JlpA, a novel surface-exposed lipoprotein specific to Campylobacter jejuni, mediates adherence to host epithelial cells

Gene expression profile of Campylobacter jejuni in response to macrolide antibiotics

Campylobacter jejuni is a foodborne pathogen that causes gastroenteritis in humans and has developed resistance to various antibiotics. The primary objective of this research was to examine the network of antibiotic resistance in C. jejuni. The study involved the wild and antibiotic-resistant strains placed in the presence and absence of antibiotics to review their gene expression profiles in response to ciprofloxacin via microarray. Differentially expressed genes (DEGs) analysis and Protein-Protein Interaction (PPI) Network studies were performed for these genes. The results showed that the resistance network of C. jejuni is modular, with different genes involved in bacterial motility, capsule synthesis, efflux, and amino acid and sugar synthesis. Antibiotic treatment resulted in the down-regulation of cluster genes related to translation, flagellum formation, and chemotaxis. In contrast, cluster genes involved in homeostasis, capsule formation, and cation efflux were up-regulated. The study also found that macrolide antibiotics inhibit the progression of C. jejuni infection by inactivating topoisomerase enzymes and increasing the activity of epimerase enzymes, trying to compensate for the effect of DNA twisting. Then, the bacterium limits the movement to conserve energy. Identifying the antibiotic resistance network in C. jejuni can aid in developing drugs to combat these bacteria. Genes involved in cell division, capsule formation, and substance transport may be potential targets for inhibitory drugs. Future research must be directed toward comprehending the underlying mechanisms contributing to the modularity of antibiotic resistance and developing strategies to disrupt and mitigate the growing threat of antibiotic resistance effectively.

High molecular/low acetylated chitosans reduce adhesion of Campylobacter jejuni to host cells by blocking JlpA

Infections caused by Campylobacter spp. are a major cause of severe enteritis worldwide. Multifactorial prevention strategies are necessary to reduce the prevalence of Campylobacter. In particular, antiadhesive strategies with specific inhibitors of early host-pathogen interaction are promising approaches to reduce the bacterial load. An in vitro flow cytometric adhesion assay was established to study the influence of carbohydrates on the adhesion of C. jejuni to Caco-2 cells. Chitosans with a high degree of polymerization and low degree of acetylation were identified as potent antiadhesive compounds, exerting significant reduction of C. jejuni adhesion to Caco-2 cells at non-toxic concentrations. Antiadhesive and also anti-invasive effects were verified by confocal laser scanning microscopy. For target identification, C. jejuni adhesins FlpA and JlpA were expressed in Escherichia coli ArcticExpress, and the influence of chitosan on binding to fibronectin and HSP90α, respectively, was investigated. While no effects on FlpA binding were found, a strong inhibition of JlpA-HSP90α binding was observed. To simulate real-life conditions, chicken meat was inoculated with C. jejuni, treated with antiadhesive chitosan, and the bacterial load was quantified. A strong reduction of C. jejuni load was observed. Atomic force microscopy revealed morphological changes of C. jejuni after 2 h of chitosan treatment, indicating disturbance of the cell wall and sacculi formation by electrostatic interaction of positively charged chitosan with the negatively charged cell surface. In conclusion, our data indicate promising antiadhesive and anti-invasive potential of high molecular weight, strongly de-acetylated chitosans for reducing C. jejuni load in livestock and food production. KEY POINTS: • Antiadhesive effects of chitosan with high DP/low DA against C. jejuni to host cells • Specific targeting of JlpA/Hsp90α interaction by chitosan • Meat treatment with chitosan reduces C. jejuni load.

Campylobacter jejuni: targeting host cells, adhesion, invasion, and survival

Campylobacter jejuni, causing strong enteritis, is an unusual bacterium with numerous peculiarities. Chemotactically controlled motility in viscous milieu allows targeted navigation to intestinal mucus and colonization. By phase variation, quorum sensing, extensive O-and N-glycosylation and use of the flagellum as type-3-secretion system C. jejuni adapts effectively to environmental conditions. C. jejuni utilizes proteases to open cell-cell junctions and subsequently transmigrates paracellularly. Fibronectin at the basolateral side of polarized epithelial cells serves as binding site for adhesins CadF and FlpA, leading to intracellular signaling, which again triggers membrane ruffling and reduced host cell migration by focal adhesion. Cell contacts of C. jejuni results in its secretion of invasion antigens, which induce membrane ruffling by paxillin-independent pathway. In addition to fibronectin-binding proteins, other adhesins with other target structures and lectins and their corresponding sugar structures are involved in host-pathogen interaction. Invasion into the intestinal epithelial cell depends on host cell structures. Fibronectin, clathrin, and dynein influence cytoskeletal restructuring, endocytosis, and vesicular transport, through different mechanisms. C. jejuni can persist over a 72-h period in the cell. Campylobacter-containing vacuoles, avoid fusion with lysosomes and enter the perinuclear space via dynein, inducing signaling pathways. Secretion of cytolethal distending toxin directs the cell into programmed cell death, including the pyroptotic release of proinflammatory substances from the destroyed cell compartments. The immune system reacts with an inflammatory cascade by participation of numerous immune cells. The development of autoantibodies, directed not only against lipooligosaccharides, but also against endogenous gangliosides, triggers autoimmune diseases. Lesions of the epithelium result in loss of electrolytes, water, and blood, leading to diarrhea, which flushes out mucus containing C. jejuni. Together with the response of the immune system, this limits infection time. Based on the structural interactions between host cell and bacterium, the numerous virulence mechanisms, signaling, and effects that characterize the infection process of C. jejuni, a wide variety of targets for attenuation of the pathogen can be characterized. The review summarizes strategies of C. jejuni for host-pathogen interaction and should stimulate innovative research towards improved definition of targets for future drug development. KEY POINTS: • Bacterial adhesion of Campylobacter to host cells and invasion into host cells are strictly coordinated processes, which can serve as targets to prevent infection. • Reaction and signalling of host cell depend on the cell type. • Campylobacter virulence factors can be used as targets for development of antivirulence drug compounds.

The Missing Pieces: The Role of Secretion Systems in Campylobacter jejuni Virulence

Campylobacter jejuni is likely the most common bacterial cause of gastroenteritis worldwide, responsible for millions of cases of inflammatory diarrhea characterized by severe abdominal cramps and blood in the stool. Further, C. jejuni infections are associated with post-infection sequelae in developed countries and malnutrition and growth-stunting in low- and middle-income countries. Despite the increasing prevalence of the disease, campylobacteriosis, and the recognition that this pathogen is a serious health threat, our understanding of C. jejuni pathogenesis remains incomplete. In this review, we focus on the Campylobacter secretion systems proposed to contribute to host-cell interactions and survival in the host. Moreover, we have applied a genomics approach to defining the structural and mechanistic features of C. jejuni type III, IV, and VI secretion systems. Special attention is focused on the flagellar type III secretion system and the prediction of putative effectors, given that the proteins exported via this system are essential for host cell invasion and the inflammatory response. We conclude that C. jejuni does not possess a type IV secretion system and relies on the type III and type VI secretion systems to establish a niche and potentiate disease.

Effective Platform for the Production of Recombinant Outer Membrane Vesicles in Gram-Negative Bacteria

Bacterial outer membrane vesicles (OMVs) typically contain multiple immunogenic molecules that include antigenic proteins, making them good candidates for vaccine development. In animal models, vaccination with OMVs has been shown to confer protective immune responses against many bacterial diseases. It is possible to genetically introduce heterologous protein antigens to the bacterial host that can then be produced and relocated to reside within the OMVs by means of the host secretion mechanisms. Accordingly, in this study we sought to develop a novel platform for recombinant OMV (rOMV) production in the widely used bacterial expression host species, Escherichia coli. Three different lipoprotein signal peptides including their Lol signals and tether sequences-from Neisseria meningitidis fHbp, Leptospira interrogans LipL32, and Campylobactor jejuni JlpA-were combined upstream to the GFPmut2 model protein, resulting in three recombinant plasmids. Pilot expression studies showed that the fusion between fHbp and GFPmut2 was the only promising construct; therefore, we used this construct for large-scale expression. After inducing recombinant protein expression, the nanovesicles were harvested from cell-free culture media by ultrafiltration and ultracentrifugation. Transmission electron microscopy demonstrated that the obtained rOMVs were closed, circular single-membrane particles, 20-200 nm in size. Western blotting confirmed the presence of GFPmut2 in the isolated vesicles. Collectively, although this is a non-optimized, proof-of-concept study, it demonstrates the feasibility of this platform in directing target proteins into the vesicles for OMV-based vaccine development.

Agents of Campylobacteriosis in Different Meat Matrices in Brazil

We aimed to identify the prevalence of thermophilic species of Campylobacter in meats of different species available on the Brazilian commercial market and to determine the genetic diversity, antimicrobial resistance and virulence potential of the isolates. A total of 906 samples, including chicken, beef and pork carcasses and chicken and beef livers, were purchased in retail outlets, and prevalences of 18.7% (46/246), 3.62% (5/138), 10.14% (14/138), 3.62% (5/138) and 4.47% (11/132), respectively, were identified, evidencing the dissemination of genotypes in the main producing macro-regions. Of all isolates, 62.8% were classified as multidrug resistant (MDR), with resistance to amoxicillin-clavulanate (49.4%), tetracycline (51.8%) and ciprofloxacin (50.6%) and co-resistance to macrolides and fluoroquinolones (37.1%). Multivirulent profiles were identified mainly in isolates from chicken carcasses (84.8%), and the emergence of MDR/virulent strains was determined in pork isolates. All isolates except those from chicken carcasses showed a high potential for biofilm formation (71.4% luxS) and consequent persistence in industrial food processing. For chicken carcasses, the general virulence was higher in C. jejuni (54.3%), followed by C. coli (24%) and Campylobacter spp. (21.7%), and in the other meat matrices, Campylobacter spp. showed a higher prevalence of virulence (57.2%). The high rates of resistance and virulence reinforce the existence of strain selection pressure in the country, in addition to the potential risk of strains isolated not only from chicken carcasses, but also from other meat matrices.

A Putative Lipoprotein Mediates Cell-Cell Contact for Type VI Secretion System-Dependent Killing of Specific Competitors

Interbacterial competition is prevalent in host-associated microbiota, where it can shape community structure and function, impacting host health in both positive and negative ways. However, the factors that permit bacteria to discriminate among their various neighbors for targeted elimination of competitors remain elusive. We identified a putative lipoprotein (TasL) in Vibrio species that mediates cell-cell attachment with a subset of target strains, allowing inhibitors to target specific competitors for elimination. Here, we describe this putative lipoprotein, which is associated with the broadly distributed type VI secretion system (T6SS), by studying symbiotic Vibrio fischeri, which uses the T6SS to compete for colonization sites in their squid host. We demonstrate that TasL allows V. fischeri cells to restrict T6SS-dependent killing to certain genotypes by selectively integrating competitor cells into aggregates while excluding other cell types. TasL is also required for T6SS-dependent competition within juvenile squid, indicating that the adhesion factor is active in the host. Because TasL homologs are found in other host-associated bacterial species, this newly described cell-cell attachment mechanism has the potential to impact microbiome structure within diverse hosts. IMPORTANCE T6SSs are broadly distributed interbacterial weapons that share an evolutionary history with bacteriophage. Because the T6SS can be used to kill neighboring cells, it can impact the spatial distribution and biological function of both free-living and host-associated microbial communities. Like their phage relatives, T6SS⁺ cells must sufficiently bind competitor cells to deliver their toxic effector proteins through the syringe-like apparatus. Although phage use receptor-binding proteins (RBPs) and tail fibers to selectively bind prey cells, the biophysical properties that mediate this cell-cell contact for T6SS-mediated killing remain unknown. Here, we identified a large, predicted lipoprotein that is coordinately expressed with T6SS proteins and facilitates the contact that is necessary for the T6SS-dependent elimination of competitors in a natural host. Similar to phage RBPs and tail fibers, this lipoprotein is required for T6SS⁺ cells to discriminate between prey and nonprey cell types, revealing new insight into prey selection during T6SS-mediated competition.

Exploiting pglB Oligosaccharyltransferase-Positive and -Negative Campylobacter jejuni and a Multiprotease Digestion Strategy to Identify Novel Sites Modified by N-Linked Protein Glycosylation

Campylobacter jejuni is a bacterial pathogen encoding a unique N-linked glycosylation (pgl) system that mediates attachment of a heptasaccharide to N-sequon-containing membrane proteins by the PglB oligosaccharyltransferase (OST). Many targets of PglB are known, yet only a fraction of sequons are experimentally confirmed, and site occupancy remains elusive. We exploited pglB-positive (wild-type; WT) and -negative (ΔpglB) proteomes to identify potential glycosites. The nonglycosylated forms of known glycopeptides were typically increased in protein normalized abundance in ΔpglB relative to WT and restored by pglB reintroduction (ΔpglB::pglB). Sequon-containing peptide abundances were thus consistent with significant site occupancy in the presence of the OST. Peptides with novel sequons were either unaltered (likely not glycosylated) or showed abundance consistent with known glycopeptides. Topology analysis revealed that unaltered sequons often displayed cytoplasmic localization, despite originating from membrane proteins. Novel glycosites were confirmed using parallel multiprotease digestion, LC-MS/MS, and FAIMS-MS to define the glycoproteomes of WT and ΔpglB::pglB C. jejuni. We identified 142 glycosites, of which 32 were novel, and 83% of sites predicted by proteomics were validated. There are now 166 experimentally verified C. jejuni glycosites and evidence for occupancy or nonoccupancy of 31 additional sites. This study serves as a model for the use of OST-negative cells and proteomics for highlighting novel glycosites and determining occupancy in a range of organisms.

Virulence factors of foodborne pathogen Campylobacterjejuni

Campylobacter jejuni is a highly frequent cause of gastrointestinal foodborne disease in humans throughout the world. Disease outcomes vary from mild to severe diarrhea, and in rare cases the Guillain-Barré syndrome or reactive arthritis can develop as a post-infection complication. Transmission to humans usually occurs via the consumption of a range of foods, especially those associated with the consumption of raw or undercooked poultry meat, unpasteurized milk, and water-based environmental sources. When associated to food or water ingestion, the C. jejuni enters the human host intestine via the oral route and colonizes the distal ileum and colon. When it adheres and colonizes the intestinal cell surfaces, the C. jejuni is expected to express several putative virulence factors, which cause damage to the intestine either directly, by cell invasion and/or production of toxin(s), or indirectly, by triggering inflammatory responses. This review article highlights various C. jejuni characteristics - such as motility and chemotaxis - that contribute to the biological fitness of the pathogen, as well as factors involved in human host cell adhesion and invasion, and their potential role in the development of the disease. We have analyzed and critically discussed nearly 180 scientific articles covering the latest improvements in the field.

Multi-Omics Approach Reveals the Potential Core Vaccine Targets for the Emerging Foodborne Pathogen Campylobacter jejuni

Campylobacter jejuni is a leading cause of bacterial gastroenteritis in humans around the world. The emergence of bacterial resistance is becoming more serious; therefore, development of new vaccines is considered to be an alternative strategy against drug-resistant pathogen. In this study, we investigated the pangenome of 173 C. jejuni strains and analyzed the phylogenesis and the virulence factor genes. In order to acquire a high-quality pangenome, genomic relatedness was firstly performed with average nucleotide identity (ANI) analyses, and an open pangenome of 8,041 gene families was obtained with the correct taxonomy genomes. Subsequently, the virulence property of the core genome was analyzed and 145 core virulence factor (VF) genes were obtained. Upon functional genomics and immunological analyses, five core VF proteins with high antigenicity were selected as potential core vaccine targets for humans. Furthermore, functional annotations indicated that these proteins are involved in important molecular functions and biological processes, such as adhesion, regulation, and secretion. In addition, transcriptome analysis in human cells and pig intestinal loop proved that these vaccine target genes are important in the virulence of C. jejuni in different hosts. Comprehensive pangenome and relevant animal experiments will facilitate discovering the potential core vaccine targets with improved efficiency in reverse vaccinology. Likewise, this study provided some insights into the genetic polymorphism and phylogeny of C. jejuni and discovered potential vaccine candidates for humans. Prospective development of new vaccines using the targets will be an alternative to the use of antibiotics and prevent the development of multidrug-resistant C. jejuni in humans and even other animals.

Identifying the targets and functions of N-linked protein glycosylation in Campylobacter jejuni

Campylobacter jejuni is a major cause of bacterial gastroenteritis in humans that is primarily associated with the consumption of inadequately prepared poultry products, since the organism is generally thought to be asymptomatic in avian species. Unlike many other microorganisms, C. jejuni is capable of performing extensive post-translational modification (PTM) of proteins by N- and O-linked glycosylation, both of which are required for optimal chicken colonization and human virulence. The biosynthesis and attachment of N-glycans to C. jejuni proteins is encoded by the pgl (protein glycosylation) locus, with the PglB oligosaccharyltransferase (OST) enabling en bloc transfer of a heptasaccharide N-glycan from a lipid carrier in the inner membrane to proteins exposed within the periplasm. Seventy-eight C. jejuni glycoproteins (represented by 134 sites of experimentally verified N-glycosylation) have now been identified, and include inner and outer membrane proteins, periplasmic proteins and lipoproteins, which are generally of poorly defined or unknown function. Despite our extensive knowledge of the targets of this apparently widespread process, we still do not fully understand the role N-glycosylation plays biologically, although several phenotypes, including wild-type stress resistance, biofilm formation, motility and chemotaxis have been related to a functional pgl system. Recent work has described enzymatic processes (nitrate reductase NapAB) and antibiotic efflux (CmeABC) as major targets requiring N-glycan attachment for optimal function, and experimental evidence also points to roles in cell binding via glycan-glycan interactions, protein complex formation and protein stability by conferring protection against host and bacterial proteolytic activity. Here we examine the biochemistry of the N-linked glycosylation system, define its currently known protein targets and discuss evidence for the structural and functional roles of this PTM in individual proteins and globally in C. jejuni pathogenesis.

Campylobacter Virulence Factors and Molecular Host-Pathogen Interactions

Campylobacter jejuni and Campylobacter coli can be frequently isolated from poultry and poultry-derived products, and in combination these two species cause a large portion of human bacterial gastroenteritis cases. While birds are typically colonized by these Campylobacter species without clinical symptoms, in humans they cause (foodborne) infections at high frequencies, estimated to cost billions of dollars worldwide every year. The clinical outcome of Campylobacter infections comprises malaise, diarrhea, abdominal pain and fever. Symptoms may continue for up to two weeks and are generally self-limiting, though occasionally the disease can be more severe or result in post-infection sequelae. The virulence properties of these pathogens have been best-characterized for C. jejuni, and their actions are reviewed here. Various virulence-associated bacterial determinants include the flagellum, numerous flagellar secreted factors, protein adhesins, cytolethal distending toxin (CDT), lipooligosaccharide (LOS), serine protease HtrA and others. These factors are involved in several pathogenicity-linked properties that can be divided into bacterial chemotaxis, motility, attachment, invasion, survival, cellular transmigration and spread to deeper tissue. All of these steps require intimate interactions between bacteria and host cells (including immune cells), enabled by the collection of bacterial and host factors that have already been identified. The assortment of pathogenicity-associated factors now recognized for C. jejuni, their function and the proposed host cell factors that are involved in crucial steps leading to disease are discussed in detail.

A Systematic Review of Campylobacter jejuni Vaccine Candidates for Chickens

Campylobacter jejuni infection linked to the consumption of contaminated poultry products is one of the leading causes of human enteric illness worldwide. Vaccination of chickens is one of the potential strategies that could be used to control C. jejuni colonization. To date, various C. jejuni vaccines using potential antigens have been evaluated, but a challenge in identifying the most effective formulation is the wide variability in vaccine efficacies reported. A systematic review was undertaken to compare C. jejuni vaccine studies. Based upon specific selection criteria eligible papers were identified and included in the analysis. Vaccine efficacy reported from different C. jejuni antigens, vaccine types, and vaccination regimens reported in these papers were reviewed. Our analysis shows that total outer membrane proteins and cysteine ABC transporter substrate-binding protein were among the most efficacious vaccine antigen candidates reported. This review also highlights the importance of the need for increased consistency in the way C. jejuni vaccine studies in poultry are designed and reported in order to be able to undertake a robust comparison of C. jejuni vaccine candidates.

Vaccines against gastroenteritis, current progress and challenges

Enteric viral and bacterial infections continue to be a leading cause of mortality and morbidity in young children in low-income and middle-income countries, the elderly, and immunocompromised individuals. Vaccines are considered an effective and practical preventive approach against the predominantly fecal-to-oral transmitted gastroenteritis particularly in the resource-limited countries or regions where implementation of sanitation systems and supply of safe drinking water are not quickly achievable. While vaccines are available for a few enteric pathogens including rotavirus and cholera, there are no vaccines licensed for many other enteric viral and bacterial pathogens. Challenges in enteric vaccine development include immunological heterogeneity among pathogen strains or isolates, a lack of animal challenge models to evaluate vaccine candidacy, undefined host immune correlates to protection, and a low protective efficacy among young children in endemic regions. In this article, we briefly updated the progress and challenges in vaccines and vaccine development for the leading enteric viral and bacterial pathogens including rotavirus, human calicivirus, Shigella, enterotoxigenic Escherichia coli (ETEC), cholera, nontyphoidal Salmonella, and Campylobacter, and introduced a novel epitope- and structure-based vaccinology platform known as MEFA (multiepitope fusion antigen) and the application of MEFA for developing broadly protective multivalent vaccines against heterogenous pathogens.

Detection and identification of adhesins involved in adhesion of Campylobacter jejuni to chicken skin

Campylobacter jejuni is the leading cause of bacterial food poisoning worldwide. Chickens are considered to be one of the major reservoirs of Campylobacter infection in humans due to colonization of their intestinal tract. When the chickens are slaughtered and processed, the entire skin of the carcass becomes contaminated with campylobacters. We observed that the number of C. jejuni attached to chicken skin was reduced significantly after treatment of the skin with sodium hydroxide followed by washing with PBS, implying that adhesion factors involved in binding to C. jejuni may exist on skin. Such potential binding-related proteins present in alkaline extracts of the skin surface were detected by a two-dimensional overlay assay and identified by liquid chromatography mass spectrometry (LC-MS). Chicken serum albumin (CSA) was identified as a major protein in these alkaline extracts and confirmed by ELISA to bind specifically to C. jejuni. Moreover, using the same approach, flagellar hook protein E (FlgE) and major outer membrane protein (MOMP) in C. jejuni were identified as bacterial adhesins that bound to the CSA. The ability to bind CSA was also confirmed using recombinant FlgE and MOMP of C. jejuni expressed in Escherichia coli. The present findings suggest that adhesins expressed on C. jejuni cells may bind specifically via proteins present on the skin, as well as by physical attachment.

Proteomics of Campylobacter jejuni Growth in Deoxycholate Reveals Cj0025c as a Cystine Transport Protein Required for Wild-type Human Infection Phenotypes

Campylobacter jejuni is a major cause of food-borne gastroenteritis. Proteomics by label-based two-dimensional liquid chromatography coupled to tandem mass spectrometry (LC-MS/MS) identified proteins associated with growth in 0.1% sodium deoxycholate (DOC, a component of gut bile salts), and system-wide validation was performed by data-independent acquisition (DIA-SWATH-MS). LC-MS/MS quantified 1326 proteins (∼82% of the predicted C. jejuni proteome), of which 1104 were validated in additional biological replicates by DIA-SWATH-MS. DOC resulted in a profound proteome shift with 512 proteins showing significantly altered abundance. Induced proteins were associated with flagellar motility and antibiotic resistance; and these correlated with increased DOC motility and resistance to polymyxin B and ciprofloxacin. DOC also increased human Caco-2 cell adherence and invasion. Abundances of proteins involved in nutrient transport were altered by DOC and aligned with intracellular changes to their respective carbon sources. DOC increased intracellular levels of sulfur-containing amino acids (cysteine and methionine) and the dipeptide cystine (Cys-Cys), which also correlated with reduced resistance to oxidative stress. A DOC induced transport protein was Cj0025c, which has sequence similarity to bacterial Cys-Cys transporters. Deletion of cj0025c (Δcj0025c) resulted in proteome changes consistent with sulfur starvation, as well as attenuated invasion, reduced motility, atypical morphology, increased antimicrobial susceptibility and poor biofilm formation. Targeted metabolomics showed Δcj0025c could use known C. jejuni amino and organic acid substrates commensurate with wild-type. Medium Cys-Cys levels however, were maintained in Δcj0025c relative to wild-type. A toxic Cys-Cys mimic (selenocystine) inhibited wild-type growth, but not Δcj0025c Provision of an alternate sulfur source (2 mm thiosulfate) restored Δcj0025c motility. Our data confirm that Cj0025c is a Cys-Cys transporter that we have named TcyP consistent with the nomenclature of homologous proteins in other species.

Antimicrobial Resistance and Virulence Properties of Campylobacter Spp. Originating from Domestic Geese in Poland

A total of 240 samples were evaluated for the presence of Campylobacter spp. Campylobacter was found in 83.3% of the cecum contents samples and 52.5% of the neck skin samples from carcasses. The prevailing species was C. jejuni, accounting for 87.7% of all Campylobacter isolates, and the remaining 12.3% of isolates were C. coli. All Campylobacter isolates, independent of the sample origin and species, were positive for 6 out of 15 tested genes (flaA, flhA, cadF, racR, ciaB, and cdtA genes). The prevalence of dnaJ, docA, pldA, cdtB, cdtC, and iam genes was also very common (ranging from 86.5% to 98.8%). The lowest prevalence was noted for virB11 and wlaN genes, both in Campylobacter isolates from cecum (12% and 19%) and carcasses (11.1% and 17.5%). None of the isolates tested, regardless of the sample origin, carried the cgtB gene. The highest resistance rates were observed for quinolones (90.8%) and tetracyclines (79.8%). Simultaneously, only single Campylobacter isolate was resistant to macrolides (0.6%) and none of the isolates showed resistance to aminoglycosides and amphenicols. The common presence of Campylobacter on geese carcasses as well as the detection of multidrug-resistant isolates indicate that consuming goose meat might cause a potential risk, therefore leading to human campylobacteriosis.

Mucosal delivery of live Lactococcus lactis expressing functionally active JlpA antigen induces potent local immune response and prevent enteric colonization of Campylobacter jejuni in chickens

Successful colonization of the mucosal epithelial cells is the key early step for Campylobacter jejuni (C. jejuni) pathogenesis in humans. A set of Surface Exposed Colonization Proteins (SECPs) are known to take leading role in bacterial adhesion and subsequent host pathogenesis. Among the major SECPs, the constitutively expressed C. jejuni surface lipoprotein Jejuni lipoprotein A (JlpA), interacts with intestinal heat shock protein 90α (Hsp90α) and contributes in disease progression by triggering pro-inflammatory responses via activation of NF-κB and p38 MAP kinase pathways. In addition to its ability to express on the surface, high sequence conservation of JlpA protein among different Campylobacter spp make it a suitable vaccine target against C. jejuni. Given that chickens are the primary source for C. jejuni infection in humans and persistent cecal colonization significantly contribute in pathogen transmission, we explicitly used chickens as a model to test the immune-protective efficacy of JlpA protein. Taking into account that gastro-intestinal tract is the major site for C. jejuni colonization, we chose to use mucosal (intragastric) route as mode for JlpA antigen delivery. To deliver JlpA via mucosal route, we engineered a food grade Lactic acid producing bacteria, Lactococcus lactis (L. lactis) to express functionally active JlpA protein in the surface. Further, we demonstrated its ability to substantially improve the antigen specific local immune responses in the intestine along with significant immune-protection against enteric colonization of C. jejuni in chickens.

Human Immunity Against Campylobacter Infection

Campylobacter is a worldwide foodborne pathogen, associated with human gastroenteritis. The efficient translocation of Campylobacter and its ability to secrete toxins into host cells are the 2 key features of Campylobacter pathophysiology which trigger inflammation in intestinal cells and contribute to the development of gastrointestinal symptoms, particularly diarrhoea, in humans. The purpose of conducting this literature review is to summarise the current understanding of: i) the human immune responses involved in the elimination of Campylobacter infection and ii) the resistance potential in Campylobacter against these immune responses. This review has highlighted that the intestinal epithelial cells are the preliminary cells which sense Campylobacter cells by means of their cell-surface and cytosolic receptors, activate various receptors-dependent signalling pathways, and recruit the innate immune cells to the site of inflammation. The innate immune system, adaptive immune system, and networking between these systems play a crucial role in bacterial clearance. Different cellular constituents of Campylobacter, mainly cell membrane lipooligosaccharides, capsule, and toxins, provide protection to Campylobacter against the human immune system mediated killing. This review has also identified gaps in knowledge, which are related to the activation of following during Campylobacter infection: i) cathelicidins, bactericidal permeability-increasing proteins, chemokines, and inflammasomes in intestinal epithelial cells; ii) siglec-7 receptors in dendritic cell; iii) acute phase proteins in serum; and iv) T-cell subsets in lymphoid nodules. This review evaluates the existing literature to improve the understanding of human immunity against Campylobacter infection and identify some of the knowledge gaps for future research.

Human campylobacteriosis: A public health concern of global importance

Campylobacter species are among the leading cause of bacterial foodborne and waterborne infections. In addition, Campylobacter is one of the major causative agent of bacterial gastrointestinal infections and the rise in the incidence of Campylobacter infections have been reported worldwide. Also, the emergence of some Campylobacter species as one of the main causative agent of diarrhea and the propensity of these bacteria species to resist the actions of antimicrobial agents; position them as a serious threat to the public health. This paper reviews Campylobacter pathogenicity, infections, isolation and diagnosis, their reservoirs, transmission pathways, epidemiology of Campylobacter outbreaks, prevention and treatment option, antibiotics resistance and control of antibiotics use.

A Novel Natural Antimicrobial Can Reduce the in vitro and in vivo Pathogenicity of T6SS Positive Campylobacter jejuni and Campylobacter coli Chicken Isolates

Human campylobacteriosis is considered one of the most common foodborne diseases worldwide with poultry identified as the main source of infection accounting for 50-80% of human cases. Highly virulent Campylobacter spp., positive for the Type VI secretion system (T6SS), which have an increased ability to adhere to and invade the host gastrointestinal epithelium are highly prevalent in poultry. Multidrug resistant strains of bacteria are rapidly evolving and therefore, new antimicrobials to supplement animal feed that are able to control Campylobacter species, are in great need. The work presented herein indicates that a novel phenolic antimicrobial, Auranta 3001, is able to reduce the adhesion and invasion of human intestinal epithelial cells (HCT-8) by two T6SS positive chicken isolates, C. jejuni RC039 (p < 0.05) and C. coli RC013 (p < 0.001). Exposure of C. jejuni RC039 and C. coli RC013 to Auranta 3001 downregulated the expression of hcp and cetB genes, known to be important in the functionality of T6SS. Furthermore, the reduced adhesion and invasion is associated with a significant decrease in bacterial motility of both isolates (p < 0.05-p < 0.001) in vitro. Most importantly our in vivo results show that Auranta 3001 is able to reduce cecum colonization levels from log 8 CFU/ml to log 2 CFU/ml for C. jejuni RC039 and from log 7 CFU/ml to log 2 CFU/ml for C. coli RC013. In conclusion, this novel antimicrobial is able to reduce the pathogenic properties of T6SS campylobacters in vitro and also to decrease colonization in vivo.

The Involvement of the Cas9 Gene in Virulence of Campylobacter jejuni

Campylobacter jejuni is considered as the leading cause of gastroenteritis all over the world. This bacterium has the CRISPR–cas9 system, which is used as a gene editing technique in different organisms. However, its role in bacterial virulence has just been discovered; that discovery, however, is just the tip of the iceberg. The purpose of this study is to find out the relationship between cas9 and virulence both phenotypically and genotypically in C. jejuni NCTC11168. Understanding both aspects of this relationship allows for a much deeper understanding of the mechanism of bacterial pathogenesis. The present study determined virulence in wild and mutant strains by observing biofilm formation, motility, adhesion and invasion, intracellular survivability, and cytotoxin production, followed by the transcriptomic analysis of both strains. The comparative gene expression profile of wild and mutant strains was determined on the basis of De-Seq transcriptomic analysis, which showed that the cas9 gene is involved in enhancing virulence. Differential gene expression analysis revealed that multiple pathways were involved in virulence, regulated by the CRISPR-cas9 system. Our findings help in understanding the potential role of cas9 in regulating the other virulence associated genes in C. jejuni NCTC11168. The findings of this study provide critical information about cas9's potential involvement in enhancing the virulence of C. jejuni, which is a major public health threat.

CapC, a Novel Autotransporter and Virulence Factor of Campylobacter jejuni

Campylobacter jejuni is recognized as an important causative agent of bacterial gastroenteritis in the developed world. Despite the identification of several factors contributing to infection, characterization of the virulence strategies employed by C. jejuni remains a significant challenge. Bacterial autotransporter proteins are a major class of secretory proteins in Gram-negative bacteria, and notably, many autotransporter proteins contribute to bacterial virulence. The aim of this study was to characterize the C. jejuni 81116 C8J_1278 gene (capC), predicted to encode an autotransporter protein, and examine the contribution of this factor to virulence of C. jejuni The predicted CapC protein has a number of features that are consistent with autotransporters, including the N-terminal signal sequence and the C-terminal β-barrel domain and was determined to localize to the outer membrane. Inactivation of the capC gene in C. jejuni 81116 and C. jejuni M1 resulted in reduced insecticidal activity in Galleria mellonella larvae. Furthermore, C. jejuni capC mutants displayed significantly reduced adherence to and invasion of nonpolarized, partially differentiated Caco-2 and T84 intestinal epithelial cells. Gentamicin treatment showed that the reduced invasion of the capC mutant is primarily caused by reduced adherence to intestinal epithelial cells, not by reduced invasion capability. C. jejuni capC mutants caused reduced interleukin 8 (IL-8) secretion from intestinal epithelial cells and elicited a significantly diminished immune reaction in Galleria larvae, indicating that CapC functions as an immunogen. In conclusion, CapC is a new virulence determinant of C. jejuni that contributes to the integral infection process of adhesion to human intestinal epithelial cells.IMPORTANCECampylobacter jejuni is a major causative agent of human gastroenteritis, making this zoonotic pathogen of significant importance to human and veterinary public health worldwide. The mechanisms by which C. jejuni interacts with intestinal epithelial cells and causes disease are still poorly understood due, in part, to the heterogeneity of C. jejuni infection biology. Given the importance of C. jejuni to public health, the need to characterize novel and existing virulence mechanisms is apparent. The significance of our research is in demonstrating the role of CapC, a novel virulence factor in C. jejuni that contributes to adhesion and invasion of the intestinal epithelium, thereby in part, addressing the dearth of knowledge concerning the factors involved in Campylobacter pathogenesis and the variation observed in the severity of human infection.

Function of Serine Protease HtrA in the Lifecycle of the Foodborne Pathogen Campylobacter jejuni

Campylobacter jejuni is a major food-borne zoonotic pathogen, responsible for a large proportion of bacterial gastroenteritis cases, as well as Guillian-Barré and Miller-Fisher syndromes. During infection, tissue damage is mainly caused by bacteria invading epithelial cells and traversing the intestinal barrier. C. jejuni is able to enter the lamina propria and the bloodstream and may move into other organs, such as spleen, liver, or mesenteric lymph nodes. However, the involved molecular mechanisms are not fully understood. C. jejuni can transmigrate effectively across polarized intestinal epithelial cells mainly by the paracellular route using the serine protease high-temperature requirement A (HtrA). However, it appears that HtrA has a dual function, as it also acts as a chaperone, interacting with denatured or misfolded periplasmic proteins under stress conditions. Here, we review recent progress on the role of HtrA in C. jejuni pathogenesis. HtrA can be transported into the extracellular space and cleaves cell-to-cell junction factors, such as E-cadherin and probably others, disrupting the epithelial barrier and enabling paracellular transmigration of the bacteria. The secretion of HtrA is a newly discovered strategy also utilized by other pathogens. Thus, secreted HtrA proteases represent highly attractive targets for anti-bacterial treatment and may provide a suitable candidate for vaccine development.

Cellular Tight Junctions Prevent Effective Campylobacter jejuni Invasion and Inflammatory Barrier Disruption Promoting Bacterial Invasion from Lateral Membrane in Polarized Intestinal Epithelial Cells

Campylobacter jejuni invasion is closely related to C. jejuni pathogenicity. The intestinal epithelium contains polarized epithelial cells that form tight junctions (TJs) to provide a physical barrier against bacterial invasion. Previous studies indicated that C. jejuni invasion of non-polarized cells involves several cellular features, including lipid rafts. However, the dynamics of C. jejuni invasion of polarized epithelial cells are not fully understood. Here we investigated the interaction between C. jejuni invasion and TJ formation to characterize the mechanism of C. jejuni invasion in polarized epithelial cells. In contrast to non-polarized epithelial cells, C. jejuni invasion was not affected by depletion of lipid rafts in polarized epithelial cells. However, depletion of lipid rafts significantly decreased C. jejuni invasion in TJ disrupted cells or basolateral infection and repair of cellular TJs suppressed lipid raft-mediated C. jejuni invasion in polarized epithelial cells. In addition, pro-inflammatory cytokine, TNF-α treatment that induce TJ disruption promote C. jejuni invasion and lipid rafts depletion significantly reduced C. jejuni invasion in TNF-α treated cells. These data demonstrated that TJs prevent C. jejuni invasion from the lateral side of epithelial cells, where they play a main part in bacterial invasion and suggest that C. jejuni invasion could be increased in inflammatory condition. Therefore, maintenance of TJs integrity should be considered important in the development of novel therapies for C. jejuni infection.

Methods to Study Campylobacter jejuni Adherence to and Invasion of Host Epithelial Cells

Measuring bacterial adherence and invasion of cells in vitro has enabled researchers to dissect the interactions of Campylobacter jejuni with eukaryotic cells. Numerous C. jejuni virulence determinants and host cell factors that contribute to the process of adherence, invasion, and immune modulation have been identified utilizing in vitro adherence and invasion assays. In this chapter, we describe the evaluation of C. jejuni adherence to and invasion of HeLa cells using the gentamicin-protection assay.

Identification of a Large Family of Slam-Dependent Surface Lipoproteins in Gram-Negative Bacteria

The surfaces of many Gram-negative bacteria are decorated with soluble proteins anchored to the outer membrane via an acylated N-terminus; these proteins are referred to as surface lipoproteins or SLPs. In Neisseria meningitidis, SLPs such as transferrin-binding protein B (TbpB) and factor-H binding protein (fHbp) are essential for host colonization and infection because of their essential roles in iron acquisition and immune evasion, respectively. Recently, we identified a family of outer membrane proteins called Slam (Surface lipoprotein assembly modulator) that are essential for surface display of neisserial SLPs. In the present study, we performed a bioinformatics analysis to identify 832 Slam related sequences in 638 Gram-negative bacterial species. The list included several known human pathogens, many of which were not previously reported to possess SLPs. Hypothesizing that genes encoding SLP substrates of Slams may be present in the same gene cluster as the Slam genes, we manually curated neighboring genes for 353 putative Slam homologs. From our analysis, we found that 185 (~52%) of the 353 putative Slam homologs are located adjacent to genes that encode a protein with an N-terminal lipobox motif. This list included genes encoding previously reported SLPs in Haemophilus influenzae and Moraxella catarrhalis, for which we were able to show that the neighboring Slams are necessary and sufficient to display these lipoproteins on the surface of Escherichia coli. To further verify the authenticity of the list of predicted SLPs, we tested the surface display of one such Slam-adjacent protein from Pasteurella multocida, a zoonotic pathogen. A robust Slam-dependent display of the P. multocida protein was observed in the E. coli translocation assay indicating that the protein is a Slam-dependent SLP. Based on multiple sequence alignments and domain annotations, we found that an eight-stranded beta-barrel domain is common to all the predicted Slam-dependent SLPs. These findings suggest that SLPs with a TbpB-like fold are found widely in Proteobacteria where they exist with their interaction partner Slam. In the future, SLPs found in pathogenic bacteria can be investigated for their role in virulence and may also serve as candidates for vaccine development.

Application of β-Resorcylic Acid as Potential Antimicrobial Feed Additive to Reduce Campylobacter Colonization in Broiler Chickens

Campylobacter is one of the major foodborne pathogens that result in severe gastroenteritis in humans, primarily through consumption of contaminated poultry products. Chickens are the reservoir host of Campylobacter, where the pathogen colonizes the ceca, thereby leading to contamination of carcass during slaughter. A reduction in cecal colonization by Campylobacter would directly translate into reduced product contamination and risk of human infections. With increasing consumer demand for antibiotic free chickens, significant research is being conducted to discover natural, safe and economical antimicrobials that can effectively control Campylobacter colonization in birds. This study investigated the efficacy of in-feed supplementation of a phytophenolic compound, β-resorcylic acid (BR) for reducing Campylobacter colonization in broiler chickens. In two separate, replicate trials, day-old-chicks (Cobb500; n = 10 birds/treatment) were fed with BR (0, 0.25, 0.5, or 1%) in feed for a period of 14 days (n = 40/trial). Birds were challenged with a four-strain mixture of Campylobacter jejuni (∼10⁶ CFU/ml; 250 μl/bird) on day 7 and cecal samples were collected on day 14 for enumerating surviving Campylobacter in cecal contents. In addition, the effect of BR on the critical colonization factors of Campylobacter (motility, epithelial cell attachment) was studied using phenotypic assay, cell culture, and real-time quantitative PCR. Supplementation of BR in poultry feed for 14 days at 0.5 and 1% reduced Campylobacter populations in cecal contents by ∼2.5 and 1.7 Log CFU/g, respectively (P < 0.05). No significant differences in feed intake and body weight gain were observed between control and treatment birds fed the compound (P > 0.05). Follow up mechanistic analysis revealed that sub-inhibitory concentration of BR significantly reduced Campylobacter motility, attachment to and invasion of Caco-2 cells. In addition, the expression of C. jejuni genes coding for motility (motA, motB, fliA) and attachment (jlpA, ciaB) was down-regulated as compared to controls (P < 0.05). These results suggest that BR could potentially be used as a feed additive to reduce Campylobacter colonization in broilers.

Comprehensive Spatial Analysis of the Borrelia burgdorferi Lipoproteome Reveals a Compartmentalization Bias toward the Bacterial Surface

The Lyme disease spirochete Borrelia burgdorferi is unique among bacteria in its large number of lipoproteins that are encoded by a small, exceptionally fragmented, and predominantly linear genome. Peripherally anchored in either the inner or outer membrane and facing either the periplasm or the external environment, these lipoproteins assume varied roles. A prominent subset of lipoproteins functioning as the apparent linchpins of the enzootic tick-vertebrate infection cycle have been explored as vaccine targets. Yet, most of the B. burgdorferi lipoproteome has remained uncharacterized. Here, we comprehensively and conclusively localize the B. burgdorferi lipoproteome by applying established protein localization assays to a newly generated epitope-tagged lipoprotein expression library and by validating the obtained individual protein localization results using a sensitive global mass spectrometry approach. The derived consensus localization data indicate that 86 of the 125 analyzed lipoproteins encoded by B. burgdorferi are secreted to the bacterial surface. Thirty-one of the remaining 39 periplasmic lipoproteins are retained in the inner membrane, with only 8 lipoproteins being anchored in the periplasmic leaflet of the outer membrane. The localization of 10 lipoproteins was further defined or revised, and 52 surface and 23 periplasmic lipoproteins were newly localized. Cross-referencing prior studies revealed that the borrelial surface lipoproteome contributing to the host-pathogen interface is encoded predominantly by plasmids. Conversely, periplasmic lipoproteins are encoded mainly by chromosomal loci. These studies close a gap in our understanding of the functional lipoproteome of an important human pathogen and set the stage for more in-depth studies of thus-far-neglected spirochetal lipoproteins.IMPORTANCE The small and exceptionally fragmented genome of the Lyme disease spirochete Borrelia burgdorferi encodes over 120 lipoproteins. Studies in the field have predominantly focused on a relatively small number of surface lipoproteins that play important roles in the transmission and pathogenesis of this global human pathogen. Yet, a comprehensive spatial assessment of the entire borrelial lipoproteome has been missing. The current study newly identifies 52 surface and 23 periplasmic lipoproteins. Overall, two-thirds of the B. burgdorferi lipoproteins localize to the surface, while outer membrane lipoproteins facing the periplasm are rare. This analysis underscores the dominant contribution of lipoproteins to the spirochete's rather complex and adaptable host-pathogen interface, and it encourages further functional exploration of its lipoproteome.

Relaxation of DNA supercoiling leads to increased invasion of epithelial cells and protein secretion by Campylobacter jejuni

Invasion of intestinal epithelial cells by Campylobacter jejuni is a critical step during infection of the intestine by this important human pathogen. In this study we investigated the role played by DNA supercoiling in the regulation of invasion of epithelial cells and the mechanism by which this could be mediated. A significant correlation between more relaxed DNA supercoiling and an increased ability of C. jejuni strains to penetrate human epithelial cells was demonstrated. Directly inducing relaxation of DNA supercoiling in C. jejuni was shown to significantly increase invasion of epithelial cells. Mutants in the fibronectin binding proteins CadF and FlpA still displayed an increased invasion after treatment with novobiocin suggesting these proteins were not essential for the observed phenotype. However, a large increase in protein secretion from multiple C. jejuni strains upon relaxation of DNA supercoiling was demonstrated. This increase in protein secretion was not mediated by outer membrane vesicles and appeared to be dependent on an intact flagellar structure. This study identifies relaxation of DNA supercoiling as playing a key role in enhancing C. jejuni pathogenesis during infection of the human intestine and identifies proteins present in a specific invasion associated secretome induced by relaxation of DNA supercoiling.

Genomic Comparison of Campylobacter spp. and Their Potential for Zoonotic Transmission between Birds, Primates, and Livestock

Campylobacter is the leading cause of human gastroenteritis worldwide. Wild birds, including American crows, are abundant in urban, suburban, and agricultural settings and are likely zoonotic vectors of Campylobacter Their proximity to humans and livestock increases the potential spreading of Campylobacter via crows between the environment, livestock, and humans. However, no studies have definitively demonstrated that crows are a vector for pathogenic Campylobacter We used genomics to evaluate the zoonotic and pathogenic potential of Campylobacter from crows to other animals with 184 isolates obtained from crows, chickens, cows, sheep, goats, humans, and nonhuman primates. Whole-genome analysis uncovered two distinct clades of Campylobacter jejuni genotypes; the first contained genotypes found only in crows, while a second genotype contained "generalist" genomes that were isolated from multiple host species, including isolates implicated in human disease, primate gastroenteritis, and livestock abortion. Two major β-lactamase genes were observed frequently in these genomes (oxa-184, 55%, and oxa-61, 29%), where oxa-184 was associated only with crows and oxa-61 was associated with generalists. Mutations in gyrA, indicative of fluoroquinolone resistance, were observed in 14% of the isolates. Tetracycline resistance (tetO) was present in 22% of the isolates, yet it occurred in 91% of the abortion isolates. Virulence genes were distributed throughout the genomes; however, cdtC alleles recapitulated the crow-only and generalist clades. A specific cdtC allele was associated with abortion in livestock and was concomitant with tetO These findings indicate that crows harboring a generalist C. jejuni genotype may act as a vector for the zoonotic transmission of Campylobacter IMPORTANCE: This study examined the link between public health and the genomic variation of Campylobacter in relation to disease in humans, primates, and livestock. Use of large-scale whole-genome sequencing enabled population-level assessment to find new genes that are linked to livestock disease. With 184 Campylobacter genomes, we assessed virulence traits, antibiotic resistance susceptibility, and the potential for zoonotic transfer to observe that there is a "generalist" genotype that may move between host species.

A direct-sensing galactose chemoreceptor recently evolved in invasive strains of Campylobacter jejuni

A rare chemotaxis receptor, Tlp11, has been previously identified in invasive strains of Campylobacter jejuni, the most prevalent cause of bacterial gastroenteritis worldwide. Here we use glycan and small-molecule arrays, as well as surface plasmon resonance, to show that Tlp11 specifically interacts with galactose. Tlp11 is required for the chemotactic response of C. jejuni to galactose, as shown using wild type, allelic inactivation and addition mutants. The inactivated mutant displays reduced virulence in vivo, in a model of chicken colonization. The Tlp11 sensory domain represents the first known sugar-binding dCache_1 domain, which is the most abundant family of extracellular sensors in bacteria. The Tlp11 signalling domain interacts with the chemotaxis scaffolding proteins CheV and CheW, and comparative genomic analysis indicates a likely recent evolutionary origin for Tlp11. We propose to rename Tlp11 as CcrG, Campylobacter ChemoReceptor for Galactose.

The Journey of Lipoproteins Through the Cell: One Birthplace, Multiple Destinations

Bacterial lipoproteins are a very diverse group of proteins characterized by the presence of an N-terminal lipid moiety that serves as a membrane anchor. Lipoproteins have a wide variety of crucial functions, ranging from envelope biogenesis to stress response. In Gram-negative bacteria, lipoproteins can be targeted to various destinations in the cell, including the periplasmic side of the cytoplasmic or outer membrane, the cell surface or the external milieu. The sorting mechanisms have been studied in detail in Escherichia coli, but exceptions to the rules established in this model bacterium exist in other bacteria. In this chapter, we will present the current knowledge on lipoprotein sorting in the cell. Our particular focus will be on the surface-exposed lipoproteins that appear to be much more common than previously assumed. We will discuss the different targeting strategies, provide numerous examples of surface-exposed lipoproteins and discuss the techniques used to assess their surface exposure.

Outer membrane lipoprotein biogenesis: Lol is not the end

Bacterial lipoproteins are lipid-anchored proteins that contain acyl groups covalently attached to the N-terminal cysteine residue of the mature protein. Lipoproteins are synthesized in precursor form with an N-terminal signal sequence (SS) that targets translocation across the cytoplasmic or inner membrane (IM). Lipid modification and SS processing take place at the periplasmic face of the IM. Outer membrane (OM) lipoproteins take the localization of lipoproteins (Lol) export pathway, which ends with the insertion of the N-terminal lipid moiety into the inner leaflet of the OM. For many lipoproteins, the biogenesis pathway ends here. We provide examples of lipoproteins that adopt complex topologies in the OM that include transmembrane and surface-exposed domains. Biogenesis of such lipoproteins requires additional steps beyond the Lol pathway. In at least one case, lipoprotein sequences reach the cell surface by being threaded through the lumen of a beta-barrel protein in an assembly reaction that requires the heteropentomeric Bam complex. The inability to predict surface exposure reinforces the importance of experimental verification of lipoprotein topology and we will discuss some of the methods used to study OM protein topology.

Adhesion, Biofilm Formation, and Genomic Features of Campylobacter jejuni Bf, an Atypical Strain Able to Grow under Aerobic Conditions

Campylobacter jejuni is the leading cause of bacterial enteritis in Europe. Human campylobacteriosis cases are frequently associated to the consumption of contaminated poultry meat. To survive under environmental conditions encountered along the food chain, i.e., from poultry digestive tract its natural reservoir to the consumer's plate, this pathogen has developed adaptation mechanisms. Among those, biofilm lifestyle has been suggested as a strategy to survive in the food environment and under atmospheric conditions. Recently, the clinical isolate C. jejuni Bf has been shown to survive and grow under aerobic conditions, a property that may help this strain to better survive along the food chain. The aim of this study was to evaluate the adhesion capacity of C. jejuni Bf and its ability to develop a biofilm. C. jejuni Bf can adhere to abiotic surfaces and to human epithelial cells, and can develop biofilm under both microaerobiosis and aerobiosis. These two conditions have no influence on this strain, unlike results obtained with the reference strain C. jejuni 81-176, which harbors only planktonic cells under aerobic conditions. Compared to 81-176, the biofilm of C. jejuni Bf is more homogenous and cell motility at the bottom of biofilm was not modified whatever the atmosphere used. C. jejuni Bf whole genome sequence did not reveal any gene unique to this strain, suggesting that its unusual property does not result from acquisition of new genetic material. Nevertheless some genetic particularities seem to be shared only between Bf and few others strains. Among the main features of C. jejuni Bf genome we noticed (i) a complete type VI secretion system important in pathogenicity and environmental adaptation; (ii) a mutation in the oorD gene involved in oxygen metabolism; and (iii) the presence of an uncommon insertion of a 72 amino acid coding sequence upstream from dnaK, which is involved in stress resistance. Therefore, the atypical behavior of this strain under aerobic atmosphere may result from the combination of insertions and mutations. In addition, the comparison of mRNA transcript levels of several genes targeted through genome analysis suggests the modification of regulatory processes in this strain.

Polyphosphate kinases modulate Campylobacter jejuni outer membrane constituents and alter its capacity to invade and survive in intestinal epithelial cells in vitro

Campylobacter jejuni is the most prevalent cause of bacterial gastroenteritis worldwide. Polyphosphate kinases 1 and 2 (PPK1 and PPK2) regulate several cellular processes, including the biosynthesis of the bacterial cell wall. Despite their importance, whether PPK1 and PPK2 modulate the composition of C. jejuni outer membrane constituents (OMCs) and consequently impact its interaction with host cells remains unknown. Our comparative analysis between C. jejuni wild type, Δppk1, and Δppk2 strains showed qualitative and quantitative differences in the total OMC composition among these strains. Importantly, these OMC variations observed on the C. jejuni polyphosphate kinase mutants are directly related to their capacity to invade, survive, and alter the immune response of intestinal epithelial cells in vitro. Specifically, sub-fractionation of the C. jejuni OMC indicated that OMC proteins are uniquely associated with bacterial invasion, whereas C. jejuni OMC proteins, lipids, and lipoglycans are all associated with C. jejuni intracellular survival. This study provides new insights regarding the function of polyphosphate kinases and their role in C. jejuni infection.

Surface-Exposed Lipoproteins: An Emerging Secretion Phenomenon in Gram-Negative Bacteria

Bacterial lipoproteins are hydrophilic proteins that are anchored to a cell membrane by N-terminally linked fatty acids. It is widely believed that nearly all lipoproteins produced by Gram-negative bacteria are either retained in the inner membrane (IM) or transferred to the inner leaflet of the outer membrane (OM). Lipoproteins that are exposed on the cell surface have also been reported but are generally considered to be rare. Results from a variety of recent studies, however, now suggest that the prevalence of surface-exposed lipoproteins has been underestimated. In this review we describe the evidence that the surface exposure of lipoproteins in Gram-negative bacteria is a widespread phenomenon and discuss possible mechanisms by which these proteins might be transported across the OM.

Contact- and Protein Transfer-Dependent Stimulation of Assembly of the Gliding Motility Machinery in Myxococcus xanthus

Bacteria engage in contact-dependent activities to coordinate cellular activities that aid their survival. Cells of Myxococcus xanthus move over surfaces by means of type IV pili and gliding motility. Upon direct contact, cells physically exchange outer membrane (OM) lipoproteins, and this transfer can rescue motility in mutants lacking lipoproteins required for motility. The mechanism of gliding motility and its stimulation by transferred OM lipoproteins remain poorly characterized. We investigated the function of CglC, GltB, GltA and GltC, all of which are required for gliding. We demonstrate that CglC is an OM lipoprotein, GltB and GltA are integral OM β-barrel proteins, and GltC is a soluble periplasmic protein. GltB and GltA are mutually stabilizing, and both are required to stabilize GltC, whereas CglC accumulate independently of GltB, GltA and GltC. Consistently, purified GltB, GltA and GltC proteins interact in all pair-wise combinations. Using active fluorescently-tagged fusion proteins, we demonstrate that GltB, GltA and GltC are integral components of the gliding motility complex. Incorporation of GltB and GltA into this complex depends on CglC and GltC as well as on the cytoplasmic AglZ protein and the inner membrane protein AglQ, both of which are components of the gliding motility complex. Conversely, incorporation of AglZ and AglQ into the gliding motility complex depends on CglC, GltB, GltA and GltC. Remarkably, physical transfer of the OM lipoprotein CglC to a ΔcglC recipient stimulates assembly of the gliding motility complex in the recipient likely by facilitating the OM integration of GltB and GltA. These data provide evidence that the gliding motility complex in M. xanthus includes OM proteins and suggest that this complex extends from the cytoplasm across the cell envelope to the OM. These data add assembly of gliding motility complexes in M. xanthus to the growing list of contact-dependent activities in bacteria.

Motility facilitates a wide variety of processes such as virulence, biofilm formation and development in bacteria. Bacteria have evolved at least three mechanisms for motility on surfaces: swarming motility, twitching motility and gliding motility. Mechanistically, gliding motility is poorly understood. Here, we focused on four proteins in Myxococcus xanthus that are essential for gliding. We show that CglC is an outer membrane (OM) lipoprotein, GltB and GltA are integral OM β-barrel proteins, and GltC is a soluble periplasmic protein. GltB, GltA and GltC are components of the gliding motility complex, and CglC likely stimulates the integration of GltB and GltA into the OM. Moreover, CglC, in a cell-cell contact-dependent manner, can be transferred from a cglC⁺ donor to a ΔcglC mutant leading to stimulation of gliding motility in the recipient. We show that upon physical transfer of CglC, CglC stimulates the assembly of the gliding motility complex in the recipient. The data presented here adds to the growing list of cell-cell contact-dependent activities in bacteria by demonstrating that gliding motility can be stimulated in a contact-dependent manner by transfer of a protein that stimulates assembly of the gliding motility complexes.

Distribution of virulence-associated genes in a selection of Campylobacter isolates

This study tested 24 Campylobacter isolates for the presence of 35 virulence genes using the polymerase chain reaction. The target genes included those involved in motility (flaA, flaB, flhA, flhB, flgB, flgE2, fliM, fliY), chemotaxis (cheA, cheB, cheR, cheW, cheY, cheZ), cell adhesion (cadF, dnaJ, jlpA, pldA, racR, virB11), invasion (iamA, ciaB, ceuE), cytotoxin production (cdtA, cdtB, cdtC, wlaN), capsule (kpsM), multidrug and bile resistance (cmeA, cmeB, cmeC), stress response/survival (katA, sodB), and the iron uptake system (cfrA, fur). The motility genes (with the exception of flaB), the CmeABC efflux system, cdtABC genes, and the sodB gene were commonly distributed among Campylobacter strains while the virB11 and wlaN genes were rarely detected. Interestingly, the findings suggest that flaB is not essential for full motility and C. coli lacking the flhA gene may be highly invasive. This study provides additional information on the distribution of Campylobacter virulence factors and the effect of their presence/absence on adhesion and invasion. It will inform future studies designed to elucidate the exact mechanisms of pathogenesis in Campylobacter.

Campylobacter jejuni serine protease HtrA plays an important role in heat tolerance, oxygen resistance, host cell adhesion, invasion, and transmigration

Campylobacter jejuni is an important pathogen of foodborne illness. Transmigration across the intestinal epithelial barrier and invasion are considered as primary reasons for tissue damage triggered by C. jejuni. Using knockout mutants, it was shown that the serine protease HtrA may be important for stress tolerance and physiology of C. jejuni. HtrA is also secreted in the extra-cellular environment, where it can cleave junctional host cell proteins such as E-cadherin. Aim of the present study was to establish a genetic complementation system in two C. jejuni strains in order to introduce the wild-type htrA gene in trans, test known htrA phenotypes, and provide the basis to perform further mutagenesis. We confirm that reexpression of the htrA wild-type gene in ΔhtrA mutants restored the following phenotypes: 1) C. jejuni growth at high temperature (44 °C), 2) growth under high oxygen stress conditions, 3) expression of proteolytically active HtrA oligomers, 4) secretion of HtrA into the supernatant, 5) cell attachment and invasion, and 6) transmigration across polarized epithelial cells. These results establish a genetic complementation system for htrA in C. jejuni, exclude polar effects in the ΔhtrA mutants, confirm important HtrA properties, and permit the discovery and dissection of new functions.

Campylobacter virulence and survival factors

Despite over 30 years of research, campylobacteriosis is the most prevalent foodborne bacterial infection in many countries including in the European Union and the United States of America. However, relatively little is known about the virulence factors in Campylobacter or how an apparently fragile organism can survive in the food chain, often with enhanced pathogenicity. This review collates information on the virulence and survival determinants including motility, chemotaxis, adhesion, invasion, multidrug resistance, bile resistance and stress response factors. It discusses their function in transition through the food processing environment and human infection. In doing so it provides a fundamental understanding of Campylobacter, critical for improved diagnosis, surveillance and control.

Evaluation of passive immunotherapeutic efficacy of hyperimmunized egg yolk powder against intestinal colonization of Campylobacter jejuni in chickens

Campylobacter jejuni is a leading cause of foodborne bacterial gastroenteritis in human. Chickens are the reservoir host of C. jejuni, and contaminated chicken meat is an important source of human infection. Therefore, control of C. jejuni in chickens can have direct effect on human health. In this study we tested the passive immunotherapeutic efficacy of the chicken egg-yolk-derived antibodies, in the form of hyperimmunized egg yolk powder (HEYP), against 7 colonization-associated proteins of C. jejuni, namely, CadF (Campylobacter adhesion to fibronectin), FlaA (flagellar proteins), MOMP (major outer membrane protein), FlpA (fibronectin binding protein A), CmeC (Campylobacter multidrug efflux C), Peb1A (Campylobacter putative adhesion), and JlpA (Jejuni lipoprotein A). Three chicken experiments were performed. In each experiment, chickens were treated orally via feed supplemented with 10% (wt/wt) egg yolk powder. In experiment 1, chicken groups were experimentally infected with C. jejuni (10(8) cfu) followed by treatment with 5 HEYP (CadF, FlaA, MOMP, FlpA, CmeC) for 4 d either individually or as a cocktail containing equal parts of each HEYP. In experiment 2, chickens were treated for 21 d with cocktail containing equal parts of 7 HEYP before and after experimental infection with C. jejuni (10(8) cfu). In experiment 3, chickens were treated with feed containing a cocktail of 7 HEYP before and after (prophylaxis), and after (treatment) experimental infection with C. jejuni (10(5) cfu). Intestinal colonization of C. jejuni was monitored by culturing cecal samples from chickens euthanized at the end of each experiment. The results showed that there were no differences in the cecal colonization of C. jejuni between HEYP treated and nontreated control chickens, suggesting that use of HEYP at the dose and the regimens used in the current study is not efficacious in reducing C. jejuni colonization in chickens.

A novel mouse model of Campylobacter jejuni gastroenteritis reveals key pro-inflammatory and tissue protective roles for Toll-like receptor signaling during infection

Campylobacter jejuni is a major source of foodborne illness in the developed world, and a common cause of clinical gastroenteritis. Exactly how C. jejuni colonizes its host's intestines and causes disease is poorly understood. Although it causes severe diarrhea and gastroenteritis in humans, C. jejuni typically dwells as a commensal microbe within the intestines of most animals, including birds, where its colonization is asymptomatic. Pretreatment of C57BL/6 mice with the antibiotic vancomycin facilitated intestinal C. jejuni colonization, albeit with minimal pathology. In contrast, vancomycin pretreatment of mice deficient in SIGIRR (Sigirr^−/−), a negative regulator of MyD88-dependent signaling led to heavy and widespread C. jejuni colonization, accompanied by severe gastroenteritis involving strongly elevated transcription of Th1/Th17 cytokines. C. jejuni heavily colonized the cecal and colonic crypts of Sigirr^−/− mice, adhering to, as well as invading intestinal epithelial cells. This infectivity was dependent on established C. jejuni pathogenicity factors, capsular polysaccharides (kpsM) and motility/flagella (flaA). We also explored the basis for the inflammatory response elicited by C. jejuni in Sigirr^−/− mice, focusing on the roles played by Toll-like receptors (TLR) 2 and 4, as these innate receptors were strongly stimulated by C. jejuni. Despite heavy colonization, Tlr4^−/−/Sigirr^−/− mice were largely unresponsive to infection by C. jejuni, whereas Tlr2^−/−/Sigirr^−/− mice developed exaggerated inflammation and pathology. This indicates that TLR4 signaling underlies the majority of the enteritis seen in this model, whereas TLR2 signaling had a protective role, acting to promote mucosal integrity. Furthermore, we found that loss of the C. jejuni capsule led to increased TLR4 activation and exaggerated inflammation and gastroenteritis. Together, these results validate the use of Sigirr^−/− mice as an exciting and relevant animal model for studying the pathogenesis and innate immune responses to C. jejuni.

Research into the key virulence strategies of the bacterial pathogen Campylobacter jejuni, as well as the host immune responses that develop against this microbe have, in many ways, been limited by the lack of relevant animal models. Here we describe the use of Sigirr deficient (^−/−) mice as a model for C. jejuni pathogenesis. Not only do Sigirr^−/− mice develop significant intestinal inflammation in response to colonization by C. jejuni, but the ability of this pathogen to trigger gastroenteritis was dependent on key virulence factors. We also found that the induction of the inflammatory and Th1/Th17 immune responses to infection in these mice depended on specific Toll-like receptors, principally TLR4, which we identified as the main driver of inflammation. In contrast, TLR2 signaling was found to protect mucosal integrity, with Tlr2^−/−/Sigirr^−/− mice suffering exaggerated mucosal damage and inflammation. Notably, we found that C. jejuni's capsule helped conceal it from the host's immune system as its loss led to significantly increased activation of host TLRs and exaggerated gastroenteritis. Our research shows that the increased sensitivity of Sigirr^−/− mice can be used to generate a unique and exciting model that facilitates the study of C. jejuni pathogenesis as well as host immunity to this enteric pathogen.

Proteomic and genomic analysis reveals novel Campylobacter jejuni outer membrane proteins and potential heterogeneity

Gram-negative bacterial outer membrane proteins play important roles in the interaction of bacteria with their environment including nutrient acquisition, adhesion and invasion, and antibiotic resistance. In this study we identified 47 proteins within the Sarkosyl-insoluble fraction of Campylobacter jejuni 81-176, using LC-ESI-MS/MS. Comparative analysis of outer membrane protein sequences was visualised to reveal protein distribution within a panel of Campylobacter spp., identifying several C. jejuni-specific proteins. Smith-Waterman analyses of C. jejuni homologues revealed high sequence conservation amongst a number of hypothetical proteins, sequence heterogeneity of other proteins and several proteins which are absent in a proportion of strains.

A negative effect of Campylobacter capsule on bacterial interaction with an analogue of a host cell receptor

BACKGROUND

Campylobacter jejuni (C. jejuni) is the leading causative agent of bacterial gastrointestinal infections. The rise of antibiotic resistant forms of this pathogen necessitates the development of novel intervention strategies. One approach is the design of drugs preventing bacterial attachment to host cells. Although some putative C. jejuni adhesins have been identified, the molecular mechanisms of their interaction with host cells and their role in pathogenesis remain to be elucidated. C. jejuni adhesion may also be modulated by a bacterial capsule. However, the role of this structure in adhesion was not clear due to conflicting results published by different research groups. The aim of this study was to clarify the role of capsule in bacterial interaction with host cells by using an in vitro model of adhesion and an analogue of a host cell receptor.

RESULTS

In this study, we developed an in vitro bacterial adhesion assay, which was validated using various tests, including competitive inhibition studies, exoglycosydase treatment and site-directed mutagenesis. We demonstrate that PEB3 is one of the cell surface glycoproteins required for bacterial interaction with an analogue of a host cell receptor. In contrast, JlpA glycoprotein adhesin is not required for such interaction. We demonstrate that the production of capsule reduces bacterial attachment, and that the genes involved in capsule and PEB3 adhesin biosynthesis are differentially regulated.

CONCLUSIONS

In this study we report an in vitro model for the investigation of bacterial interaction with analogs of host cell receptors. The results suggest an interfering effect of capsule on bacterial attachment. In addition, using a liquid culture, we demonstrate differential expression of a gene involved in capsule production (kpsM) and a gene encoding a glycoprotein adhesin (peb3). Further studies are required in order to establish if these genes are also differentially regulated during the infection process. The results will assist in better understanding of the mechanism of pathogenesis of C. jejuni in general and the role of capsule in the process in particular.