Evaluation of bacterial survival and phagocyte function with a fluorescence-based microplate assay

Antimicrobial Peptide-Poly(ethylene glycol) Conjugates: Connecting Molecular Architecture, Solution Properties, and Functional Performance

Antimicrobial peptides (AMPs) are promising alternatives to conventional antibiotics for treating infections caused by drug-resistant bacteria; yet, many peptides are limited by toxicity to eukaryotic cells and instability in biological environments. Conjugation to linear polymers that reduce cytotoxicity and improve stability, however, often decreases antimicrobial activity. In this work, we combine the biocompatibility advantages of poly(ethylene glycol) (PEG) with the efficacy merits of nonlinear polymer architectures that accommodate multiple AMPs per molecule. By conjugating a chemokine-derived AMP, stapled Ac-P9, to linear and star-shaped PEG with various arm numbers and lengths, we investigated the role of molecular architecture in solution properties (i.e., ζ-potential, size, and morphology) and performance (i.e., antimicrobial activity, hemolysis, and protease resistance). Linear, 4-arm, and 8-arm conjugates with 2-2.5 kDa PEG arms were found to form nanoscale structures in solution with lower ζ-potentials relative to the unconjugated AMP, suggesting that the polymer partially shields the cationic AMP. Reducing the length of the PEG arms of the 8-arm conjugate to 1.25 kDa appeared to better reveal the peptide, seen by the increased ζ-potential, and promote assembly into particles with a larger size and defined spherical morphology. The antimicrobial effects exerted by the short 8-arm conjugate rivaled that of the unconjugated peptide, and the AMP constituents of the short 8-arm conjugate were protected from proteolytic degradation. All other conjugates examined also imparted a degree of protease resistance, but exhibited some reduced level of antimicrobial activity as compared to the AMP alone. None of the conjugates caused significant cytotoxic effects, which bodes well for their future potential to treat infections. While enhancing proteolytic stability often comes with the cost of lower antimicrobial activity, we have found that presenting AMPs at high density on a neutral nonlinear polymer strikes a favorable balance, exhibiting both enhanced stability and high antimicrobial activity.

Disparate Regions of the Human Chemokine CXCL10 Exhibit Broad-Spectrum Antimicrobial Activity against Biodefense and Antibiotic-Resistant Bacterial Pathogens

CXCL10 is a pro-inflammatory chemokine produced by the host in response to microbial infection. In addition to canonical, receptor-dependent actions affecting immune-cell migration and activation, CXCL10 has also been found to directly kill a broad range of pathogenic bacteria. Prior investigations suggest that the bactericidal effects of CXCL10 occur through two distinct pathways that compromise the cell envelope. These observations raise the intriguing notion that CXCL10 features a separable pair of antimicrobial domains. Herein, we affirm this possibility through peptide-based mapping and structure/function analyses, which demonstrate that discrete peptides derived from the N- and C-terminal regions of CXCL10 mediate bacterial killing. The N-terminal derivative, peptide P1, exhibited marked antimicrobial activity against Bacillus anthracis vegetative bacilli and spores, as well as antibiotic-resistant clinical isolates of Klebsiella pneumoniae, Acinetobacter baumannii, Enterococcus faecium, and Staphylococcus aureus, among others. At bactericidal concentrations, peptide P1 had a minimal degree of chemotactic activity, but did not cause red blood cell hemolysis or cytotoxic effects against primary human cells. The C-terminal derivative, peptide P9, exhibited antimicrobial effects, but only against Gram-negative bacteria in low-salt medium─conditions under which the peptide can adopt an α-helical conformation. The introduction of a hydrocarbon staple induced and stabilized α-helicity; accordingly, stapled peptide P9 displayed significantly improved bactericidal effects against both Gram-positive and Gram-negative bacteria in media containing physiologic levels of salt. Together, our findings identify and characterize the antimicrobial regions of CXCL10 and functionalize these novel determinants as discrete peptides with potential therapeutic utility against difficult-to-treat pathogens.

Microfluidics Microbial Activity MicroAssay: An Automated In Situ Microbial Metabolic Detection System

With no direct extant-life detection instrumentation included in a space mission since the 1970s, the advancement of new technologies to be included in future space missions is imperative. We developed, optimized, and tested a semi-automated prototype, the microfluidics Microbial Activity MicroAssay (μMAMA). This system metabolically characterizes and detects extant microbial life by way of metabolism-indicator redox dyes. We first evaluated the robustness and sensitivity of six redox dye/buffer combinations, and we then tested their responses to metabolic activity in astrobiological analog high-Arctic samples. We determined that the Biolog Inoculating Fluid (IF)-C and AlamarBlue buffered in IF-0a (aB-IF0a) dye/buffer combinations were optimal, as they detected metabolic activity from the fewest microbial cells (10² cells/mL) while maintaining efficacy over a broad physiochemical range of pH (0-13), temperature (-10°C to 37°C), salinity and perchlorate (tested up to 30%), and in the presence of a Mars regolith simulant (MMS-2). The μMAMA, which incorporated these redox dyes, detected extant active cold-adapted microbial life from high Arctic analog sites, including samples amended with substrates targeting chemolithoautotrophic metabolisms. Given μMAMA's small size (we estimate a complete planetary instrument could occupy as little as 3 L) and potential for automation, it could easily be incorporated into almost any landed platform for life detection missions.

A new analysis method for evaluating bacterial growth with microplate readers

Growth curve measurements are commonly used in microbiology, while the use of microplate readers for such measurements provides better temporal resolution and higher throughput. However, evaluating bacterial growth with microplate readers has been hurdled by barriers such as multiple scattering. Here, we report our development of a method based on the time derivatives of the optical density (OD) and/or fluorescence (FL) of bacterial cultures to overcome these barriers. First, we illustrated our method using quantitative models and numerical simulations, which predicted the number of bacteria and the number of fluorescent proteins in time as well as their time derivatives. Then, we systematically investigated how the time derivatives depend on the parameters in the models/simulations, providing a framework for understanding the FL growth curves. In addition, as a demonstration, we applied our method to study the lag time elongation of bacteria subjected to treatment with silver (Ag⁺) ions and found that the results from our method corroborated well with that from growth curve fitting by the Gompertz model that has been commonly used in the literature. Furthermore, this method was applied to the growth of bacteria in the presence of silver nanoparticles (AgNPs) at various concentrations, where the OD curve measurements failed. We showed that our method allowed us to successfully extract the growth behavior of the bacteria from the FL measurements and understand how the growth was affected by the AgNPs.

Salmonella enterica serovar Typhimurium inhibits the innate immune response and promotes apoptosis in a ribosomal/TRP53-dependent manner in swine neutrophils

Neutrophils are the first barriers for resisting the invasion, proliferation, and damage caused by Salmonella Typhimurium. However, the mechanisms that control this resistance are not completely understood. In this study, we established an in vitro Salmonella infection model in porcine neutrophils, and analyzed the cellular transcriptome by deep sequencing and flow cytometry. The results showed that ribosomal gene transcription was inhibited, and two of these genes, RPL39 and RPL9, were related to TRP53 activation. Furthermore, several important innate immunity genes were also inhibited. Knock-down of RPL39 and RPL9 by siRNA caused an approximate fourfold up-regulation of TRP53. Knock-down of RPL39 and RPL9 also resulted in a significant down-regulation of IFNG and TNF, indicating an inhibition of the innate immune response. Silencing of RPL39 and RPL9 also resulted in the up-regulation of FAS, RB1, CASP6, and GADD45A, which play roles in cell cycle arrest and apoptosis. Neutrophils were either first treated with RPL39 siRNA, RPL9 siRNA, TRP53 activator, or TRP53 inhibitor, and then infected with Salmonella. Knock-down of RPL39 and RPL9, or treatment with TRP53 activator, can increase the intracellular proliferation of Salmonella in neutrophils. We speculate that much of the Salmonella virulence can be attributed to the enhancement of cell cycle arrest and the inhibition of the innate immune response, which allows the bacteria to successfully proliferate intracellularly.

The Antimicrobial Peptide Human Beta-Defensin 2 Inhibits Biofilm Production of Pseudomonas aeruginosa Without Compromising Metabolic Activity

Biofilm production is a key virulence factor that facilitates bacterial colonization on host surfaces and is regulated by complex pathways, including quorum sensing, that also control pigment production, among others. To limit colonization, epithelial cells, as part of the first line of defense, utilize a variety of antimicrobial peptides (AMPs) including defensins. Pore formation is the best investigated mechanism for the bactericidal activity of AMPs. Considering the induction of human beta-defensin 2 (HBD2) secretion to the epithelial surface in response to bacteria and the importance of biofilm in microbial infection, we hypothesized that HBD2 has biofilm inhibitory activity. We assessed the viability and biofilm formation of a pyorubin-producing Pseudomonas aeruginosa strain in the presence and absence of HBD2 in comparison to the highly bactericidal HBD3. At nanomolar concentrations, HBD2 - independent of its chiral state - significantly reduced biofilm formation but not metabolic activity, unlike HBD3, which reduced biofilm and metabolic activity to the same degree. A similar discrepancy between biofilm inhibition and maintenance of metabolic activity was also observed in HBD2 treated Acinetobacter baumannii, another Gram-negative bacterium. There was no evidence for HBD2 interference with the regulation of biofilm production. The expression of biofilm-related genes and the extracellular accumulation of pyorubin pigment, another quorum sensing controlled product, did not differ significantly between HBD2 treated and control bacteria, and in silico modeling did not support direct binding of HBD2 to quorum sensing molecules. However, alterations in the outer membrane protein profile accompanied by surface topology changes, documented by atomic force microscopy, was observed after HBD2 treatment. This suggests that HBD2 induces structural changes that interfere with the transport of biofilm precursors into the extracellular space. Taken together, these data support a novel mechanism of biofilm inhibition by nanomolar concentrations of HBD2 that is independent of biofilm regulatory pathways.

Rapid determination of carbapenem resistance by low-cost colorimetric methods: Propidium Iodide and alamar blue staining

Carbapenems are a class of β-lactam antibiotics with a broad antimicrobial activity spectrum. Owing to their sturdy structures resistant to most β-lactamases, they have been regarded as one of the last-resort antibiotics for combating multidrugresistant bacterial infections. However, the emergence of carbapenem resistance increases predominantly in nosocomial pathogens. To prevent spread of carbapenem resistance in early stages, it is imperative to develop rapid diagnostic tests that will substantially reduce the time and cost in determining carbapenem resistance. Thus, we devised a staining-based diagnostic method applicable to three different Gram-negative pathogens of Acinetobacter baumannii, Escherichia coli, and Klebsiella pneumoniae, all with the high potential to develop carbapenem resistance. Regardless of the resistance mechanisms presented by bacterial species and strains, double staining with propidium iodide (PI) and alamar blue (AB) identified resistant bacteria with an average sensitivity of 95.35%, 7 h after imipenem treatments in 343 clinical isolates. Among the three species tested, A. baumannii showed the highest diagnostic sensitivity of 98.46%. The PI and ABmediated staining method could be a promising diagnostic method with high-throughput efficacy and low cost.

Optimization of a real-time high-throughput assay for assessment of Streptococcus mutans metabolism and screening of antibacterial dental adhesives

Objective.

The present work shows the optimization of a high-throughput bioluminescence assay to assess the metabolism of intact Streptococcus mutans biofilms and its utility as a screening method for nanofilled antibacterial dental materials.

Methods.

The assay was optimized by monitoring changes in bioluminescence mediated by variation of the experimental parameters investigated (growth media and sucrose concentration, inoculum:D-Luciferin ratio, dilution factor, inoculum volume, luminescence wavelength, replicate and luciferase metabolic activity). Confocal microscopy was then used to demonstrate the impact of biofilm growth conditions on the 3-D distribution of extracellular polymeric substance (EPS) within Streptococcus mutans biofilms and its implications as confounding factors in high-throughput studies (HTS).

Results.

Relative Luminescence Unit (RLU) values from the HTS optimization were analyzed by multivariate ANOVA (α = 0.05) and coefficients of variation, whereas data from 3-D structural parameters and RLU values of biofilms grown on experimental antibacterial dental adhesive resins were analyzed using General Linear Models and Student–Newman–Keuls post hoc tests (α = 0.05). Confocal microscopy demonstrated that biofilm growth conditions significantly influenced the quantity and distribution of EPS within the 3-D structures of the biofilms. An optimized HTS bioluminescence assay was developed and its applicability as a screening method in dentistry was demonstrated using nanofilled experimental antibacterial dental adhesive resins.

Significance.

The present study is anticipated to positively impact the direction of future biofilm research in dentistry, because it offers fundamental information for the design of metabolic-based assays, increases the current levels of standardization and reproducibility while offering a tool to decrease intra-study variability.

Preferential dipeptide incorporation of Porphyromonas gingivalis mediated by proton-dependent oligopeptide transporter (Pot)

Multiple dipeptidyl-peptidases (DPPs) are present in the periplasmic space of Porphyromonas gingivalis, an asaccharolytic periodontopathic bacterium. Dipeptides produced by DPPs are presumed to be transported into the bacterial cells and metabolized to generate energy and cellular components. The present study aimed to identify a transporter responsible for dipeptide uptake in the bacterium. A real-time metabolic analysis demonstrated that P. gingivalis preferentially incorporated Gly-Xaa dipeptides, and then, single amino acids, tripeptides and longer oligopeptides to lesser extents. Heterologous expression of the P. gingivalis serine/threonine transporter (SstT; PGN_1460), oligopeptide transporter (Opt; PGN_1518) and proton-dependent oligopeptide transporter (Pot; PGN_0135) genes demonstrated that Escherichia coli expressing Pot exclusively incorporated Gly-Gly, while SstT managed Ser uptake and Opt was responsible for Gly-Gly-Gly uptake. Dipeptide uptake was significantly decreased in a P. gingivalis Δpot strain and further suppressed in a Δpot-Δopt double-deficient strain. In addition, the growth of the Δpot strain was markedly attenuated and the Δpot-Δopt strain scarcely grew, whereas the ΔsstT strain grew well almost like wild type. Consequently, these results demonstrate that predominant uptake of dipeptide in P. gingivalis is mostly managed by Pot. We thus propose that Pot is a potential therapeutic target of periodontal disease and P. gingivalis-related systemic diseases.

Resazurin assay for assessment of antimicrobial properties of electrospun nanofiber filtration membranes

We developed a simple and fast microplate assay for evaluation of the antimicrobial activity of electrospun nanofiber filtration membranes or similar porous materials for water treatment technologies. Resazurin (alamarBlue®) was used as an indicator of the amount of viable experimental microorganisms Gram-negative Escherichia coli, Gram-positive Enterococcus faecalis, and natural wastewater treatment plant effluent bacteria. A bacterial inoculum of concentration 1-3 × 105 CFU mL-1 was pipetted onto the surface of assessed both functionalized and respective control membranes and incubated in 12-well plates for 4 h at 37 °C. Kinetics of resazurin metabolization, i.e. its reduction to fluorescent resorufin, was evaluated fluorimetrically (λex520/λem590 nm). A number of viable bacteria on the membranes expressed as CFU mL-1 was calculated from the kinetic curves by using calibration curves that were constructed for both experimental bacterial species. Antimicrobial activities of the membranes were evaluated by either resazurin assay or modified ISO 20743 plate count assay. Results of both assays showed the significant antimicrobial activity of membranes functionalized with silver nanoparticles for both bacterial species and wastewater treatment plant effluent bacteria as well (log CFU reduction compared to control membrane > 4), while membranes containing specific quaternary ammonium salts were inefficient (log CFU reduction < 1). The suitability of resazurin microplate assay for testing nanofiber filtration membranes and analogous matrices has proven to be a faster and less demanding alternative to the traditionally used approach providing comparable results.

Cas13-induced cellular dormancy prevents the rise of CRISPR-resistant bacteriophage

Clustered, regularly interspaced, short palindromic repeat (CRISPR) loci of prokaryotes are composed of 30-40 bp repeats separated by equally short sequences of plasmid and bacteriophage origin known as spacers^1–3. Spacers are transcribed and processed into short CRISPR RNAs (crRNAs) that are used as guides by CRISPR-associated (Cas) nucleases to recognize and destroy complementary sequences (known as protospacers) within invaders^4,5. In contrast to most Cas nucleases which destroy the invader’s DNA^4–7, the type VI effector nuclease Cas13 employs RNA guides to locate complementary transcripts and catalyze both sequence-specific cis-, and non-specific trans-RNA cleavage⁸. While it has been hypothesized that Cas13 naturally defends against RNA phages⁸, type VI spacer sequences have exclusively been found to match the genomes of double-stranded DNA (dsDNA) phages^9,10, suggesting that Cas13 can provide immunity against these invaders. However, whether and how Cas13 utilizes the cis- and/or trans-RNA cleavage activities in defending against dsDNA phages is not understood. Here we show that trans-cleavage of transcripts halts the growth of the host cell and results in the abortion of the infectious cycle. This depletes the phage population and provides herd immunity to uninfected bacteria. Phages harboring target mutations, which easily evade DNA-targeting CRISPR systems^11–13, are also depleted due to the activation of Cas13 by co-infecting wild type phages. Thus, by acting on the host rather than directly targeting the virus, type VI CRISPR systems not only provide robust defense against DNA phages but also prevent outbreaks of CRISPR-resistant phage.

Molecular analysis and genotyping of pathogenicity locus in Clostridioides difficile strains isolated from patients in Tehran hospitals during the years 2007-2010

BACKGROUND & AIMS

Clostridioides difficile (C. difficile) has been identified as the leading cause of antibiotic associated diarrhea (AAD). Co-carriage of an intact pathogenicity locus (PaLoc) with binary toxin genes in C. difficile strains seems to be linked with severe disease outcomes in the infected patients. Epidemiology of C. difficile infection (CDI) in hospital setting and knowledge about their genetic context help us to decrease the morbidity, mortality, and costs associated with Clostridioides difficile infection. In the present study was aimed to characterize genetic diversity of PaLoc among different C. difficile strains isolated from hospitalized patients and carriage of cytolethal distending toxin gene (cdt) in different hospitals.

METHOD

C. difficile strains were isolated from stool samples of inpatients referred to a reference laboratory from different hospitals and also outpatients with diarrhea, during 2008-2011. DNA was extracted from pure culture of the bacterium and PCR was performed for tcdA, tcdB, tcdE, tcdC, tcdD, and cdu2 genes. Carriage of two binary toxin genes cdtA, cdtB was also determined in these strains. To find clonal strains, similarity of genotypes and integrity of PaLoc among the isolates was compared in each hospital.

RESULTS

The intact PaLoc was found most frequently among the isolates in the outpatients (19/51, 37.2%, Group I), while incomplete PaLoc found mostly in patients who were hospitalized in the infectious diseases and internal diagnosis wards. tcdA and tcdB genes were detected in different combinations among the studied strains. These strains showed tcdA⁺B⁺, tcdA⁺B^-, and tcdA^-B⁺ genotypes in a frequency of 76.4% (39/51), 7.8% (4/51), and 17.6% (9/51), respectively. Analysis of gene composition of the PaLoc showed 19 distinct genotypes among the 51 strains. Accordingly, 38 strains were classified mainly into 6 regular groups, while the remaining strains showed heterogeneous patterns. tcdC^-/tcdD^- constituted the most common genotypic group among the strains with partial PaLoc (7/51, 13.7%). A hypertoxigenic genotype, tcdC^-/tcdA⁺/tcdB⁺, was detected in 2 strains (2/51, 3.9%). The intact genotype was also detected in a C. difficile isolate from outpatients. Cdt encoding genes toxins was observed in low numbers of the strains (7/52, 13.5%). All of cdtA⁺B⁺ strains were belonged to PaLoc group 1 (intact genotype). Statistical analyses showed no correlation between particular genotypes and special wards of the hospitals (p value>0.05).

CONCLUSION

Collectively, our results showed diversity of C. difficile strains in most wards of the studied hospitals. Diversity of PaLoc genotypes in the strains that isolated from the same wards proposed endogenous routes of the infection, as common cause of CDI in these patients.

Effects of Cultivating Years on Survival of Culturable Escherichia coli O157:H7 in Greenhouse Soils

The extent to how Escherichia coli O157:H7 can survive in soil and the predominant factors that determine its survival are crucial issues from a public health point of view. This study investigated the survival of E. coli O157:H7 in vegetable soils in plastic-greenhouse cultivation over 0, 1, 4, 8, and 12 years in southern China. Results showed that the survival times ( t_d) calculated from the Weibull model for the five tested soils ranged from 9.00 to 21.11 days. In general, E. coli O157:H7 survived longer in open-field soils than in greenhouse soils under the same incubation conditions. The t_d values were greater in soils with a lower level of electrical conductivity, a higher level of total nitrogen, and a higher level of sand content. Compared to other factors, electrical conductivity was the most important factor affecting the survival of E. coli O157:H7 in the tested soils. Different survival times of E. coli O157:H7 in vegetable soils under diverse cultivation patterns highlight the importance of preventing pathogenic contamination for the purpose of food safety.

The Opp (AmiACDEF) Oligopeptide Transporter Mediates Resistance of Serotype 2 Streptococcus pneumoniae D39 to Killing by Chemokine CXCL10 and Other Antimicrobial Peptides

Antimicrobial peptides (AMPs), including chemokines, are produced during infections to kill pathogenic bacteria. To fill in gaps in knowledge about the sensitivities of Streptococcus pneumoniae and related Streptococcus species to chemokines and AMPs, we performed a systematic, quantitative study of inhibition by chemokine CXCL10 and the AMPs LL-37 and nisin. In a standard Tris-glucose buffer (TGS), all strains assayed lacked metabolic activity, as determined by resazurin (alamarBlue) reduction, and were extremely sensitive to CXCL10 and AMPs (50% inhibitory concentration [IC₅₀], ∼0.04 μM). In TGS, changes in sensitivities caused by mutations were undetectable. In contrast, strains that retained reductive metabolic activity in a different assay buffer (NPB [10 mM sodium phosphate {pH 7.4}, 1% {vol/vol} brain heart infusion {BHI} broth]) were less sensitive to CXCL10 and AMPs than in TGS. In NPB, mutants known to respond to AMPs, such as Δdlt mutants lacking d-alanylation of teichoic acids, exhibited the expected increased sensitivity. S. pneumoniae serotype 2 strain D39 was much (∼10-fold) less sensitive to CXCL10 killing in NPB than serotype 4 strain TIGR4, and the sensitivity of TIGR4 was unaffected by the absence of capsule. Candidate screening of strain D39 revealed that mutants lacking Opp (ΔamiACDEF) oligopeptide permease were significantly more resistant to CXCL10 than the wild-type strain. This increased resistance could indicate that Opp is a target for CXCL10 binding or that it transports CXCL10 into cells. Finally, ΔftsX or ΔftsE mutants of Bacillus subtilis or amino acid changes that interfere with FtsX function in S. pneumoniae did not impart resistance to CXCL10, in contrast to previous results for Bacillus anthracis, indicating that FtsX is not a general target for CXCL10 binding.IMPORTANCES. pneumoniae (pneumococcus) is a human commensal bacterium and major opportunistic respiratory pathogen that causes serious invasive diseases, killing millions of people worldwide annually. Because of its increasing antibiotic resistance, S. pneumoniae is now listed as a "superbug" for which new antibiotics are urgently needed. This report fills in knowledge gaps and resolves inconsistencies in the scientific literature about the sensitivity of S. pneumoniae and related Streptococcus pathogens to chemokines and AMPs. It also reveals a new mechanism by which S. pneumoniae can acquire resistance to chemokine CXCL10. This mechanism involves the Opp (AmiACDEF) oligopeptide transporter, which plays additional pleiotropic roles in pneumococcal physiology, quorum sensing, and virulence. Taking the results together, this work provides new information about the way chemokines kill pneumococcal cells.

The DinJ/RelE Toxin-Antitoxin System Suppresses Bacterial Proliferation and Virulence of Xylella fastidiosa in Grapevine

Xylella fastidiosa, the causal agent of Pierce's disease of grapes, is a slow-growing, xylem-limited, bacterial pathogen. Disease progression is characterized by systemic spread of the bacterium through xylem vessel networks, causing leaf-scorching symptoms, senescence, and vine decline. It appears to be advantageous to this pathogen to avoid excessive blockage of xylem vessels, because living bacterial cells are generally found in plant tissue with low bacterial cell density and minimal scorching symptoms. The DinJ/RelE toxin-antitoxin system is characterized here for a role in controlling bacterial proliferation and population size during plant colonization. The DinJ/RelE locus is transcribed from two separate promoters, allowing for coexpression of antitoxin DinJ with endoribonuclease toxin RelE, in addition to independent expression of RelE. The ratio of antitoxin/toxin expressed is dependent on bacterial growth conditions, with lower amounts of antitoxin present under conditions designed to mimic grapevine xylem sap. A knockout mutant of DinJ/RelE exhibits a hypervirulent phenotype, with higher bacterial populations and increased symptom development and plant decline. It is likely that DinJ/RelE acts to prevent excessive population growth, contributing to the ability of the pathogen to spread systemically without completely blocking the xylem vessels and increasing probability of acquisition by the insect vector.

A High-Throughput Screening Platform of Microbial Natural Products for the Discovery of Molecules with Antibiofilm Properties against Salmonella

In this report, we describe a High-Throughput Screening (HTS) to identify compounds that inhibit biofilm formation or cause the disintegration of an already formed biofilm using the Salmonella Enteritidis 3934 strain. Initially, we developed a new methodology for growing Salmonella biofilms suitable for HTS platforms. The biomass associated with biofilm at the solid-liquid interface was quantified by staining both with resazurin and crystal violet, to detect living cells and total biofilm mass, respectively. For a pilot project, a subset of 1120 extracts from the Fundación MEDINA's collection was examined to identify molecules with antibiofilm activity. This is the first validated HTS assay of microbial natural product extracts which allows for the detection of four types of activities which are not mutually exclusive: inhibition of biofilm formation, detachment of the preformed biofilm and antimicrobial activity against planktonic cells or biofilm embedded cells. Currently, several extracts have been selected for further fractionation and purification of the active compounds. In one of the natural extracts patulin has been identified as a potent molecule with antimicrobial activity against both, planktonic cells and cells within the biofilm. These findings provide a proof of concept that the developed HTS can lead to the discovery of new natural compounds with antibiofilm activity against Salmonella and its possible use as an alternative to antimicrobial therapies and traditional disinfectants.

Visualization of the Charcoal Agar Resazurin Assay for Semi-quantitative, Medium-throughput Enumeration of Mycobacteria

There is an urgent need to discover and progress anti-infectives that shorten the duration of tuberculosis (TB) treatment. Mycobacterium tuberculosis, the etiological agent of TB, is refractory to rapid and lasting chemotherapy due to the presence of bacilli exhibiting phenotypic drug resistance. The charcoal agar resazurin assay (CARA) was developed as a tool to characterize active molecules discovered by high-throughput screening campaigns against replicating and non-replicating M. tuberculosis. Inclusion of activated charcoal in bacteriologic agar medium helps mitigate the impact of compound carry-over, and eliminates the requirement to pre-dilute cells prior to spotting on CARA microplates. After a 7-10 day incubation period at 37 °C, the reduction of resazurin by mycobacterial microcolonies growing on the surface of CARA microplate wells permits semi-quantitative assessment of bacterial numbers via fluorometry. The CARA detects approximately a 2-3 log₁₀ difference in bacterial numbers and predicts a minimal bactericidal concentration leading to ≥99% bacterial kill (MBC_≥99). The CARA helps determine whether a molecule is active on bacilli that are replicating, non-replicating, or both. Pilot experiments using the CARA facilitate the identification of which concentration of test agent and time of compound exposure require further evaluation by colony forming unit (CFU) assays. In addition, the CARA can predict if replicating actives are bactericidal or bacteriostatic.

Characterization in Helicobacter pylori of a Nickel Transporter Essential for Colonization That Was Acquired during Evolution by Gastric Helicobacter Species

Metal acquisition is crucial for all cells and for the virulence of many bacterial pathogens. In particular, nickel is a virulence determinant for the human gastric pathogen Helicobacter pylori as it is the cofactor of two enzymes essential for in vivo colonization, urease and a [NiFe] hydrogenase. To import nickel despite its scarcity in the human body, H. pylori requires efficient uptake mechanisms that are only partially defined. Indeed, alternative ways of nickel entry were predicted to exist in addition to the well-described NixA permease. Using a genetic screen, we identified an ABC transporter, that we designated NiuBDE, as a novel H. pylori nickel transport system. Unmarked mutants carrying deletions of nixA, niuD and/or niuB, were constructed and used to measure (i) tolerance to toxic nickel exposure, (ii) intracellular nickel content by ICP-OES, (iii) transport of radioactive nickel and (iv) expression of a reporter gene controlled by nickel concentration. We demonstrated that NiuBDE and NixA function separately and are the sole nickel transporters in H. pylori. NiuBDE, but not NixA, also transports cobalt and bismuth, a metal currently used in H. pylori eradication therapy. Both NiuBDE and NixA participate in nickel-dependent urease activation at pH 5 and survival under acidic conditions mimicking those encountered in the stomach. However, only NiuBDE is able to carry out this activity at neutral pH and is essential for colonization of the mouse stomach. Phylogenomic analyses indicated that both nixA and niuBDE genes have been acquired via horizontal gene transfer by the last common ancestor of the gastric Helicobacter species. Our work highlights the importance of this evolutionary event for the emergence of Helicobacter gastric species that are adapted to the hostile environment of the stomach where the capacity of Helicobacter to import nickel and thereby activate urease needs to be optimized.

Differentiation of Human U937 Promonocytic Cells is Impaired by Moderate Copper Deficiency

Copper (Cu) deficiency suppresses macrophage activities in animals and humans. Our previous studies indicated that the Induction of Cu deficiency in differentiated U937 monocytic cells impairs respiratory burst and bactericidal activities and lipopolysaccharide-mediated secretion of inflammatory mediators. The current investigation examined the roles of Cu in the monocytic differentiation process. Human U937 promonocytic cells were exposed to a high affinity Cu chelator (5 µM 2,3,2-tetraamine [tet]) for 24 hr before inducing differentiation by treatment with 1,25-dihydroxyvitamin D3 plus Interferon-γ (DI). This procedure decreased cell Cu by 55% without compromising cellular Zn, Fe, or general metabolic activities. Lower Cu status significantly attenuated the expression of maturation markers Mac-1 (CD11b), ICAM-1 (CD54), and LPS-R (CD14). This change was associated with a marked suppression in respiratory burst activity and killing of Salmonella. To examine if the adverse effect of inadequate Cu on the DI-induced differentiation represented a more general defect, U937 cells were treated with phorbol 12-myrlstate 13-acetate (PMA). Lower Cu status also suppressed PMA-mediated differentiation of U937 cells. Supplemental Cu, but not Zn or Fe, blocked the tet-induced declines in cell Cu, expression of maturation markers, and respiratory burst and bactericidal activities. These results demonstrate that Cu is essential for the monocytic differentiation process that contributes to the competency of the host's defense system.

An Investigation into the Immunomodulatory Activities of Sutherlandia frutescens in Healthy Mice

Sutherlandia frutescens is a medicinal plant that has been traditionally used in southern Africa for cancers, infections, and inflammatory conditions. We recently published experiments demonstrating that an aqueous extract of S. frutescens possessed potent immune-stimulatory activity. This work was carried out with murine macrophages, an immune cell type that plays a pivotal role in host defense from infection and in shaping host inflammatory and immune responses. Here, we conducted a series of follow-up experiments to explore the impact of consuming S. frutescens on host response to bacterial challenge using healthy mice. We found that feeding mice a diet containing S. frutescens failed to significantly alter host response to systemic infection by either a gram-positive or gram-negative bacterium (i.e., L. monocytogenes and E. coli, respectively). In contrast to the in vitro observations, we found no evidence that S. frutescens consumption stimulated in vivo inflammatory responses; instead, consumption of S. frutescens tended to diminish in vivo inflammatory responses. Several possible reasons for this are discussed.

Real-time assessment of Streptococcus mutans biofilm metabolism on resin composite

OBJECTIVE

The release of unpolymerized monomers and by-products of resin composites influences biofilm growth and confounds the measurement of metabolic activity. Current assays to measure biofilm viability have critical limitations and are typically not performed on relevant substrates. The objective of the present study was to determine the utility of firefly luciferase assay for quantification of the viability of intact biofilms on a resin composite substrate, and correlate the results with a standard method (viable colony counts).

METHODS

Disk-shaped specimens of a dental resin composite were fabricated, wet-polished, UV-sterilized, and stored in water. Biofilms of Streptococcus mutans (strain UA159 modified by insertion of constitutively expressed firefly luc gene) were grown (1:500 dilution; anaerobic conditions, 24h, 37°C) in two media concentrations (0.35x and 0.65x THY medium supplemented with 0.1% sucrose; n=15/group). An additional group of specimens with biofilms grown in 0.65x+sucrose media was treated with chlorhexidine gluconate solution to serve as the control group. Bioluminescence measurements of non-disrupted biofilms were obtained after addition of d-Luciferin substrate. The adherent biofilms were removed by sonication, and bioluminescence of sonicated bacteria was then measured. Viable colony counts were performed after plating sonicated bacteria on THY agar plates supplemented with spectinomycin. Bioluminescence values and cell counts were correlated using Spearman correlation tests (α=0.05).

RESULTS

Strong positive correlations between viable colony counts and bioluminescence values, both before- and after-sonication, validated the utility of this assay.

SIGNIFICANCE

A novel non-disruptive, real-time bioluminescence assay is presented for quantification of intact S. mutans biofilms grown on a resin composite, and potentially on antibacterial materials and other types of dental biomaterials.

Antibacterial and anti-biofilm activity of mouthrinses containing cetylpyridinium chloride and sodium fluoride

Background

Cetylpyridinium chloride (CPC) and sodium fluoride augment oral hygiene by inactivating bacteria and inhibiting enamel demineralisation, respectively. However, there are few reports in the literature documenting the antibacterial efficacy of their combined use in mouthrinses. We have used six experimental systems to compare the antibacterial effects of mouthrinses containing 0.075 % CPC (test rinse, TR) or 0.075 % CPC with sodium fluoride (test fluoride rinse, TFR).

Results

Effects against planktonic bacteria were determined using viable counting (for Streptococcus mutans and salivary bacteria), a redox dye (for Actinomyces viscosus and salivary bacteria) and viable counting (for ex vivo oral rinses). Effects against saliva-derived biofilms were quantified using confocal microscopy and differential viable counting. Inhibition of biofilm formation was evaluated by pre-treating hydroxyapatite coupons with mouthrinses prior to inoculation. Otherwise-identical controls without CPC (control rinse and control fluoride rinse, CR and CFR, respectively), were included throughout. Compared to the controls, TFR and TR demonstrated significant antimicrobial effects in the redox assays, by viable counts (>3 log reductions) and in oral rinse samples (>1.25 log reductions, p < 0.05). TFR and TR also significantly reduced the viability of oral biofilms. Pre-treatment of hydroxyapatite with TFR and TR significantly inhibited biofilm formation (>3 log difference, p < 0.05). Overall, there were no consistent differences in the activities of TR and TFR.

Conclusions

Sodium fluoride did not influence the antibacterial and anti-biofilm potency of CPC-containing formulations, supporting the combined use of CPC and sodium fluoride in mouthrinses to control oral bacteria and protect tooth enamel.

Rapid, Semiquantitative Assay To Discriminate among Compounds with Activity against Replicating or Nonreplicating Mycobacterium tuberculosis

The search for drugs that can kill replicating and nonreplicating Mycobacterium tuberculosis faces practical bottlenecks. Measurement of CFU and discrimination of bacteriostatic from bactericidal activity are costly in compounds, supplies, labor, and time. Testing compounds against M. tuberculosis under conditions that prevent the replication of M. tuberculosis often involves a second phase of the test in which conditions are altered to permit the replication of bacteria that survived the first phase. False-positive determinations of activity against nonreplicating M. tuberculosis may arise from carryover of compounds from the nonreplicating stage of the assay that act in the replicating stage. We mitigate these problems by carrying out a 96-well microplate liquid MIC assay and then transferring an aliquot of each well to a second set of plates in which each well contains agar supplemented with activated charcoal. After 7 to 10 days—about 2 weeks sooner than required to count CFU—fluorometry reveals whether M. tuberculosis bacilli in each well have replicated extensively enough to reduce a resazurin dye added for the final hour. This charcoal agar resazurin assay (CARA) distinguishes between bacterial biomasses in any two wells that differ by 2 to 3 log₁₀ CFU. The CARA thus serves as a pretest and semiquantitative surrogate for longer, more laborious, and expensive CFU-based assays, helps distinguish bactericidal from bacteriostatic activity, and identifies compounds that are active under replicating conditions, nonreplicating conditions, or both. Results for 14 antimycobacterial compounds, including tuberculosis (TB) drugs, revealed that PA-824 (pretomanid) and TMC207 (bedaquiline) are largely bacteriostatic.

Bioprospecting the American alligator (Alligator mississippiensis) host defense peptidome

Cationic antimicrobial peptides and their therapeutic potential have garnered growing interest because of the proliferation of bacterial resistance. However, the discovery of new antimicrobial peptides from animals has proven challenging due to the limitations associated with conventional biochemical purification and difficulties in predicting active peptides from genomic sequences, if known. As an example, no antimicrobial peptides have been identified from the American alligator, Alligator mississippiensis, although their serum is antimicrobial. We have developed a novel approach for the discovery of new antimicrobial peptides from these animals, one that capitalizes on their fundamental and conserved physico-chemical properties. This sample-agnostic process employs custom-made functionalized hydrogel microparticles to harvest cationic peptides from biological samples, followed by de novo sequencing of captured peptides, eliminating the need to isolate individual peptides. After evaluation of the peptide sequences using a combination of rational and web-based bioinformatic analyses, forty-five potential antimicrobial peptides were identified, and eight of these peptides were selected to be chemically synthesized and evaluated. The successful identification of multiple novel peptides, exhibiting antibacterial properties, from Alligator mississippiensis plasma demonstrates the potential of this innovative discovery process in identifying potential new host defense peptides.

Screening the toxicity and biodegradability of petroleum hydrocarbons by a rapid colorimetric method

Crude oil and petroleum products have a wide variety of hazardous components with high toxicity and low biodegradability. Certain dyes change their colors by intercepting electron transfer reactions during the transformation processes. This study applied resazurin and 2,6-dichlorophenol-indophenol indicators for a rapid screening biodegradation capability and toxicity response to various petroleum products such as motor oil, diesel, gasoline, and phenol. Colorimetry tests were performed in test tubes, and the absorbance values were measured over time. We observed different discoloration profiles after degradation tests using Bacillus subtilis inoculum. Phytotoxicity assays were also performed to compare colorimetric screening assays with a conventional toxicity testing with plants (seed germination). The results indicated that biotransformation of oils can increase its overall toxicity. Intermediate byproducts can be formed through biodegradation and thereby increase the toxicity of oils. The assessment of acute toxicity has shown that phenol is extremely toxic to petroleum-biodegrading microbial communities. Low molecular-weight gasoline was considered biodegradable, but it also exhibited a high acute toxic effect, mainly due to its high solubility and the presence of more volatile compounds that can penetrate cells and potentially damage cellular structures.

Pioglitazone restores phagocyte mitochondrial oxidants and bactericidal capacity in chronic granulomatous disease

BACKGROUND

Deficient production of reactive oxygen species (ROS) by the phagocyte nicotinamide adenine dinucleotide (NADPH) oxidase in patients with chronic granulomatous disease (CGD) results in susceptibility to certain pathogens secondary to impaired oxidative killing and mobilization of other phagocyte defenses. Peroxisome proliferator-activated receptor (PPAR) γ agonists, including pioglitazone, approved for type 2 diabetes therapy alter cellular metabolism and can heighten ROS production. It was hypothesized that pioglitazone treatment of gp91(phox-/-) mice, a murine model of human CGD, would enhance phagocyte oxidant production and killing of Staphylococcus aureus, a significant pathogen in patients with this disorder.

OBJECTIVES

We sought to determine whether pioglitazone treatment of gp91(phox-/-) mice enhanced phagocyte oxidant production and host defense.

METHODS

Wild-type and gp91(phox-/-) mice were treated with the PPARγ agonist pioglitazone, and phagocyte ROS and killing of S aureus were investigated.

RESULTS

As demonstrated by 3 different ROS-sensing probes, short-term treatment of gp91(phox-/-) mice with pioglitazone enhanced stimulated ROS production in neutrophils and monocytes from blood and neutrophils and inflammatory macrophages recruited to tissues. Mitochondria were identified as the source of ROS. Findings were replicated in human monocytes from patients with CGD after ex vivo pioglitazone treatment. Importantly, although mitochondrial (mt)ROS were deficient in gp91(phox-/-) phagocytes, their restoration with treatment significantly enabled killing of S aureus both ex vivo and in vivo.

CONCLUSIONS

Together, the data support the hypothesis that signaling from the NADPH oxidase under normal circumstances governs phagocyte mtROS production and that such signaling is lacking in the absence of a functioning phagocyte oxidase. PPARγ agonism appears to bypass the need for the NADPH oxidase for enhanced mtROS production and partially restores host defense in CGD.

Covalent modification of a ten-residue cationic antimicrobial peptide with levofloxacin

The rampant spread of antibiotic resistant bacteria has spurred interest in alternative strategies for developing next-generation antibacterial therapies. As such, there has been growing interest in cationic antimicrobial peptides (CAMPs) and their therapeutic applications. Modification of CAMPs via conjugation to auxiliary compounds, including small molecule drugs, is a new approach to developing effective, broad-spectrum antibacterial agents with novel physicochemical properties and versatile antibacterial mechanisms. Here, we've explored design parameters for engineering CAMPs conjugated to small molecules with favorable physicochemical and antibacterial properties by covalently affixing a fluoroquinolone antibiotic, levofloxacin, to the ten-residue CAMP Pep-4. Relative to the unmodified Pep-4, the conjugate was found to demonstrate substantially increased antibacterial potency under high salt concentrations. Historically, it has been observed that most CAMPs lose antibacterial effectiveness in such high ionic strength environments, a fact that has presented a challenge to their development as therapeutics. Physicochemical studies revealed that P4LC was more hydrophobic than Pep-4, while mechanistic findings indicated that the conjugate was more effective at disrupting bacterial membrane integrity. Although the inherent antibacterial effect of the incorporated levofloxacin molecules did not appear to be substantially realized in this conjugate, these findings nevertheless suggest that covalent attachment of small molecule antibiotics with favorable physicochemical properties to CAMPs could be a promising strategy for enhancing peptide performance and overall therapeutic potential. These results have broader applicability to the development of future CAMP-antibiotic conjugates for potential therapeutic applications.

Carbon and clay nanoparticles induce minimal stress responses in gram negative bacteria and eukaryotic fish cells

We investigated in vitro the potential mutagenic and toxic effects of two clay-based nanoparticles, Cloisite® Na(+) (Cloisite) and halloysite; and multi-walled carbon nanotubes (MWCNT), commonly used in the polymer composite industry. Using the Ames test, the three nanoparticles did not have a true mutagenic effect, although growth of Salmonella enterica var. Typhimurium (S.typhimurium) was diminished at higher nanoparticle concentrations. We investigated the impact of nanoparticles on Escherichia coli and S. typhimurium including oxyR and rpoS mutants, which are susceptible to oxidative stress. The oxyR mutants were inhibited in the presence of nanoparticles, when grown aerobically with light. Toxicity was not observed in the absence of light or during anaerobic growth. E. coli rpoS mutants exhibited some toxicity when cultured with Cloisite and MWCNT only when grown aerobically with light. There was no effect with other nanoparticles, or with S. typhimurium rpoS mutants. MWCNT exhibited a slight toxic effect against Epithelioma papulosum cyprini (EPC) cells only at the highest concentration tested. There was no discernable toxicity to EPC cells caused by the clay nanoparticles. We conclude that clay-based nanoparticles and MWCNT do not exert a mutagenic effect and do not have a general toxic effect across all bacterial species or between prokaryotic and eukaryotic cells. Modest toxicity was only observed in eukaryotic EPC cells against MWCNT at the highest concentration tested. Limited species-specific toxicity to clay based and MWCNT nanoparticles was seen in bacterial strains primarily due to culture conditions and mutations that exacerbate oxidative stress.

The antibacterial effect of ethanol extract of polish propolis on mutans streptococci and lactobacilli isolated from saliva

Dental caries occurrence is caused by the colonization of oral microorganisms and accumulation of extracellular polysaccharides synthesized by Streptococcus mutans with the synergistic influence of Lactobacillus spp. bacteria. The aim of this study was to determine ex vivo the antibacterial properties of ethanol extract of propolis (EEP), collected in Poland, against the main cariogenic bacteria: salivary mutans streptococci and lactobacilli. The isolation of mutans streptococci group bacteria (MS) and Lactobacillus spp. (LB) from stimulated saliva was performed by in-office CRT bacteria dip slide test. The broth diffusion method and AlamarBlue assay were used to evaluate the antimicrobial activity of EEP, with the estimation of its minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC). The biochemical composition of propolis components was assessed. The mean MIC and MBC values of EEP, in concentrations ranging from 25 mg/mL to 0.025 mg/mL, for the MS and LB were found to be 1.10 mg/mL versus 0.7 mg/mL and 9.01 mg/mL versus 5.91 mg/mL, respectively. The exposure to an extract of Polish propolis affected mutans streptococci and Lactobacillus spp. viability, exhibiting an antibacterial efficacy on mutans streptococci group bacteria and lactobacilli saliva residents, while lactobacilli were more susceptible to EEP. Antibacterial measures containing propolis could be the local agents acting against cariogenic bacteria.

Cellular glutathione plays a key role in copper uptake mediated by human copper transporter 1

Copper is an essential micronutrient. Following entry via the human copper transporter 1 (hCTR1), copper is delivered to several copper chaperones, which subsequently transfer the metal to specific targets via protein:protein interactions. It is has been assumed, but not demonstrated, that chaperones acquire copper directly from hCTR1. However, some reports have pointed to an intermediary role for glutathione (GSH), an abundant copper-binding tri-peptide. To address the issue of how transported copper is acquired by the copper chaperones in vivo, we measured the initial rate of (64)Cu uptake in cells in which the cellular levels of copper chaperones or GSH were substantially depleted or elevated. Knockdown or overexpression of copper chaperones ATOX1, CCS, or both had no effect on the initial rate of (64)Cu entry into HEK293 cells having endogenous or overexpressed hCTR1. In contrast, depleting cellular GSH using L-buthionine-sulfoximine (BSO) caused a 50% decrease in the initial rate of (64)Cu entry in HEK293 cells and other cell types. This decrease was reversed by washout of BSO or GSH replenishment with a permeable ester. BSO treatment under our experimental conditions had no significant effects on the viability, ATP levels, or metal content of the cells. Attenuated (64)Cu uptake in BSO was not due to oxidation of the cysteine in the putative metal-binding motif (HCH) at the intracellular hCTR1 COOH terminus, because a mutant lacking this motif was fully active, and (64)Cu uptake was still reduced by BSO treatment. Our data suggest that GSH plays an important role in copper handling at the entry step.

Molecular typing and characterization of nasal carriage and community-onset infection methicillin-susceptible Staphylococcus aureus isolates in two Taiwan medical centers

Background

Compared to methicillin-resistant Staphylococcus aureus (MRSA), characteristics of nasal carriage and community-onset infection methicillin-susceptible S. aureus (MSSA) are less well known. No characteristics of MSSA in Taiwan have been reported previously.

Methods

We analyzed 100 nasal carriage and 34 community-onset infection MSSA isolates by pulsed-field gel electrophoresis (PFGE), spa typing, multi-locus sequence typing, agr typing, virulence gene detection, growth rate measurement, and antimicrobial susceptibility.

Results

In PFGE analysis, most (68%) infection isolates could be grouped in one major cluster using a 70% similarity cutoff. In contrast, only 17% of nasal carriage isolates belonged to this cluster. A similar classification was obtained using Based Upon Repeat Pattern analysis of spa types. The MSSA infection isolates cluster was closely related to the virulent clones of clonal complex 1 (CC1), which includes strains MW2 (USA400) and MSSA476. ST188 of CC1 was the predominant clone detected for community-onset MSSA infections. The only common ST type for MSSA and MRSA in Taiwan was ST59, the community-associated MRSA clone. It is likely, therefore, that MRSA originated from MSSA clones through SCCmec transfer. Compared to nasal carriage isolates, infection isolates less frequently possessed egc, tst and hlg genes, were more commonly susceptible to erythromycin (91% vs. 54%), and had shorter mean doubling times (38 min vs. 55 min).

Conclusions

The clonal lineages of MSSA nasal carriage and infection isolates differed in our sample of Taiwan isolates. Most community-onset MSSA infections resulted from relatively few clonal lineages. Nasal carriage isolates more frequently possessed the egc, tst and hlg genes, were more resistant to erythromycin, and grew more slowly.

Nocardia brasiliensis cell wall lipids modulate macrophage and dendritic responses that favor development of experimental actinomycetoma in BALB/c mice

Nocardia brasiliensis is a Gram-positive facultative intracellular bacterium frequently isolated from human actinomycetoma. However, the pathogenesis of this infection remains unknown. Here, we used a model of bacterial delipidation with benzine to investigate the role of N. brasiliensis cell wall-associated lipids in experimental actinomycetoma. Delipidation of N. brasiliensis with benzine resulted in complete abolition of actinomycetoma without affecting bacterial viability. Chemical analyses revealed that trehalose dimycolate and an unidentified hydrophobic compound were the principal compounds extracted from N. brasiliensis with benzine. By electron microscopy, the extracted lipids were found to be located in the outermost membrane layer of the N. brasiliensis cell wall. They also appeared to confer acid-fastness. In vitro, the extractable lipids from the N. brasiliensis cell wall induced the production of the proinflammatory cytokines interleukin-1β (IL-1β), IL-6, and CCL-2 in macrophages. The N. brasiliensis cell wall extractable lipids inhibited important macrophage microbicidal effects, such as tumor necrosis factor alpha (TNF-α) and nitric oxide (NO) production, phagocytosis, bacterial killing, and major histocompatibility complex class II (MHC-II) expression in response to gamma interferon (IFN-γ). In dendritic cells (DCs), N. brasiliensis cell wall-associated extractable lipids suppressed MHC-II, CD80, and CD40 expression while inducing tumor growth factor β (TGF-β) production. Immunization with delipidated N. brasiliensis induced partial protection preventing actinomycetoma. These findings suggest that N. brasiliensis cell wall-associated lipids are important for actinomycetoma development by inducing inflammation and modulating the responses of macrophages and DCs to N. brasiliensis.

Photodynamic therapy as an alternative treatment for disinfection of bacteria in oral biofilms

BACKGROUND AND OBJECTIVES

Biofilm-related diseases such as caries and periodontal disease are prevalent chronic oral infections which pose significant oral and general health risks. Biofilms are sessile communities attached to surfaces. Photodynamic therapy (PDT) has been demonstrated to have a significant anti-microbial effect and presents as an alternative to treating biofilm-related disease. The aim of this study was to determine the ability of porfimer sodium induced PDT to treat localized infections of Streptococcus mutans in biofilm communities.

MATERIALS AND METHODS

Reproducible biofilms were formed by S. mutans strain ATCC 27351 growing in log phase at 37°C in Brain Heart Infusion medium, circulating through flow cells at 3 ml/minute for 36-48 hours. The photosensitizer used was porfimer sodium (Photofrin®) at 125 µg/ml with biofilm immersion times of 5 minutes and increasing energy density of post-immersion laser illumination at 630 nm (100 mW/cm(2) ). Resulting effects on bacterial viability in the biofilms were tracked by monitoring alamarBlue® conversion. Supplementary data characterizing the biofilms before and after exposure to PDT were acquired by Multiple Attenuated Internal Reflection Infrared Spectroscopy (MAIR-IR).

RESULTS

The results of this study show that PDT using porfimer sodium and 630 nm laser light was effective in significantly reducing the viability of S. mutans biofilms. Maximum effectiveness was seen when biofilms were exposed to both photosensitizer and light versus controls. Porfimer sodium incubation times as short as 5 minutes in solutions as dilute as 25 µg/ml and illuminated with as little as 30 J/cm(2) resulted in significant decreases in viability of bacteria in biofilms. Optimum parameters appear to be 125 µg/ml porfimer sodium concentration and incubated for 5 minutes and 60 J/cm(2) of light energy density.

CONCLUSIONS

This study has demonstrated that significant killing of the cariogenic organism S. mutans by the combination of a photosensitizer and the appropriate wavelength of laser light was possible even when the bacteria are embedded in an extracellular matrix.

Quantification of initial adhesion of Enterococcus faecalis to medical grade polymers using a DNA-based fluorescence assay

This paper reports on the use of a DNA-based fluorescence assay to study and quantify the initial interactions of the uropathogen Enterococcus faecalis with different polymers commonly used for the fabrication of medical devices and implants, including polyurethane (PU), silicone (SI), high-density polyethylene (HDPE), polyamide (PA), poly(methyl methacrylate) (PMMA) and polytetrafluoroethylene (PTFE). To follow the kinetics of E. faecalis adhesion, polymer samples were incubated in bacterial solution for various times and the relative concentration of adhered bacteria was obtained using two methods: commonly used CFU plate counting and a DNA quantification assay. Results obtained from DNA-based fluorescence assays showed that E. faecalis adhesion on PU is 3-times higher than that on PTFE following exposure to bacteria for 180 min. Neither surface wettability nor surface roughness of the studied polymers was found to correlate with E. faecalis adhesion, suggesting the involvement of much more complex adhesion mechanisms of bacteria onto surfaces. SEM micrographs of adhered bacteria illustrated that adhesion was different depending on the type of polymeric substrate: adhesion on PU samples was characterized by the aggregation of bacterial cells in dense clusters, as well as by the presence of fimbriae between cells and the substrate, which could explain the high adhesion to PU compared to the other polymers. This work demonstrated that the bacterial adhesion to polymers occurs at an early stage of the contact and suggests that the initial adhesion stage should be controlled, in order to prevent subsequent biofilm formation and, thus, reduce the risk of implant-associated infections.

Bacteria-specific neutrophil dysfunction associated with interferon-stimulated gene expression in the acute respiratory distress syndrome

Acute respiratory distress syndrome (ARDS) is a poorly understood condition with greater than 30% mortality. Massive recruitment of neutrophils to the lung occurs in the initial stages of the ARDS. Significant variability in the severity and duration of ARDS-associated pulmonary inflammation could be linked to heterogeneity in the inflammatory capacity of neutrophils. Interferon-stimulated genes (ISGs) are a broad gene family induced by Type I interferons. While ISGs are central to anti-viral immunity, the potential exists for these genes to evoke extensive modification in cellular response in other clinical settings. In this prospective study, we sought to determine if ISG expression in circulating neutrophils from ARDS patients is associated with changes in neutrophil function. Circulating neutrophil RNA was isolated, and hierarchical clustering ranked patients' expression of three ISGs. Neutrophil response to pathogenic bacteria was compared between normal and high ISG-expressing neutrophils. High neutrophil ISG expression was found in 25 of 95 (26%) of ARDS patients and was associated with reduced migration toward interleukin-8, and altered responses to Staphylococcus aureus, but not Pseudomonas aeruginosa, which included decreased p38 MAP kinase phosphorylation, superoxide anion release, interleukin-8 release, and a shift from necrotic to apoptotic cell death. These alterations in response were reflected in a decreased capacity to kill S. aureus, but not P. aeruginosa. Therefore, the ISG expression signature is associated with an altered circulating neutrophil response phenotype in ARDS that may predispose a large subgroup of patients to increased risk of specific bacterial infections.

Human IgG isotypes and activating Fcγ receptors in the interaction of Salmonella enterica serovar Typhimurium with phagocytic cells

Several classes and multiple subclasses of immunoglobulins are produced towards protein and polysaccharide antigens in response to Salmonella infection and play a key role in protection against systemic disease. The targeting of Salmonella to Fc receptors (FcR) on phagocytes is a key step in the antibody-mediated antibacterial functions of host cells. We wished to compare the relative efficiency of different human IgG subclasses, which targeted the Salmonella enterica OmpA surface protein in modulating the interaction of bacteria with human phagocytes. To this end, we developed a novel system by tagging OmpA with a foreign CD52 mimotope (TSSPSAD) and opsonizing the bacteria with a panel of humanized CD52 antibodies that share the same antigen-binding V-region, but have constant regions of different subclasses. Our data revealed that opsonization with all the IgG subclasses increases Salmonella uptake by human phagocytes. IgG3 resulted in the highest level of bacterial uptake and the highest average bacterial load per infected cell, which was closely followed by IgG1, then IgG4 and lastly IgG2. Phagocytosis mediated by IgG1, IgG3 and IgG4 had a higher dependency on FcγRI than FcγRIIA, whereas IgG2-mediated phagocytosis required FcγRIIA more than FcγRI. The results show that IgG binding to OmpA increases the uptake of Salmonella by human phagocytic cells and that the efficiency of this process depends both on the subclass of the IgG and the type of FcR that is available for antibody binding.

Resazurin metabolism assay for root canal disinfectant evaluation on dual-species biofilms

INTRODUCTION

Endodontic infections are caused by polymicrobial biofilms. Therefore, novel root canal disinfectants should be evaluated not only on single-species biofilms but also on dual- or mixed-species biofilms. A simple, high-throughput assay is urgently needed for this. In this study, the application of the resazurin metabolism assay was investigated for the evaluation of a root canal disinfectant on dual-species biofilms.

METHODS

Enterococcus faecalis with or without Streptococcus mutans in biofilms were formed in an active attachment biofilm model for 24 hours. Subsequently, the biofilms were treated with various concentrations of NaOCl for 1 minute. After resazurin metabolism by both organisms was confirmed, treatment efficacies using 0.0016% resazurin were evaluated.

RESULTS

During NaOCl treatments, resazurin metabolism displays a clear dose response, not only in single-species E. faecalis (or S. mutans) biofilms but also in dual-species biofilms. Notably, the assay revealed that the resistance of dual-species biofilms to NaOCl was 30-fold higher than in single-species E. faecalis biofilms. Viability counts on a selected NaOCl treatment (0.004%) confirmed this result and showed the increased resistance of E. faecalis in dual-species biofilms.

CONCLUSIONS

Clearly, the high-throughput and low cost resazurin metabolism assay has a great potential for testing novel root canal antimicrobial agents in mixed-species biofilms.

Oxidative and nitrosative responses of the chicken macrophage cell line MQ-NCSU to experimentalSalmonellainfection

Phagocytes limit replication or kill ingested organisms by producing toxic reactive oxygen and nitrogen species via NADPH oxidase and inducible nitric oxide synthase (iNOS). The present experiments were to investigate the production and the possible roles of superoxide, hydrogen peroxide (H2O2) and nitric oxide (NO) in the MQ-NCSU chicken macrophage cell line infected with Salmonella in vitro. After infection, intracellular Salmonella viable counts remained constant until 24 h post infection (PI) and started to decline from 48 h PI. Infection of cells with S. Typhimurium, S. Enteritidis and S. Gallinarum, as well as exposure to S. Enteritidis LPS induced low, but significant concentrations of superoxide 1 to 2 h PI, as determined by reduction of ferricytochrome c. There was no difference in superoxide production in infected cells and control cells after 4 h. Increased H2O2 was observed from cells infected with all the different Salmonella species between 2 and 3 h of infection. Nitrite was always greater in infected cells compared to uninfected cells at all times. However, Salmonella was not completely eliminated from the cells though these cells are capable of eliciting a noticeable oxidative burst response and great nitrosative responses, indicating that a strong oxidative burst (and other mechanism/s) is essential for the elimination of intracellular Salmonella.

The Alzheimer's disease-associated amyloid beta-protein is an antimicrobial peptide

Background

The amyloid β-protein (Aβ) is believed to be the key mediator of Alzheimer's disease (AD) pathology. Aβ is most often characterized as an incidental catabolic byproduct that lacks a normal physiological role. However, Aβ has been shown to be a specific ligand for a number of different receptors and other molecules, transported by complex trafficking pathways, modulated in response to a variety of environmental stressors, and able to induce pro-inflammatory activities.

Methodology/Principal Findings

Here, we provide data supporting an in vivo function for Aβ as an antimicrobial peptide (AMP). Experiments used established in vitro assays to compare antimicrobial activities of Aβ and LL-37, an archetypical human AMP. Findings reveal that Aβ exerts antimicrobial activity against eight common and clinically relevant microorganisms with a potency equivalent to, and in some cases greater than, LL-37. Furthermore, we show that AD whole brain homogenates have significantly higher antimicrobial activity than aged matched non-AD samples and that AMP action correlates with tissue Aβ levels. Consistent with Aβ-mediated activity, the increased antimicrobial action was ablated by immunodepletion of AD brain homogenates with anti-Aβ antibodies.

Conclusions/Significance

Our findings suggest Aβ is a hitherto unrecognized AMP that may normally function in the innate immune system. This finding stands in stark contrast to current models of Aβ-mediated pathology and has important implications for ongoing and future AD treatment strategies.

Activity of novel oxazolidinones against Nocardia brasiliensis growing within THP-1 macrophages

BACKGROUND

Nocardia are organisms that can escape the effects of both immune response and antimicrobial agents, due to their potential capacity to grow intracellularly. In previous studies, we found that experimental oxazolidinones, DA-7157 and DA-7218, are active both in vitro and in vivo.

OBJECTIVES

In this study, we compare the ability of linezolid, DA-7157 and DA-7218 to inhibit intracellular growth of Nocardia brasiliensis within the human monocyte cell line THP-1.

METHODS AND RESULTS

The addition of oxazolidinones to the infected macrophage monolayer at concentrations 0.25x, 1x, 4x and 16x the MIC for N. brasiliensis resulted in an inhibitory effect on bacterial growth as follows DA-7157 > or = DA-7218 > linezolid.

CONCLUSIONS

The excellent intracellular antimicrobial activity detected suggests that these compounds could be effective in the treatment of actinomycetoma. However, more studies are needed both in vitro and in vivo, including clinical trials, to confirm this issue.

Membrane-targeted synergistic activity of docosahexaenoic acid and lysozyme against Pseudomonas aeruginosa

Antimicrobial polypeptides, including lysozymes, have membrane perturbing activity and are well-documented effector molecules of innate immunity. In cystic fibrosis, a hereditary disease with frequent lung infection with Pseudomonas aeruginosa, the non-esterified fatty acid DA (docosahexaenoic acid), but not OA (oleic acid), is decreased, and DA supplementation has been shown to improve the clinical condition in these patients. We hypothesized that DA may, either alone or in conjunction with lysozyme, exert antibacterial action against Ps. aeruginosa. We found that DA and lysozyme synergistically inhibit the metabolic activity of Ps. aeruginosa, in contrast with OA. Electron microscopy and equilibrium dialysis suggest that DA accumulates in the bacterial membrane in the presence of lysozyme. Surface plasmon resonance with live bacteria and differential scanning calorimetry studies with bacterial model membranes reveal that, initially, DA facilitates lysozyme incorporation into the membrane, which in turn allows influx of more DA, leading to bacterial cell death. The present study elucidates a molecular basis for the synergistic action of non-esterified fatty acids and antimicrobial polypeptides, which may be dysfunctional in cystic fibrosis.

IL-17A is produced by Th17, gammadelta T cells and other CD4- lymphocytes during infection with Salmonella enterica serovar Enteritidis and has a mild effect in bacterial clearance

T(h)17 cells represent a new pro-inflammatory T(h) cell lineage distinct from T(h)1 and T(h)2 cells. T(h)17 cells have been shown to be involved in extracellular bacterial infection but their role in intracellular infection remains unclear. We found antigen-specific IL-17A production during a systemic infection of mice with the facultative intracellular bacterium Salmonella enterica serovar Enteritidis (S. Enteritidis) and examined the function and cellular source of IL-17A during the adaptive immune response to S. Enteritidis. Infected IL-17A-/- mice survived completely after inoculation with the highest infection dose found to be sub-lethal for wild-type (WT) C57BL/6 mice. However, at 20 and 80 days post-infection (d.p.i.), we repeatedly found mildly elevated bacterial burden in spleen and liver of IL-17A-/- mice as compared with WT mice. Overall, IL-17A-/- mice showed reduced clearance of S. Enteritidis. S. Enteritidis-specific IL-17A production was induced in splenocytes and lymph node cells of infected WT mice at both time points, 20 and 80 d.p.i. Classical CD4+ T(h)17 cells developed upon infection with Salmonella. CD4- gammadelta TCR+ and CD4- gammadelta TCR- cells were found to be additional IL-17A-producing cell populations. In infected IL-17A-/- mice, a normal T(h)1 cytokine profile was observed consistent with the overall subtle phenotype. Nevertheless, in the absence of IL-17A, recruitment of neutrophils and delayed-type hypersensitivity (DTH) reactivity was significantly compromised. Our data indicate that IL-17A responses are induced by Salmonella and mildly contribute to protective immunity during S. Enteritidis infection. Thus, IL-17A complements the IL-12/IFN-gamma axis which is essential for protective immunity against salmonellosis in mice and men.

Analysis of cells targeted by Salmonella type III secretion in vivo

The type III secretion systems (TTSS) encoded in Salmonella pathogenicity island-1 and -2 (SPI-1 and -2) are virulence factors required for specific phases of Salmonella infection in animal hosts. However, the host cell types targeted by the TTSS have not been determined. To investigate this, we have constructed translational fusions between the ß-lactamase reporter and a broad array of TTSS effectors secreted via SPI-1, SPI-2, or both. Secretion of the fusion protein to a host cell was determined by cleavage of a specific fluorescent substrate. In cultured cells, secretion of all six effectors could be observed. However, two to four days following i.p. infection of mice, only effectors secreted by SPI-2 were detected in spleen cells. The cells targeted were identified via staining with nine different cell surface markers followed by FACS analysis as well as by conventional cytological methods. The targeted cells include B and T lymphocytes, neutrophils, monocytes, and dendritic cells, but not mature macrophages. To further investigate replication in these various cell types, Salmonella derivatives were constructed that express a red fluorescent protein. Bacteria could be seen in each of the cell types above; however, most viable bacteria were present in neutrophils. We find that Salmonella is capable of targeting most phagocytic and non-phagocytic cells in the spleen but has a surprisingly high preference for neutrophils. These findings suggest that Salmonella specifically target splenic neutrophils presumably to attenuate their microbicidal functions, thereby promoting intracellular survival and replication in the mouse.

Bacteria of the Salmonella genus are important human pathogens and a leading cause of food-borne illness. Salmonella species' ability to cause disease relies on the activities of two sophisticated molecular syringes that allow the bacteria to pump proteins into cells that they infect. The activities of these syringes have been studied extensively in cells grown under laboratory conditions and shown to be essential for the infectious process in animal models. However, the specific cells within infected organs that are targeted by these syringes have not been identified. In this work we describe the specific spleen cells targeted by Salmonella in the mouse. We find that Salmonella is capable of targeting most cell types using their molecular syringes. Quite surprisingly, we find that Salmonella mostly targets neutrophils, a cell type not thought to be associated with live Salmonella in host tissues. These findings challenge our current views of Salmonella infection and may lead to new insight for treating the disease.

Analysis of nitric oxide-dependent antimicrobial actions in macrophages and mice

Nitric oxide (NO*) is a critical component of mammalian host defense that is produced in macrophages and other cells comprising the innate immune system. Isolated mammalian macrophages have been utilized to measure the kinetics of NO production and to demonstrate NO-related antimicrobial actions. Some microorganisms possess enzymes to detoxify nitrogen oxides, and mutant strains lacking these enzymes can be used to demonstrate the importance of these mechanisms for intracellular bacterial survival. This chapter describes techniques with which to analyze the antimicrobial actions of nitric oxide in murine and human macrophages and in laboratory mice.