-time PCR and also exhibited higher expression levels in the flhC mutant than in the parent strain. Physiological experiments were performed and confirmed that FlhC reduced the cell division rate, the amount of biofilm biomass, and pathogenicity in a chicken embryo lethality model. Altogether, this study provides valuable insight into the complex regulatory network of the pathogen that enables its survival under various environmental conditions. This information may be used to develop strategies that could be used to reduce the number of cells or pathogenicity of E. coli O157:H7 on meat by interfering with the signal transduction pathways.

Environmental and genetic factors that contribute to Escherichia coli K-12 biofilm formation.

Biofilms are communities of bacteria whose formation on surfaces requires a large portion of the bacteria's transcriptional network. To identify environmental conditions and transcriptional regulators that contribute to sensing these conditions, we used a high-throughput approach to monitor biofilm biomass produced by an isogenic set of Escherichia coli K-12 strains grown under combinations of environmental conditions. Of the environmental combinations, growth in tryptic soy broth at 37 degrees C supported the most biofilm production. To analyze the complex relationships between the diverse cell-surface organelles, transcriptional regulators, and metabolic enzymes represented by the tested mutant set, we used a novel vector-item pattern-mining algorithm. The algorithm related biofilm amounts to the functional annotations of each mutated protein. The pattern with the best statistical significance was the gene ontology 'pyruvate catabolic process,' which is associated with enzymes of acetate metabolism. Phenotype microarray experiments illustrated that carbon sources that are metabolized to acetyl-coenzyme A, acetyl phosphate, and acetate are particularly supportive of biofilm formation. Scanning electron microscopy revealed structural differences between mutants that lack acetate metabolism enzymes and their parent and confirmed the quantitative differences. We conclude that acetate metabolism functions as a metabolic sensor, transmitting changes in environmental conditions to biofilm biomass and structure.

Relating gene expression data on two-component systems to functional annotations in Escherichia coli.

BACKGROUND: Obtaining physiological insights from microarray experiments requires computational techniques that relate gene expression data to functional information. Traditionally, this has been done in two consecutive steps. The first step identifies important genes through clustering or statistical techniques, while the second step assigns biological functions to the identified groups. Recently, techniques have been developed that identify such relationships in a single step. RESULTS: We have developed an algorithm that relates patterns of gene expression in a set of microarray experiments to functional groups in one step. Our only assumption is that patterns co-occur frequently. The effectiveness of the algorithm is demonstrated as part of a study of regulation by two-component systems in Escherichia coli. The significance of the relationships between expression data and functional annotations is evaluated based on density histograms that are constructed using product similarity among expression vectors. We present a biological analysis of three of the resulting functional groups of proteins, develop hypotheses for further biological studies, and test one of these hypotheses experimentally. A comparison with other algorithms and a different data set is presented. CONCLUSION: Our new algorithm is able to find interesting and biologically meaningful relationships, not found by other algorithms, in previously analyzed data sets. Scaling of the algorithm to large data sets can be achieved based on a theoretical model.