Surface charge and hydrophobicity of Campylobacter jejuni strains in relation to adhesion to epithelial HT-29 cells

Campylobacter jejuni Virulence Factors Identified by Modulating Their Synthesis on Ribosomes With Altered rRNA Methylation

Campylobacter jejuni is a major cause of food poisoning worldwide, and remains the main infective agent in gastroenteritis and related intestinal disorders in Europe and the USA. As with all bacterial infections, the stages of adhesion to host tissue, survival in the host and eliciting disease all require the synthesis of proteinaceous virulence factors on the ribosomes of the pathogen. Here, we describe how C. jejuni virulence is attenuated by altering the methylation of its ribosomes to disrupt the composition of its proteome, and how this in turn provides a means of identifying factors that are essential for infection and pathogenesis. Specifically, inactivation of the C. jejuni Cj0588/TlyA methyltransferase prevents methylation of nucleotide C1920 in the 23S rRNA of its ribosomes and reduces the pathogen’s ability to form biofilms, to attach, invade and survive in host cells, and to provoke the innate immune response. Mass spectrometric analyses of C. jejuni TlyA-minus strains revealed an array of subtle changes in the proteome composition. These included reduced amounts of the cytolethal distending toxin (CdtC) and the MlaEFD proteins connected with outer membrane vesicle (OMV) production. Inactivation of the cdtC and mlaEFD genes confirmed the importance of their encoded proteins in establishing infection. Collectively, the data identify a subset of genes required for the onset of human campylobacteriosis, and serve as a proof of principle for use of this approach in detecting proteins involved in bacterial pathogenesis.

Universal Enzyme-Based Field Workflow for Rapid and Sensitive Quantification of Water Pathogens

A universal filtration and enzyme-based workflow has been established to allow for the rapid and sensitive quantification of leading pathogens Cryptosporidium parvum, Giardia gamblia, Campylobacter jejuni, and Escherichia coli from tap water samples with volumes up to 100 mL, and the potential to scale up to larger volumes. qPCR limits of quantification as low as four oocysts for Cryptosporidium, twelve cysts for Giardia, two cells for C. jejuni, and nineteen cells for E. coli per reaction were achieved. A polycarbonate filter-based sampling method coupled with the prepGEM enzyme-based DNA extraction system created a single-step transfer workflow that required as little as 20 min of incubation time and a 100 µL reaction mix. The quantification via qPCR was performed directly on the prepGEM extract, bypassing time-consuming, labour-intensive conventional culture-based methods. The tap water samples were shown to contain insoluble particles that inhibited detection by reducing the quantification efficiency of a representative pathogen (C. jejuni) to 30-60%. This sample inhibition was effectively removed by an on-filter treatment of 20% (v/v) phosphoric acid wash. Overall, the established workflow was able to achieve quantification efficiencies of 92% and higher for all four leading water pathogens, forming the basis of a rapid, portable, and low-cost solution to water monitoring.

Role of capsular polysaccharides and lipooligosaccharides in Campylobacter surface properties, autoagglutination, and attachment to abiotic surfaces

The role of capsular polysaccharides and lipooligosaccharides in cell surface hydrophobicity, surface charge, autoagglutination (AAG), and attachment to abiotic surfaces of three strains of Campylobacter jejuni and one strain of C. coli were investigated. This was achieved by removal of capsular polysaccharides and truncation of lipooligosaccharides core oligosaccharides by inactivation of the kpsE and waaF genes, respectively. The mutants and the wild-type strains were compared after growth under planktonic (broth) and sessile (agar) conditions. Cells grown as planktonic cultures showed a significantly (p<0.05) higher degree of hydrophobicity and AAG activity but differed from their sessile counterparts with respect to surface charge and attachment counts, depending on the strain. These results suggest that prior mode of growth affects the surface properties and attachment of Campylobacter in a strain-dependent manner. There were no significant (p>0.05) differences between the three C. jejuni strains and their ΔkpsE and ΔwaaF mutants with respect to all traits tested. Inactivation of the kpsE gene significantly (p<0.05) reduced the surface charge of the C. coli strain from ∼-10 to ∼-6 mV and increased its AAG activity, while disruption of the waaF gene significantly (p<0.05) increased its surface hydrophobicity by >8° and decreased the numbers of cells attaching to stainless steel and glass by ∼0.5 log/cm². These results suggest that surface polysaccharides may influence the surface properties and attachment to abiotic surfaces of C. coli but not C. jejuni. This suggestion, however, requires further investigation using a larger number of strains of both species.

Effects of Bacillus anthracis hydrophobicity and induction of host cell death on sample collection from environmental surfaces

The objective of this study is to determine whether DNA signature recovery of Bacillus anthracis strains from different environmental substrates correlates with pathogen cell surface hydrophobicity and induction of host cell death. We compared recovery of DNA signatures from a panel of B. anthracis strains collected from two environmental substrates, non-porous surfaces and soil, using real-time qPCR. We further assessed both cell surface hydrophobicity of the B. anthracis strains by contact angle measurements and host cell viability in response to B. anthracis infection in a mouse macrophage cell model system. Our studies demonstrated correlation between reduced B. anthracis sample recovery from environmental substrates and increased cell surface hydrophobicity. Surprisingly, the most hydrophilic strain, K4596, which exhibited the highest level of recovery from the environmental surfaces, induced the highest level of host cell cytotoxicity compared to more hydrophobic B. anthracis strains in the panel. Our results suggest that cell surface hydrophobicity may play a leading role in mediating pathogen adherence to environmental surfaces. These findings can contribute to the optimization of pathogen detection efforts by understanding how bacterial parameters such as hydrophobicity and induction of host cell death affect bacterial adherence to environmental surfaces.

Weaning pig performance and faecal microbiota with and without in-feed addition of rare earth elements

Two 6-week feeding trials were conducted on a total of 112 newly weaned piglets to examine the recently reported growth promoting effects of dietary rare earth elements (REE) in European pig production. Rare earth element-diets were supplemented with a REE-citrate premix of lanthanum and the light lanthanoides cerium, praseodymium and neodymium at 200 mg/kg for 6 weeks after weaning. Overall for both trials, growth performance of REE-citrate and control fed piglets did not differ significantly (p > 0.05). An early enhancive tendency for REE-citrate in trial 1 (feed conversion ratio, FCR -3%, p = 0.15) proved irreproducible in trial 2. In the late period of trial 1, in-feed addition of REE-citrate significantly impaired piglet performance (FCR + 8%, p = 0.01). A cultivation-independent molecular approach, polymerase chain reaction-denaturing gradient gel electrophoresis was further applied to assess REE induced alterations in the predominant faecal microbiota from weaning pigs. Calculation of various ecological characteristics does not indicate (p > 0.05) an often discussed selective effect on local microbial composition of dietary REE.

Comparison of Escherichia coli and Campylobacter jejuni transport in saturated porous media

Due to the difficulties in testing for specific pathogens, water samples are tested for the presence of nonpathogenic indicator organisms to determine whether a water supply has been contaminated by fecal material. An implicit assumption in this approach is that where pathogenic microorganisms are present fecal indicator organisms are present as well; yet surprisingly few studies have been conducted that directly compare the transport of indicator organisms with pathogenic organisms in ground water environments. In this study we compared the cell properties and transport of Escherichia coli, a commonly used indicator organism, and Campylobacter jejuni, an important enteropathogen commonly found in agricultural wastes, through saturated porous media. Differences in cell properties were determined by measuring cell geometry, hydrophobicity, and electrophoretic mobility. Transport differences were determined by conducting miscible displacement experiments in laboratory columns. Under the experimental conditions tested, C. jejuni was much more negatively charged and more hydrophobic than E. coli. In addition, C. jejuni cells were slightly longer, narrower, and less spherical than E. coli. The variations in cell properties, primarily surface charge, resulted in significant differences in transport between these two microorganisms, with the transport of C. jejuni exceeding that of E. coli when conditions favored low attachment rates, thus calling into question the usefulness of using E. coli as an indicator organism for this important pathogen.

Enhancing transport of hydrogenophaga flava ENV735 for bioaugmentation of aquifers contaminated with methyl tert-butyl ether

The gasoline oxygenate methyl tert-butyl ether (MTBE) has become a widespread contaminant in groundwater throughout the United States. Bioaugmentation of aquifers with MTBE-degrading cultures may be necessary to enhance degradation of the oxygenate in some locations. However, poor cell transport has sometimes limited bioaugmentation efforts in the past. The objective of this study was to evaluate the transport characteristics of Hydrogenophaga flava ENV735, a pure culture capable of growth on MTBE, and to improve movement of the strain through aquifer solids. The wild-type culture moved only a few centimeters in columns of aquifer sediment. An adhesion-deficient variant (H. flava ENV735:24) of the wild-type strain that moved more readily through sediments was obtained by sequential passage of cells through columns of sterile sediment. Hydrophobic and electrostatic interaction chromatography revealed that the wild-type strain is much more hydrophobic than the adhesion-deficient variant. Electrophoretic mobility assays and transmission electron microscopy showed that the wild-type bacterium contains two distinct subpopulations, whereas the adhesion-deficient strain has only a single, homogeneous population. Both the wild-type strain and adhesion-deficient variant degraded MTBE, and both were identified by 16S rRNA analysis as pure cultures of H. flava. The effectiveness of surfactants for enhancing transport of the wild-type strain was also evaluated. Many of the surfactants tested were toxic to ENV735; however, one nonionic surfactant, Tween 20, enhanced cell transport in sand columns. Improving microbial transport may lead to a more effective bioaugmentation strategy for MTBE-contaminated sites where indigenous oxygenate degraders are absent.

Contribution of the hydrophobic effect to microbial infection

The hydrophobic effect has been known for decades. Numerous researchers have invoked the hydrophobic effect to explain how pathogens adhere to tissues. In some cases, inhibition of adhesion can be brought about by low concentrations of aromatic compounds, such as p-nitrophenol or tryptophan. Because the hydrophobic effect has been considered to be nonspecific, the molecular biology of adhesive hydrophobins has not been studied in as much detail as lectin adhesins. The literature provides compelling evidence that a large number of bacterial and fungal pathogens depend on hydrophobic interactions for successful colonization of a host. Several laboratories are now developing effective antiadhesins, based on inhibition of hydrophobic interactions between the host and the pathogen.

Interactions between Campylobacter jejuni and lipids

We previously showed that motility plays several key roles in Campylobacter jejuni pathogenesis, including increasing the efficiency of C. jejuni attachment to host epithelial cells. To further characterize C. jejuni attachment, we first examined the role of carbohydrates. Experiments with Chinese hamster ovary (CHO) cell mutants with defined defects in complex carbohydrate biosynthesis revealed that oligosaccharide sequences probably play a subordinate role in C. jejuni attachment to eukaryotic cells. Simple sugars such as mannose, fucose, glucose, N-acetylglucosamine, maltose, and galactose also did not significantly alter the binding of C. jejuni to CHO cells. Thin-layer chromatography overlay analysis with lipids extracted from CHO cells suggested that C. jejuni binds to lipids. Lipid binding was further investigated using a receptor-based enzyme-linked immunosorbent assay. Hydrophobic interactions were determined to play a minor role in binding, since tetramethylurea, a strong inhibitor of hydrophobic interactions, did not significantly decrease binding between C. jejuni and lipids. The interaction was dissected further by comparing the binding of C. jejuni to lipids and their derivatives. The results showed that binding was greatest to the entire lipid structure and decreased in affinity when portions of the lipid were removed. Thin-layer chromatography overlay analysis showed that lipids with unsaturated fatty acids were bound with the highest affinity. Our results suggest that C. jejuni may interact with lipids in host cell membranes. However, lipids only partially inhibited C. jejuni binding to CHO cells, suggesting that multiple interactions occur between the bacteria and host cells.

The influence of A-band and B-band lipopolysaccharide on the surface characteristics and adhesion of Pseudomonas aeruginosa to surfaces

Pseudomonas aeruginosa PAO1 possesses two distinct lipopolysaccharide (LPS) O-polysaccharide species, A- and B-band LPS, the relative expression of which appears to be under environmental control. In an attempt to identify the influence these LPS types have on surface characteristics and adhesion, we examined the surface hydrophobicity and surface charge of P. aeruginosa PAO1 (O5 serotype) and its isogenic LPS derivatives which possessed A+B-, A-B+ and A-B- LPS. The surface characteristics of the strains affected their ability to adhere to hydrophilic (glass) and hydrophobic (polystyrene) surfaces. Cells possessing only A-band LPS demonstrated the highest surface hydrophobicity, followed by the strain lacking both A- and B-band LPS. The presence of B-band LPS resulted in a more hydrophilic surface. Strains lacking B-band LPS (A+B- and A-B-) had more electronegative surfaces than those possessing B-band LPS (A+B+ and A-B+), with cells lacking both A- and B-band LPS showing the highest surface electronegativity. These data suggest that the main surface-charge-determining groups reside in the core region of the LPS molecule. Cells with the lowest surface hydrophobicity and lowest surface charge (A+B+, A-B+) adhered to glass the most efficiently, implying a role for electrostatic interaction, whereas adhesion to polystyrene mirrored the relative hydrophobicities of the strains (A+B- > A-B- > A+B+ > A-B+). It is postulated that phenotypic variation in the relative expression of A- and B-band LPS may be a mechanism by which P. aeruginosa can alter its overall surface characteristics in such a way as to influence adhesion and favour survival.

In vitro surface properties of the newly recognized gastric pathogen Helicobacter pylori

There appears to be a particular association between Helicobacter pylori and the gastric antrum, but the mechanisms by which the organism adheres to and colonizes the gastric mucosa are unclear. Surface hydrophobicity and surface charge mediate the adherence of other bacterial pathogens to mucosal epithelial cell surfaces. Therefore, in this study we characterized both the surface hydrophobicity and the surface charge of 10 H. pylori strains grown in broth culture. Four complementary methods were used to determine hydrophobicity: hydrophobic interaction chromatography, the salt aggregation test, comparison of bacterial adherence to polystyrene with adherence to sulfonated polystyrene, and measurement of contact angle with droplets of water. Three of the methods (salt aggregation test, adherence to polystyrene, and contact angles) indicated that each of the 10 strains expressed a relatively hydrophilic cell surface. In contrast, hydrophobic interaction chromatography determinations with both phenyl- and octyl-Sepharose suggested that the H. pylori strains were relatively hydrophobic. However, tetramethyl urea (0.4 M) did not reduce the binding of H. pylori to phenyl-Sepharose columns. DEAE-cellulose ion-exchange chromatography showed that each of the 10 strains of H. pylori had a surface which, overall, was highly negatively charged. We conclude that H. pylori expresses an overall relatively hydrophilic and negatively charged surface in vitro.

Interaction of Campylobacter jejuni with extracellular matrix components

The adhesion of three strains of Campylobacter jejuni to coverslips and microwells coated with isolated extracellular matrix components, fibronectin, laminin and types I, III, IV and V collagens was studied. Fibronectin mediated the adherence of C. jejuni, but there were differences in the binding capacities of the strains. Type I, III and V collagens mediated very strongly the attachment of two strains of C. jejuni. All three strains attached weakly to basement membrane-specific type IV collagen. Laminin was capable of mediating the adhesion only when present at a higher concentration. The observations indicate that extracellular matrix components may serve as anchor molecules for C. jejuni adhesion and that several attachment mechanisms occur simultaneously.