Sialylation of lipooligosaccharide cores affects immunogenicity and serum resistance of Campylobacter jejuni

Unveiling potential roles of earthworms in mitigating the presence of virulence factor genes in terrestrial ecosystems

Earthworms can redistribute soil microbiota, and thus might affect the profile of virulence factor genes (VFGs) which are carried by pathogens in soils. Nevertheless, the knowledge of VFG profile in the earthworm guts and its interaction with earthworm gut microbiome is still lacking. Herein, we characterized earthworm gut and soil microbiome and VFG profiles in natural and agricultural ecosystems at a national scale using metagenomics. VFG profiles in the earthworm guts significantly differed from those in the surrounding soils, which was mainly driven by variations of bacterial communities. Furthermore, the total abundance of different types of VFGs in the earthworm guts was about 20-fold lower than that in the soils due to the dramatic decline (also by approximately 20-fold) of VFG-carrying bacterial pathogens in the earthworm guts. Additionally, five VFGs related to nutritional/metabolic factors and stress survival were identified as keystones merely in the microbe-VFG network in the earthworm guts, implying their pivotal roles in facilitating pathogen colonization in earthworm gut microhabitats. These findings suggest the potential roles of earthworms in reducing risks related to the presence of VFGs in soils, providing novel insights into earthworm-based bioremediation of VFG contamination in terrestrial ecosystems.

Virulent properties and genomic diversity of Vibrio vulnificus isolated from environment, human, diseased fish

The incidence of Vibrio vulnificus infections, with high mortality rates in humans and aquatic animals, has escalated, highlighting a significant public health challenge. Currently, reliable markers to identify strains with high virulence potential are lacking, and the understanding of evolutionary drivers behind the emergence of pathogenic strains is limited. In this study, we analyzed the distribution of virulent genotypes and phenotypes to discern the infectious potential of V. vulnificus strains isolated from three distinct sources. Most isolates, traditionally classified as biotype 1, possessed the virulence-correlated gene-C type. Environmental isolates predominantly exhibited YJ-like alleles, while clinical and diseased fish isolates were significantly associated with the nanA gene and pathogenicity region XII. Hemolytic activity was primarily observed in the culture supernatants of clinical and diseased fish isolates. Genetic relationships, as determined by multiple-locus variable-number tandem repeat analysis, suggested that strains originating from the same source tended to cluster together. However, multilocus sequence typing revealed considerable genetic diversity across clusters and sources. A phylogenetic analysis using single nucleotide polymorphisms of diseased fish strains alongside publicly available genomes demonstrated a high degree of evolutionary relatedness within and across different isolation sources. Notably, our findings reveal no direct correlation between phylogenetic patterns, isolation sources, and virulence capabilities. This underscores the necessity for proactive risk management strategies to address pathogenic V. vulnificus strains emerging from environmental reservoirs.IMPORTANCEAs the global incidence of Vibrio vulnificus infections rises, impacting human health and marine aquacultures, understanding the pathogenicity of environmental strains remains critical yet underexplored. This study addresses this gap by evaluating the virulence potential and genetic relatedness of V. vulnificus strains, focusing on environmental origins. We conduct an extensive genotypic analysis and phenotypic assessment, including virulence testing in a wax moth model. Our findings aim to uncover genetic and evolutionary factors that drive pathogenic strain emergence in the environment. This research advances our ability to identify reliable virulence markers and understand the distribution of pathogenic strains, offering significant insights for public health and environmental risk management.

Genomic Characterization of Campylobacter jejuni Associated with Perimyocarditis: A Family Case Report

Campylobacter spp. is the leading cause of foodborne gastrointestinal infections in humans worldwide. This study reports the first case of four family members who had contact with the same source of Campylobacter jejuni contamination with different results. Only the little siblings were infected by the same C. jejuni strain, but with different symptoms. Whereas the daughter was slightly affected with mild enteritis, the son suffered a longer campylobacteriosis followed with a perimyocarditis. This is the first case of the youngest patient affected by C. jejuni-related perimyocarditis published to date. The genomes of both strains were characterized by whole-genome sequencing and compared with the C. jejuni NCTC 11168 genome to gain insights into the molecular features that may be associated with perimyocarditis. Various comparison tools were used for the comparative genomics analysis, including the identification of virulence and antimicrobial resistance genes, phase variable (PV) genes, and single nucleotide polymorphisms (SNPs) identification. Comparisons of the strains identified 16 SNPs between them, which constituted small but significant changes mainly affecting the ON/OFF state of PV genes after passing through both hosts. These results suggest that PV occurs during human colonization, which modulates bacteria virulence through human host adaptation, which ultimately is related to complications after a campylobacteriosis episode depending on the host status. The findings highlight the importance of the relation between host and pathogen in severe complications of Campylobacter infections.

Crystal structure of Campylobacter jejuni lipoprotein Cj1090c

In Gram-negative bacteria, lipopolysaccharide (LPS) is an essential component of the asymmetric outer membrane (OM). LptE is an OM lipoprotein that forms a complex with the β-barrel OM protein, LptD. Incorporation of LPS into the OM outer leaflet is essential for bacterial viability, and mediated by the LptD/E complex. The genome of Campylobacter jejuni, a major foodborne pathogen, contains over 20 putative lipoproteins including Cj1090c. Here, we report the crystal structure of Cj1090c at 2.4 Å resolution, revealing structural evidence for LptE in C. jejuni. The analysis of this crystal structure, along with the genomic context, allows us to propose the C. jejuni LPS transport system for the first time, and permits for discussion of the features of the LptD/E complex of C. jejuni.

Biochemical and structural basis of sialic acid utilization by gut microbes

The human gastrointestinal (GI) tract harbors diverse microbial communities collectively known as the gut microbiota that exert a profound impact on human health and disease. The repartition and availability of sialic acid derivatives in the gut have a significant impact on the modulation of gut microbes and host susceptibility to infection and inflammation. Although N-acetylneuraminic acid (Neu5Ac) is the main form of sialic acids in humans, the sialic acid family regroups more than 50 structurally and chemically distinct modified derivatives. In the GI tract, sialic acids are found in the terminal location of mucin glycan chains constituting the mucus layer and also come from human milk oligosaccharides in the infant gut or from meat-based foods in adults. The repartition of sialic acid in the GI tract influences the gut microbiota composition and pathogen colonization. In this review, we provide an update on the mechanisms underpinning sialic acid utilization by gut microbes, focusing on sialidases, transporters, and metabolic enzymes.

Withdrawal of antibiotic growth promoters in China and its impact on the foodborne pathogen Campylobacter coli of swine origin

Antibiotic growth promoters (AGPs) have been used as feed additives to improve feed efficiency in food animals for more than six decades. However, the wide use of AGPs has led to the emergence of antibiotic-resistant pathogens of animal origin, posing a significant threat to food safety and public health. China prohibited the addition of AGPs to animal feed from July 2020. The impacts caused by the withdrawal of AGPs on the prevalence and antibiotic resistance of foodborne pathogens have not been illustrated. Here, a total of 471 strains of Campylobacter were isolated from pigs from three pig farms and two slaughterhouses in Sichuan Province for 4 consecutive years (2018–2021), including 2 years before and 2 years after the ban on AGPs in China. The isolation rate of Campylobacter had a slight increase after prohibiting the addition of AGPs to the feed. Contrary to what we expected, the antibiotic susceptibility test and WGS data showed that the antibiotic resistance to gentamicin and florfenicol and the abundance of virulence genes increased significantly after the ban of AGPs. Comparison of the isolates of swine origin with isolates of human origin indicated the potential of antibiotic-resistant Campylobacter transmission from pigs to humans. These data suggested that phasing out AGPs may lead to increased use of therapeutic antimicrobials, promoting the prevalence and transmission of both antibiotic resistance and virulence genes.

Zoonotic Transmission of Campylobacter jejuni to Caretakers From Sick Pen Calves Carrying a Mixed Population of Strains With and Without Guillain Barré Syndrome-Associated Lipooligosaccharide Loci

Campylobacter jejuni causes foodborne gastroenteritis and may trigger acute autoimmune sequelae including Guillain Barré Syndrome. Onset of neuromuscular paralysis is associated with exposure to C. jejuni lipooligosaccharide (LOS) classes A, B, C, D, and E that mimic and evoke antibodies against gangliosides on myelin and axons of peripheral nerves. Family members managing a Michigan dairy operation reported recurring C. jejuni gastroenteritis. Because dairy cattle are known to shed C. jejuni, we hypothesized that calves in the sick pen were the source of human infections. Fecal samples obtained from twenty-five calves, one dog, and one asymptomatic family member were cultured for Campylobacter. C. jejuni isolates were obtained from thirteen calves and the family member: C. coli from two calves, and C. hyointestinalis from two calves. Some calves had diarrhea; most were clinically normal. Typing of lipooligosaccharide biosynthetic loci showed that eight calf C. jejuni isolates fell into classes A, B, and C. Two calf isolates and the human isolate possessed LOS class E, associated mainly with enteric disease and rarely with Guillain Barré Syndrome. Multi-locus sequence typing, porA and flaA typing, and whole genome comparisons of the thirteen C. jejuni isolates indicated that the three LOS class E strains that included the human isolate were closely related, indicating zoonotic transmission. Whole-genome comparisons revealed that isolates differed in virulence gene content, particularly in loci encoding biosynthesis of surface structures. Family members experienced diarrheal illness repeatedly over 2 years, yet none experienced GBS despite exposure to calves carrying invasive C. jejuni with LOS known to elicit antiganglioside autoantibodies.

Common Adaptive Strategies Underlie Within-Host Evolution of Bacterial Pathogens

Within-host adaptation is a hallmark of chronic bacterial infections, involving substantial genomic changes. Recent large-scale genomic data from prolonged infections allow the examination of adaptive strategies employed by different pathogens and open the door to investigate whether they converge toward similar strategies. Here, we compiled extensive data of whole-genome sequences of bacterial isolates belonging to miscellaneous species sampled at sequential time points during clinical infections. Analysis of these data revealed that different species share some common adaptive strategies, achieved by mutating various genes. Although the same genes were often mutated in several strains within a species, different genes related to the same pathway, structure, or function were changed in other species utilizing the same adaptive strategy (e.g., mutating flagellar genes). Strategies exploited by various bacterial species were often predicted to be driven by the host immune system, a powerful selective pressure that is not species specific. Remarkably, we find adaptive strategies identified previously within single species to be ubiquitous. Two striking examples are shifts from siderophore-based to heme-based iron scavenging (previously shown for Pseudomonas aeruginosa) and changes in glycerol-phosphate metabolism (previously shown to decrease sensitivity to antibiotics in Mycobacterium tuberculosis). Virulence factors were often adaptively affected in different species, indicating shifts from acute to chronic virulence and virulence attenuation during infection. Our study presents a global view on common within-host adaptive strategies employed by different bacterial species and provides a rich resource for further studying these processes.

Structural and Biosynthetic Diversity of Nonulosonic Acids (NulOs) That Decorate Surface Structures in Bacteria

Nonulosonic acids (NulOs) are a diverse family of 9-carbon α-keto acid sugars that are involved in a wide range of functions across all branches of life. The family of NulOs includes the sialic acids as well as the prokaryote-specific NulOs. Select bacteria biosynthesize the sialic acid N-acetylneuraminic acid (Neu5Ac), and the ability to produce this sugar and its subsequent incorporation into cell-surface structures is implicated in a variety of bacteria-host interactions. Furthermore, scavenging of sialic acid from the environment for energy has been characterized across a diverse group of bacteria, mainly human commensals and pathogens. In addition to sialic acid, bacteria have the ability to biosynthesize prokaryote-specific NulOs, of which there are several known isomers characterized. These prokaryotic NulOs are similar in structure to Neu5Ac but little is known regarding their role in bacterial physiology. Here, we discuss the diversity in structure, the biosynthesis pathways, and the functions of bacteria-specific NulOs. These carbohydrates are phylogenetically widespread among bacteria, with numerous structurally unique modifications recognized. Despite the diversity in structure, the NulOs are involved in similar functions such as motility, biofilm formation, host colonization, and immune evasion.

Campylobacter sp.: Pathogenicity factors and prevention methods-new molecular targets for innovative antivirulence drugs?

Infections caused by bacterial species from the genus Campylobacter are one of the four main causes of strong diarrheal enteritis worldwide. Campylobacteriosis, a typical food-borne disease, can range from mild symptoms to fatal illness. About 550 million people worldwide suffer from campylobacteriosis and lethality is about 33 million p.a. This review summarizes the state of the current knowledge on Campylobacter with focus on its specific virulence factors. Using this knowledge, multifactorial prevention strategies can be implemented to reduce the prevalence of Campylobacter in the food chain. In particular, antiadhesive strategies with specific adhesion inhibitors seem to be a promising concept for reducing Campylobacter bacterial load in poultry production. Antivirulence compounds against bacterial adhesion to and/or invasion into the host cells can open new fields for innovative antibacterial agents. Influencing chemotaxis, biofilm formation, quorum sensing, secretion systems, or toxins by specific inhibitors can help to reduce virulence of the bacterium. In addition, the unusual glycosylation of the bacterium, being a prerequisite for effective phase variation and adaption to different hosts, is yet an unexplored target for combating Campylobacter sp. Plant extracts are widely used remedies in developing countries to combat infections with Campylobacter. Therefore, the present review summarizes the use of natural products against the bacterium in an attempt to stimulate innovative research concepts on the manifold still open questions behind Campylobacter towards improved treatment and sanitation of animal vectors, treatment of infected patients, and new strategies for prevention. KEY POINTS: • Campylobacter sp. is a main cause of strong enteritis worldwide. • Main virulence factors: cytolethal distending toxin, adhesion proteins, invasion machinery. • Strong need for development of antivirulence compounds.

Genomic epidemiology of Campylobacter jejuni associated with asymptomatic pediatric infection in the Peruvian Amazon

Campylobacter is the leading bacterial cause of gastroenteritis worldwide and its incidence is especially high in low- and middle-income countries (LMIC). Disease epidemiology in LMICs is different compared to high income countries like the USA or in Europe. Children in LMICs commonly have repeated and chronic infections even in the absence of symptoms, which can lead to deficits in early childhood development. In this study, we sequenced and characterized C. jejuni (n = 62) from a longitudinal cohort study of children under the age of 5 with and without diarrheal symptoms, and contextualized them within a global C. jejuni genome collection. Epidemiological differences in disease presentation were reflected in the genomes, specifically by the absence of some of the most common global disease-causing lineages. As in many other countries, poultry-associated strains were likely a major source of human infection but almost half of local disease cases (15 of 31) were attributable to genotypes that are rare outside of Peru. Asymptomatic infection was not limited to a single (or few) human adapted lineages but resulted from phylogenetically divergent strains suggesting an important role for host factors in the cryptic epidemiology of campylobacteriosis in LMICs.

Distribution of genes related to Type 6 secretion system and lipooligosaccharide that induced ganglioside mimicry among Campylobacter jejuni isolated from human diarrhea in Thailand

Background

Campylobacter jejuni (C. jejuni) is one of the most common bacteria responsible for human gastroenteritis worldwide. The mode of human transmission is foodborne infections due to consumption of contaminated food, especially poultry. Type 6 secretion systems (T6SS) were described recently as Campylobacter virulence mechanisms. Furthermore, infection sequelae associated with neurological disorders like Guillain-Barré (GBS) and Miller Fisher (MF) syndromes can become serious health problems in some patients after Campylobacter gastroenteritis. Our objective was to determine the distribution of these virulence genes among C. jejuni isolated from stool of human diarrhea.

Methods

A total of 524 C. jejuni strains from travelers and pediatric cases of acute diarrhea in Thailand were selected for this study. All isolates belonged to one of 20 known capsule types and all were assayed by PCR for T6SS, a hemolysin co-regulated protein (hcp) gene, and GBS-associated genes (cgtA, cgtB, cstII _HS19 and cstII _HS2 ) which are involved in sialic acid production in the lipooligosaccharide (LOS) cores of C. jejuni. The distribution of these genes are summarized and discussed.

Results

Of all isolates with these 20 capsule types identified, 328 (62.6%) were positive for hcp, ranging from 29.2 to 100% among 10 capsule types. The GBS-associated LOS genes were detected among 14 capsule type isolates with 24.4% and 23.3% of C. jejuni isolates possessed either cstII _HS19 or all three genes (cgtA, cgtB and cstII _HS19 ), which were classified as LOS classes A and B whereas 9.2% of C. jejuni isolates possessing cstII _HS2 were classified as LOS class C. The C. jejuni isolates of LOS A, B, and C together accounted for 56.9% of the isolates among 14 different capsule types while 31.1% of all C. jejuni isolates did not possess any GBS-associated genes. No significant difference was detected from C. jejuni isolates possessing GBS-associated LOS genes among travelers and children, but changes between those with hcp were significant (p < 0.05).

Conclusions

Our results suggested a high diversity of hcp and GBS-associated LOS genes among capsule types of C. jejuni isolated from Thailand.

Virulence Traits of Inpatient Campylobacter jejuni Isolates, and a Transcriptomic Approach to Identify Potential Genes Maintaining Intracellular Survival

There are still major gaps in our understanding of the bacterial factors that influence the outcomes of human Campylobacter jejuni infection. The aim of this study was to compare the virulence-associated features of 192 human C. jejuni strains isolated from hospitalized patients with diarrhoea (150/192, 78.1%), bloody diarrhoea (23/192, 11.9%), gastroenteritis (3/192, 1.6%), ulcerative colitis (3/192, 1.5%), and stomach ache (2/192, 1.0%). Traits were analysed with genotypic and phenotypic methods, including PCR and extracellular matrix protein (ECMP) binding, adhesion, and invasion capacities. Results were studied alongside patient symptoms, but no distinct links with them could be determined. Since the capacity of C. jejuni to invade host epithelial cells is one of its most enigmatic attributes, a high throughput transcriptomic analysis was performed in the third hour of internalization with a C. jejuni strain originally isolated from bloody diarrhoea. Characteristic groups of genes were significantly upregulated, outlining a survival strategy of internalized C. jejuni comprising genes related (1) to oxidative stress; (2) to a protective sheath formed by the capsule, LOS, N-, and O- glycosylation systems; (3) to dynamic metabolic activity supported by different translocases and the membrane-integrated component of the flagellar apparatus; and (4) to hitherto unknown genes.

Novel Clinical Campylobacter jejuni Infection Models Based on Sensitization of Mice to Lipooligosaccharide, a Major Bacterial Factor Triggering Innate Immune Responses in Human Campylobacteriosis

: Human Campylobacter jejuni infections inducing campylobacteriosis including post-infectious sequelae such as Guillain-Barré syndrome and reactive arthritis are rising worldwide and progress into a global burden of high socioeconomic impact. Intestinal immunopathology underlying campylobacteriosis is a classical response of the innate immune system characterized by the accumulation of neutrophils and macrophages which cause tissue destruction, barrier defects and malabsorption leading to bloody diarrhea. Clinical studies revealed that enteritis and post-infectious morbidities of human C. jejuni infections are strongly dependent on the structure of pathogenic lipooligosaccharides (LOS) triggering the innate immune system via Toll-like-receptor (TLR)-4 signaling. Compared to humans, mice display an approximately 10,000 times weaker TLR-4 response and a pronounced colonization resistance (CR) against C. jejuni maintained by the murine gut microbiota. In consequence, investigations of campylobacteriosis have been hampered by the lack of experimental animal models. We here summarize recent progress made in the development of murine C. jejuni infection models that are based on the abolishment of CR by modulating the murine gut microbiota and by sensitization of mice to LOS. These advances support the major role of LOS driven innate immunity in pathogenesis of campylobacteriosis including post-infectious autoimmune diseases and promote the preclinical evaluation of novel pharmaceutical strategies for prophylaxis and treatment.

Toxoplasma gondii Recruits Factor H and C4b-Binding Protein to Mediate Resistance to Serum Killing and Promote Parasite Persistence in vivo

Regulating complement is an important step in the establishment of infection by microbial pathogens. Toxoplasma gondii actively resists complement-mediated killing in non-immune human serum (NHS) by inactivating C3b, however the precise molecular basis is unknown. Here, a flow cytometry-based C3b binding assay demonstrated that Type II strains had significantly higher levels of surface-bound C3b than Type I strains. However, both strains efficiently inactivated C3b and were equally resistant to serum killing, suggesting that resistance is not strain-dependent. Toxoplasma activated both the lectin (LP) and alternative (AP) pathways, and the deposition of C3b was both strain and lectin-dependent. A flow cytometry-based lectin binding assay identified strain-specific differences in the level and heterogeneity of surface glycans detected. Specifically, increased lectin-binding by Type II strains correlated with higher levels of the LP recognition receptor mannose binding lectin (MBL). Western blot analyses demonstrated that Toxoplasma recruits both classical pathway (CP) and LP regulator C4b-binding proteins (C4BP) and AP regulator Factor H (FH) to the parasite surface to inactivate bound C3b-iC3b and C3dg and limit formation of the C5b-9 attack complex. Blocking FH and C4BP contributed to increased C5b-9 formation in vitro. However, parasite susceptibility in vitro was only impacted when FH was blocked, indicating that down regulation of the alternative pathway by FH may be more critical for parasite resistance. Infection of C3 deficient mice led to uncontrolled parasite growth, acute mortality, and reduced antibody production, indicating that both the presence of C3, and the ability of the parasite to inactivate C3, was protective. Taken together, our results establish that Toxoplasma regulation of the complement system renders mice resistant to acute infection by limiting parasite proliferation in vivo, but susceptible to chronic infection, with all mice developing transmissible cysts to maintain its life cycle.

Comparison of different technologies for the decipherment of the whole genome sequence of Campylobacter jejuni BfR-CA-14430

BACKGROUND

Campylobacter jejuni is a zoonotic pathogen that infects the human gut through the food chain mainly by consumption of undercooked chicken meat, raw chicken cross-contaminated ready-to-eat food or by raw milk. In the last decades, C. jejuni has increasingly become the most common bacterial cause for food-born infections in high income countries, costing public health systems billions of euros each year. Currently, different whole genome sequencing techniques such as short-read bridge amplification and long-read single molecule real-time sequencing techniques are applied for in-depth analysis of bacterial species, in particular, Illumina MiSeq, PacBio and MinION.

RESULTS

In this study, we analyzed a recently isolated C. jejuni strain from chicken meat by short- and long-read data from Illumina, PacBio and MinION sequencing technologies. For comparability, this strain is used in the German PAC-CAMPY research consortium in several studies, including phenotypic analysis of biofilm formation, natural transformation and in vivo colonization models. The complete assembled genome sequence most likely consists of a chromosome of 1,645,980 bp covering 1665 coding sequences as well as a plasmid sequence with 41,772 bp that encodes for 46 genes. Multilocus sequence typing revealed that the strain belongs to the clonal complex CC-21 (ST-44) which is known to be involved in C. jejuni human infections, including outbreaks. Furthermore, we discovered resistance determinants and a point mutation in the DNA gyrase (gyrA) that render the bacterium resistant against ampicillin, tetracycline and (fluoro-)quinolones.

CONCLUSION

The comparison of Illumina MiSeq, PacBio and MinION sequencing and analyses with different assembly tools enabled us to reconstruct a complete chromosome as well as a circular plasmid sequence of the C. jejuni strain BfR-CA-14430. Illumina short-read sequencing in combination with either PacBio or MinION can substantially improve the quality of the complete chromosome and epichromosomal elements on the level of mismatches and insertions/deletions, depending on the assembly program used.

Campylobacter jejuni: collective components promoting a successful enteric lifestyle

Campylobacter jejuni is the leading cause of bacterial diarrhoeal disease in many areas of the world. The high incidence of sporadic cases of disease in humans is largely due to its prevalence as a zoonotic agent in animals, both in agriculture and in the wild. Compared with many other enteric bacterial pathogens, C. jejuni has strict growth and nutritional requirements and lacks many virulence and colonization determinants that are typically used by bacterial pathogens to infect hosts. Instead, C. jejuni has a different collection of factors and pathways not typically associated together in enteric pathogens to establish commensalism in many animal hosts and to promote diarrhoeal disease in the human population. In this Review, we discuss the cellular architecture and structure of C. jejuni, intraspecies genotypic variation, the multiple roles of the flagellum, specific nutritional and environmental growth requirements and how these factors contribute to in vivo growth in human and avian hosts, persistent colonization and pathogenesis of diarrhoeal disease.

Domestication of Campylobacter jejuni NCTC 11168

Reference and type strains of well-known bacteria have been a cornerstone of microbiology research for decades. The sharing of well-characterized isolates among laboratories has run in parallel with research efforts and enhanced the reproducibility of experiments, leading to a wealth of knowledge about trait variation in different species and the underlying genetics. Campylobacter jejuni strain NCTC 11168, deposited at the National Collection of Type Cultures in 1977, has been adopted widely as a reference strain by researchers worldwide and was the first Campylobacter for which the complete genome was published (in 2000). In this study, we collected 23 C. jejuni NCTC 11168 reference isolates from laboratories across the UK and compared variation in simple laboratory phenotypes with genetic variation in sequenced genomes. Putatively identical isolates, identified previously to have aberrant phenotypes, varied by up to 281 SNPs (in 15 genes) compared to the most recent reference strain. Isolates also display considerable phenotype variation in motility, morphology, growth at 37 °C, invasion of chicken and human cell lines, and susceptibility to ampicillin. This study provides evidence of ongoing evolutionary change among C. jejuni isolates as they are cultured in different laboratories and highlights the need for careful consideration of genetic variation within laboratory reference strains. This article contains data hosted by Microreact.

Bacterial AB5 toxins inhibit the growth of gut bacteria by targeting ganglioside-like glycoconjugates

The AB₅ toxins cholera toxin (CT) from Vibrio cholerae and heat-labile enterotoxin (LT) from enterotoxigenic Escherichia coli are notorious for their roles in diarrheal disease, but their effect on other intestinal bacteria remains unexplored. Another foodborne pathogen, Campylobacter jejuni, can mimic the GM1 ganglioside receptor of CT and LT. Here we demonstrate that the toxin B-subunits (CTB and LTB) inhibit C. jejuni growth by binding to GM1-mimicking lipooligosaccharides and increasing permeability of the cell membrane. Furthermore, incubation of CTB or LTB with a C. jejuni isolate capable of altering its lipooligosaccharide structure selects for variants lacking the GM1 mimic. Examining the chicken GI tract with immunofluorescence microscopy demonstrates that GM1 reactive structures are abundant on epithelial cells and commensal bacteria, further emphasizing the relevance of this mimicry. Exposure of chickens to CTB or LTB causes shifts in the gut microbial composition, providing evidence for new toxin functions in bacterial gut competition.

Bacterial AB₅ toxins, such as cholera toxin, bind to oligosaccharides on the host cell surface and play key roles in the pathogenesis of diarrheal disease. Here, Patry et al. show that these toxins bind also to bacterial oligosaccharides and inhibit the growth of Campylobacter jejuni and gut commensal bacteria.

Genetics behind the Biosynthesis of Nonulosonic Acid-Containing Lipooligosaccharides in Campylobacter coli

Campylobacter jejuni and Campylobacter coli are the most common causes of bacterial gastroenteritis in the world. Ganglioside mimicry by C. jejuni lipooligosaccharide (LOS) is the triggering factor of Guillain-Barré syndrome (GBS), an acute polyneuropathy. Sialyltransferases from glycosyltransferase family 42 (GT-42) are essential for the expression of ganglioside mimics in C. jejuni Recently, two novel GT-42 genes, cstIV and cstV, have been identified in C. coli Despite being present in ∼11% of currently available C. coli genomes, the biological role of cstIV and cstV is unknown. In the present investigation, mutation studies with two strains expressing either cstIV or cstV were performed and mass spectrometry was used to investigate differences in the chemical composition of LOS. Attempts were made to identify donor and acceptor molecules using in vitro activity tests with recombinant GT-42 enzymes. Here we show that CstIV and CstV are involved in C. coli LOS biosynthesis. In particular, cstV is associated with LOS sialylation, while cstIV is linked to the addition of a diacetylated nonulosonic acid residue.IMPORTANCE Despite the fact that Campylobacter coli a major foodborne pathogen, its glycobiology has been largely neglected. The genetic makeup of the C. coli lipooligosaccharide biosynthesis locus was largely unknown until recently. C. coli harbors a large set of genes associated with lipooligosaccharide biosynthesis, including genes for several putative glycosyltransferases involved in the synthesis of sialylated lipooligosaccharide in Campylobacter jejuni In the present study, C. coli was found to express lipooligosaccharide structures containing sialic acid and other nonulosonate acids. These findings have a strong impact on our understanding of C. coli ecology, host-pathogen interaction, and pathogenesis.

Visible light sensitive Ag/TiO2/graphene composite as a potential coating material for control of Campylobacter jejuni

Infectious diarrhea caused by the food borne pathogen, Campylobacter jejuni, is a major threat to public health worldwide leads high incidence of child mortality each year. In the present study, hydrothermal synthesis of Silver-Graphene-TiO₂ nanocomposites along with TiO₂, TiO₂-Graphene and TiO₂-silver nanocomposites was done and the samples were characterized using X-ray diffraction (XRD), tunneling electron microscopy (TEM) and UV-Vis Spectroscopy. Effect of silver and graphene addition on the broad spectrum antibacterial ability of TiO₂ was studied under visible light. Moreover, the effects on bacterial survival, membrane integrity, cellular motiltiy and biofilm formation of C. jejuni were also evaluated. A synergetic effect of silver and graphene on Silver-Graphene-TiO₂ nanocomposites was observed as indicated by its increased visible light sensitivity and enhanced antibacterial activity under visible light compared to its parent derivatives. Silver-Graphene-TiO₂ composites effectively reduced growth and caused leakage of protein and DNA from C. jejuni cell. Atomic Force Microscopy was used to confirm bacterial cell damage. Besides, it also reduced motillity, hydrophobicity and autoaggregation of C. jejuni and showed excellent inhibition of biofilm formation. Furthermore, no significant cytotoxicity of synthesized nanoparticles was observed in human cell lines. We propose that Silver-Graphene-TiO₂ composites can be used as effective antimicrobial agents to control the spread of C. jejuni by preventing both bacterial growth and biofilm formation.

The Helicobacter pylori J99 jhp0106 Gene, under the Control of the CsrA/RpoN Regulatory System, Modulates Flagella Formation and Motility

CsrA has been shown to positively control the expression of flagella-related genes, including flaA and flaB, through regulating expression of an alternative sigma factor RpoN in Helicobacter pylori J99. Here, we aimed to characterize the CsrA regulatory system by comparative transcriptomic analysis carried out with RNA-seq on strain J99 and a csrA mutant. Fifty-three genes in the csrA mutant were found to be differentially expressed compared with the wild-type. Among CsrA-regulated genes, jhp0106, with unclear function, was found located downstream of flaB in the J99 genome. We hypothesized that flaB-jhp0106 is in an operon under the control of RpoN binding to the flaB promoter. The RT-qPCR results showed the expression of jhp0106 was decreased 76 and 92% in the csrA and rpoN mutants, respectively, compared to the wild-type. Moreover, mutations of the RpoN binding site in the flaB promoter region resulted in decreased expression of flaB and jhp0106 and deficient motility. Three-dimensional structure modeling results suggested that Jhp0106 was a glycosyltransferase. The role of jhp0106 in H. pylori was further investigated by constructing the jhp0106 mutant and revertant strains. A soft-agar motility assay and transmission electron microscope were used to determine the motility and flagellar structure of examined strains, and the results showed the loss of motility and flagellar structure in jhp0106 mutant J99. In conclusion, we found jhp0106, under the control of the CsrA/RpoN regulatory system, plays a critical role in H. pylori flagella formation.

DNA diversity of the wla gene cluster among serotype HS:19 and non-HS:19 Campylobacter jejuni strains

Campylobacter jejuni infection is an important trigger of Guillain-Barré syndrome (GBS), and serotype HS:19 strains are over-represented among GBS-associated isolates. Structures in C. jejuni lipooligosaccharide (LOS) resemble human gangliosides, suggesting that molecular mimicry could be important in triggering the neural injury. We assessed the genetic diversity among 36 C. jejuni serotype HS:19 and non-HS:19 strains by analysis of PCR-based restriction fragment length polymorphism (RFLP) patterns of 12 LOS biosynthesis-related genes ( wla cluster). PCR amplification revealed that the size, order, and direction of each wla gene was identical among all strains tested. However, an additional ORF, located between wlaI and wlaK, was detected in 28 of the 36 isolates examined, and nucleotide sequence analysis revealed that the gene was identical to orfE in C. jejuni strain NCTC 11168. An inverted repeat motif was found downstream of the wlaI stop codon and upstream of the orfE stop codon, an organization allowing pairing of repeated sequences that could lead to deletion of the internal segment. Digestion of the PCR products with restriction endonuclease DdeI or AluI and cluster analysis of RFLP banding patterns showed that all HS:19 strains were closely related and distinct from non-HS:19 strains, consistent with earlier analyses, suggesting that HS:19 strains represent a highly clonal population. RFLP analysis of wla genes also may be useful for epidemiological studies.

Michael F, Vinogradov EV, Stupak J, Zheng B, Ohnishi M, Unemo M, Lewis LA, Taylor RE, Landig CS, Diaz S, Reed GW, Varki A, Rice PA, Ram S. Utilizing CMP-Sialic Acid Analogs to Unravel Neisseria gonorrhoeae Lipooligosaccharide-Mediated Complement Resistance and Design Novel Therapeutics

Neisseria gonorrhoeae deploys a novel immune evasion strategy wherein the lacto-N-neotetraose (LNnT) structure of lipooligosaccharide (LOS) is capped by the bacterial sialyltransferase, using host cytidine-5’-monophosphate (CMP)-activated forms of the nine-carbon nonulosonate (NulO) sugar N-acetyl-neuraminic acid (Neu5Ac), a sialic acid (Sia) abundant in humans. This allows evasion of complement-mediated killing by recruiting factor H (FH), an inhibitor of the alternative complement pathway, and by limiting classical pathway activation (“serum-resistance”). We utilized CMP salts of six additional natural or synthetic NulOs, Neu5Gc, Neu5Gc8Me, Neu5Ac9Ac, Neu5Ac9Az, legionaminic acid (Leg5Ac7Ac) and pseudaminic acid (Pse5Ac7Ac), to define structural requirements of Sia-mediated serum-resistance. While all NulOs except Pse5Ac7Ac were incorporated into the LNnT-LOS, only Neu5Gc incorporation yielded high-level serum-resistance and FH binding that was comparable to Neu5Ac, whereas Neu5Ac9Az and Leg5Ac7Ac incorporation left bacteria fully serum-sensitive and did not enhance FH binding. Neu5Ac9Ac and Neu5Gc8Me rendered bacteria resistant only to low serum concentrations. While serum-resistance mediated by Neu5Ac was associated with classical pathway inhibition (decreased IgG binding and C4 deposition), Leg5Ac7Ac and Neu5Ac9Az incorporation did not inhibit the classical pathway. Remarkably, CMP-Neu5Ac9Az and CMP-Leg5Ac7Ac each prevented serum-resistance despite a 100-fold molar excess of CMP-Neu5Ac in growth media. The concomitant presence of Leg5Ac7Ac and Neu5Ac on LOS resulted in uninhibited classical pathway activation. Surprisingly, despite near-maximal FH binding in this instance, the alternative pathway was not regulated and factor Bb remained associated with bacteria. Intravaginal administration of CMP-Leg5Ac7Ac to BALB/c mice infected with gonorrhea (including a multidrug-resistant isolate) reduced clearance times and infection burden. Bacteria recovered from CMP-Leg5Ac7Ac-treated mice were sensitive to human complement ex vivo, simulating in vitro findings. These data reveal critical roles for the Sia exocyclic side-chain in gonococcal serum-resistance. Such CMP-NulO analogs may provide a novel therapeutic strategy against the global threat of multidrug-resistant gonorrhea.

Neisseria gonorrhoeae, the causative agent of the sexually transmitted infection gonorrhea, has developed widespread resistance to almost every conventional antibiotic currently in clinical use. Novel therapeutics are urgently needed against this pathogen. Gonococci have the capacity to scavenge CMP-N-acetyl-neuraminic acid (CMP-Neu5Ac, a CMP-activated 9-carbon sugar that is a member of the ‘sialic acid family’) from the host to ‘cap’ its lipooligosaccharide with Neu5Ac, which renders gonococci resistant to complement, a key arm of innate immune defenses. Here, we show that gonococci also utilize derivatives (or analogs) of CMP-Neu5Ac, which not only fail to render the bacteria resistant to complement, but also prevent complement inhibition mediated by the ‘physiologic’ human sialic acid donor, CMP-Neu5Ac. When administered intravaginally to mice, a representative analog significantly shortened the duration and burden of gonococcal infection. Thus, CMP-sialic acid analogs may represent promising preventive or therapeutic agents against multidrug-resistant gonorrhea that poses a global threat to public health.

Mass spectrometric analysis of products of metabolic glycan engineering with azido-modification of sialic acids

Metabolic engineering of glycans present on antibodies and other glycoproteins is becoming an interesting research area for improving our understanding of the glycome. With knowledge of the sialic acid biosynthetic pathways, the experiments described in this report are based on a published procedure involving the addition of a synthesized azido-mannosamine sugar into cell culture media and evaluation of downstream expression as azido-sialic acid. This unique bioorthogonal sugar has the potential for a variety of "click chemistry" reactions through the azide linkage, which allow for it to be isolated and quantified given the choice of label. In this report, mass spectrometry was used to investigate and optimize the cellular absorption of peracetylated N-azidoacetylmannosamine (Ac4ManNAz) to form N-azidoacetylneuraminic acid (SiaNAz) in a Chinese hamster ovary (CHO) cell line transiently expressing a double mutant trastuzumab (TZMm2), human galactosyltransferase 1 (GT), and human α-2,6-sialyltransferase (ST6). This in vivo approach is compared to in vitro enzymatic addition SiaNAz onto TZMm2 using soluble β-galactosamide α-2,6-sialyltransferase 1 and CMP-SiaNAz as donor. The in vivo results suggest that for this mAb, concentrations above 100 μM of Ac4ManNAz are necessary to allow for observation of terminal SiaNAz on tryptic peptides of TZMm2 by matrix-assisted laser desorption ionization (MALDI) mass spectrometry. This is further confirmed by a parallel study on the production of EG2-hFc monoclonal antibody (Zhang J et al. Prot Expr Purific 65(1); 77-82, 2009) in the presence of increasing concentrations of Ac4ManNAz.

Host-like carbohydrates promote bloodstream survival of Vibrio vulnificus in vivo

Sialic acids are found on all vertebrate cell surfaces and are part of a larger class of molecules known as nonulosonic acids. Many bacterial pathogens synthesize related nine-carbon backbone sugars; however, the role(s) of these non-sialic acid molecules in host-pathogen interactions is poorly understood. Vibrio vulnificus is the leading cause of seafood-related death in the United States due to its ability to quickly access the host bloodstream, which it can accomplish through gastrointestinal or wound infection. However, little is known about how this organism persists systemically. Here we demonstrate that sialic acid-like molecules are present on the lipopolysaccharide of V. vulnificus, are required for full motility and biofilm formation, and also contribute to the organism's natural resistance to polymyxin B. Further experiments in a murine model of intravenous V. vulnificus infection demonstrated that expression of nonulosonic acids had a striking benefit for bacterial survival during bloodstream infection and dissemination to other tissues in vivo. In fact, levels of bacterial persistence in the blood corresponded to the overall levels of these molecules expressed by V. vulnificus isolates. Taken together, these results suggest that molecules similar to sialic acids evolved to facilitate the aquatic lifestyle of V. vulnificus but that their emergence also resulted in a gain of function with life-threatening potential in the human host.

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.

Ubiquitous sialometabolism present among oral fusobacteria

Fusobacterium nucleatum is a ubiquitous member of the human oral flora and is associated with the development of periodontitis and a variety of other types of polymicrobial infections of the mucosa. In the oral cavity, this species is one of the few that is prevalent in both healthy and diseased subgingival plaque. Using microarray analysis, we examined the transcriptional response of F. nucleatum subspecies nucleatum to whole blood in order to identify some of the genetic responses that might occur during the transition from health to disease. From these studies, we identified a sialic acid catabolism operon that was induced by the presence of blood. We subsequently confirmed that this operon was inducible by the presence of synthetic sialic acid, but we found no evidence suggesting sialic acid was used as a major carbon source. However, this organism was found to possess a de novo synthesized surface sialylation ability that is widely conserved among the various F. nucleatum subspecies as well as in F. periodonticum. We provide evidence that fusobacterial sialylation does occur in the oral cavity irrespective of health status. Interestingly, only a minority of fusobacterial cells exhibit surface sialylation within dental plaque, whereas most cells are uniformly sialylated when grown in pure culture. The implications of these results are discussed.

The role of CRISPR-Cas systems in virulence of pathogenic bacteria

Clustered regularly interspaced short palindromic repeats (CRISPR) and CRISPR-associated (Cas) genes are present in many bacterial and archaeal genomes. Since the discovery of the typical CRISPR loci in the 1980s, well before their physiological role was revealed, their variable sequences have been used as a complementary typing tool in diagnostic, epidemiologic, and evolutionary analyses of prokaryotic strains. The discovery that CRISPR spacers are often identical to sequence fragments of mobile genetic elements was a major breakthrough that eventually led to the elucidation of CRISPR-Cas as an adaptive immunity system. Key elements of this unique prokaryotic defense system are small CRISPR RNAs that guide nucleases to complementary target nucleic acids of invading viruses and plasmids, generally followed by the degradation of the invader. In addition, several recent studies have pointed at direct links of CRISPR-Cas to regulation of a range of stress-related phenomena. An interesting example concerns a pathogenic bacterium that possesses a CRISPR-associated ribonucleoprotein complex that may play a dual role in defense and/or virulence. In this review, we describe recently reported cases of potential involvement of CRISPR-Cas systems in bacterial stress responses in general and bacterial virulence in particular.

Virulence characteristics of five new Campylobacter jejuni chicken isolates

Campylobacter enteritis has emerged as one of the most common forms of human diarrheal illness. In this study we have investigated the virulence potential of five new C. jejuni chicken isolates (RO14, RO19, RO24, RO29 and RO37) originated from private households in the rural regions of Banat and Transylvania in Romania. Following isolation and in vitro virulence assay, on HCT-8 cells, our results show that all the C. jejuni chicken isolates overcome the virulence abilities of the highly virulent strain C. jejuni 81-176. Motility, an important virulence factor was significantly improved in all the new chicken isolates. The ability to survive to the antimicrobial activity of the human serum, to resist to the violent attack of bile acids and to survive in the presence of synthetic antibiotics was increased in all the chicken isolates. However, these were statistically significant only for isolates RO29 and RO37. In conclusion our study shows, based on invasiveness and motility, and also on the data provided by the serum and bile resistance experiments that all the new chicken isolates are able to infect human cells, in vitro, and could potentially represent a health hazard for humans.

Lipooligosaccharide locus class of Campylobacter jejuni: sialylation is not needed for invasive infection

Campylobacter jejuni is a highly diverse enteropathogen that is commonly detected worldwide. It can sometimes cause bacteraemia, but the bacterial characteristics facilitating bloodstream infection are not known. A total of 73 C. jejuni isolates, consecutively collected from blood-borne infections during a 10-year period all over Finland and for which detailed clinical information of the patients were available, were included. We screened the isolates by PCR for the lipooligosaccharide (LOS) locus class and for the presence of the putative virulence genes ceuE, ciaB, fucP, and virB11. The isolates were also tested for γ-glutamyl transpeptidase production. The results were analysed with respect to the clinical characteristics of the patients, and the multilocus sequence types (MLSTs) and serum resistance of the isolates. LOS locus classes A, B, and C, which carry genes for sialylation of LOS, were detected in only 23% of the isolates. These isolates were not more resistant to human serum than those with the genes of non-sialylated LOS locus classes, but were significantly more prevalent among patients with underlying diseases (p 0.02). The fucose permease gene fucP was quite uncommon, but was associated with the isolates with the potential to sialylate LOS (p <0.0001). LOS locus classes and some of the putative virulence factors were associated with MLST clonal complexes. Although some of the bacterial characteristics studied here have been suggested to be important for the invasiveness of C. jejuni, they did not explain why the clinical isolates in the present study were able to cause bacteraemia.

Sialylation of Campylobacter jejuni endotoxin promotes dendritic cell-mediated B cell responses through CD14-dependent production of IFN-β and TNF-α

Campylobacter jejuni is the most common bacterial cause of human gastroenteritis and often precedes development of Guillain-Barré syndrome (GBS), a life-threatening paralytic disease. The incorporation of the carbohydrate sialic acid into C. jejuni lipooligosaccharides (LOS) is associated with increased severity of gastroenteritis and with induction of GBS; however, the underlying mechanisms remain completely unknown. In this study, we demonstrate that sialic acids in C. jejuni endotoxin enhance the rapid production of IFN-β and TNF-α by human dendritic cells (DCs). Using neutralizing Abs and receptors it was shown that these DC-derived cytokines promote the proliferation of human mucosal B cells in a T cell-independent manner. The production of both IFN-β and TNF-α by DCs in response to LOS requires CD14, and the amplified response of DCs to sialylated C. jejuni LOS is CD14 dependent. Together, these results indicate that sialylation of C. jejuni LOS increases DC activation and promotes subsequent B cell responses through CD14-driven production of IFN-β and TNF-α. This enhanced DC/B cell response may explain the increased pathogenicity of sialylated C. jejuni and may be key to the initiation of B cell-mediated autoimmunity in GBS.

The polysaccharide capsule of Campylobacter jejuni modulates the host immune response

Campylobacter jejuni is a major cause of bacterial diarrheal disease worldwide. The organism is characterized by a diversity of polysaccharide structures, including a polysaccharide capsule. Most C. jejuni capsules are known to be decorated nonstoichiometrically with methyl phosphoramidate (MeOPN). The capsule of C. jejuni 81-176 has been shown to be required for serum resistance, but here we show that an encapsulated mutant lacking the MeOPN modification, an mpnC mutant, was equally as sensitive to serum killing as the nonencapsulated mutant. A nonencapsulated mutant, a kpsM mutant, exhibited significantly reduced colonization compared to that of wild-type 81-176 in a mouse intestinal colonization model, and the mpnC mutant showed an intermediate level of colonization. Both mutants were associated with higher levels of interleukin 17 (IL-17) expression from lamina propria CD4(+) cells than from cells from animals infected with 81-176. In addition, reduced levels of Toll-like receptor 4 (TLR4) and TLR2 activation were observed following in vitro stimulation of human reporter cell lines with the kpsM and mpnC mutants compared to those with wild-type 81-176. The data suggest that the capsule polysaccharide of C. jejuni and the MeOPN modification modulate the host immune response.

Attenuation of Streptococcus suis virulence by the alteration of bacterial surface architecture

NeuB, a sialic acid synthase catalyzes the last committed step of the de novo biosynthetic pathway of sialic acid, a major element of bacterial surface structure. Here we report a functional NeuB homologue of Streptococcus suis, a zoonotic agent, and systematically address its molecular and immunological role in bacterial virulence. Disruption of neuB led to thinner capsules and more susceptibility to pH, and cps2B inactivation resulted in complete absence of capsular polysaccharides. These two mutants both exhibited increased adhesion and invasion to Hep-2 cells and improved sensibility to phagocytosis. Not only do they retain the capability of inducing the release of host pro-inflammatory cytokines, but also result in the faster secretion of IL-8. Easier cleaning up of the mutant strains in whole blood is consistent with virulence attenuation seen with experimental infections of both mice and SPF-piglets. Therefore we concluded that altered architecture of S. suis surface attenuates its virulence.

Sialoadhesin in recognition of self and non-self

The immune system is tightly regulated to maintain an appropriate balance between immune activation and tolerance. Macrophages play a key role in this process since they express many pathogen recognition molecules as well as receptors for 'self'. Sialoadhesin is a major macrophage receptor that specifically recognizes sialic acid, an abundant component of host glycoconjugates but which can also be found on several human pathogens. In recent years, several studies have demonstrated that sialoadhesin can contribute to the uptake and processing of sialylated pathogens as well as playing an important role in regulating inflammatory and autoimmune responses via recognition of self.

Characterization of α2,3- and α2,6-sialyltransferases from Helicobacter acinonychis

Genome sequence data were used to clone and express two sialyltransferase enzymes of the GT-42 family from Helicobacter acinonychis ATCC 51104, a gastric disease isolate from Cheetahs. The deposited genome sequence for these genes contains a large number of tandem repeat sequences in each of them: HAC1267 (RQKELE)(15) and HAC1268 (EEKLLEFKNI)(13). We obtained two clones with different numbers of repeat sequences for the HAC1267 gene homolog and a single clone for the HAC1268 gene homolog. Both genes could be expressed in Escherichia coli and sialyltransferase activity was measured using synthetic acceptor substrates containing a variety of terminal sugars. Both enzymes were shown to have a preference for N-acetyllactosamine, and they each made a product with a different linkage to the terminal galactose. HAC1267 is a mono-functional α2,3-sialyltransferase, whereas HAC1268 is a mono-functional α2,6-sialyltransferase and is the first member of GT-42 to show α2,6-sialyltransferase activity.

Sialylation of Campylobacter jejuni lipo-oligosaccharides: impact on phagocytosis and cytokine production in mice

Background

Guillain-Barré syndrome (GBS) is a post-infectious polyradiculoneuropathy, frequently associated with antecedent Campylobacter jejuni (C. jejuni) infection. The presence of sialic acid on C. jejuni lipo-oligosaccharide (LOS) is considered a risk factor for development of GBS as it crucially determines the structural homology between LOS and gangliosides, explaining the induction of cross-reactive neurotoxic antibodies. Sialylated C. jejuni are recognised by TLR4 and sialoadhesin; however, the functional implications of these interactions in vivo are unknown.

Methodology/Principal Findings

In this study we investigated the effects of bacterial sialylation on phagocytosis and cytokine secretion by mouse myeloid cells in vitro and in vivo. Using fluorescently labelled GM1a/GD1a ganglioside-mimicking C. jejuni strains and corresponding (Cst-II-mutant) control strains lacking sialic acid, we show that sialylated C. jejuni was more efficiently phagocytosed in vitro by BM-MΦ, but not by BM-DC. In addition, LOS sialylation increased the production of IL-10, IL-6 and IFN-β by both BM-MΦ and BM-DC. Subsequent in vivo experiments revealed that sialylation augmented the deposition of fluorescent bacteria in splenic DC, but not macrophages. In addition, sialylation significantly amplified the production of type I interferons, which was independent of pDC.

Conclusions/Significance

These results identify novel immune stimulatory effects of C. jejuni sialylation, which may be important in inducing cross-reactive humoral responses that cause GBS.

Campylobacter bacteremia: a rare and under-reported event?

Bacteria belonging to the species Campylobacter are the most common cause of bacterial diarrhoea in humans. The clinical phenotype associated with Campylobacter infections ranges from asymptomatic conditions to severe colitis and bacteremia. In susceptible patients, Campylobacter infections are associated with significant morbidity and mortality, with both host factors and bacterial factors being involved in the pathogenesis of bacteremia. In the host, age, gender and immune-compromising conditions may predispose for Campylobacter infections, whilst the most important bacterial determinants mentioned in the literature are cytotoxin production and flagellar motility. The role of sialylated lipo-oligosaccharide (LOS) and serum resistance in bacteremia is inconclusive at this time, and the clinical significance of Campylobacter bacteremia is not yet fully understood. More emphasis on the detection of Campylobacter species from blood cultures in susceptible patients at risk for Campylobacter infections will increase our understanding of the pathogenesis and the relevance of Campylobacter bacteremia.

The role of WlaRG, WlaTB and WlaTC in lipooligosaccharide synthesis by Campylobacter jejuni strain 81116

Campylobacter jejuni is a major bacterial cause of gastroenteritis world-wide. C. jejuni produces a range of glycans including lipooligosaccharide (LOS), an important virulence factor. The genetic content of the LOS synthesis locus varies between C. jejuni strains and 19 classes have been described. Three LOS synthesis genes of C. jejuni strain 81116 (NCTC 11828), wlaRG, wlaTB and wlaTC were the focus of this study. WlaRG and the remaining two proteins of interest share sequence similarity to aminotransferases and glycosyltransferases, respectively. These genes were insertionally inactivated and phenotypically characterised. Each mutant produced truncated LOS. Mutants lacking WlaRG, WlaTB and WlaTC produced LOS with reduced immunogenicity. Both the wlaRG and wlaTC mutants were non-motile and aflagellate. In vitro invasion and adhesion assays revealed that the wlaRG, wlaTB and wlaTC mutants displayed reduced adherence to chicken embryo fibroblasts. All mutants were less invasive of human cells than 81116 confirming the role of intact LOS during invasion of human cells in vitro. Here we propose the general composition for the 81116 LOS core backbone based on capillary electrophoresis-mass spectrometry.

Nontypeable Haemophilus influenzae: the role of N-acetyl-5-neuraminic acid in biology

Nontypeable Haemophilus influenzae (NTHi) is an exclusive human pathogen, which has evolved a number of unique mechanisms to survive within the human environment. An important part of this is the ability of the organism to take up and incorporate sialic acid into its surface structures. This protects the organism against host adaptive and innate immune factor as well as serving as a mechanism for sustaining itself within biofilms. Recent evidence suggests that this also may be the source of the evolution of human antibodies to non-human sialic acid structures, which can lead to inflammation in the host. In very rare instances, evolution of antibodies to sialylated lipooligosaccharide (LOS) mimics of human antigens can result in autoimmune disease.

Closely related Campylobacter jejuni strains from different sources reveal a generalist rather than a specialist lifestyle

Background

Campylobacter jejuni and Campylobacter coli are human intestinal pathogens of global importance. Zoonotic transmission from livestock animals or animal-derived food is the likely cause for most of these infections. However, little is known about their general and host-specific mechanisms of colonization, or virulence and pathogenicity factors. In certain hosts, Campylobacter species colonize persistently and do not cause disease, while they cause acute intestinal disease in humans.

Results

Here, we investigate putative host-specificity using phenotypic characterization and genome-wide analysis of genetically closely related C. jejuni strains from different sources. A collection of 473 fresh Campylobacter isolates from Germany was assembled between 2006 and 2010 and characterized using MLST. A subset of closely related C. jejuni strains of the highly prevalent sequence type ST-21 was selected from different hosts and isolation sources. PCR typing of strain-variable genes provided evidence that some genes differed between these strains. Furthermore, phenotypic variation of these strains was tested using the following criteria: metabolic variation, protein expression patterns, and eukaryotic cell interaction. The results demonstrated remarkable phenotypic diversity within the ST-21 group, which however did not correlate with isolation source. Whole genome sequencing was performed for five ST-21 strains from chicken, human, bovine, and food sources, in order to gain insight into ST-21 genome diversity. The comparisons showed extensive genomic diversity, primarily due to recombination and gain of phage-related genes. By contrast, no genomic features associated with isolation source or host were identified.

Conclusions

The genome information and phenotypic data obtained in vitro and in a chicken infection model provided little evidence of fixed adaptation to a specific host. Instead, the dominant C. jejuni ST-21 appeared to be characterized by phenotypic flexibility and high genetic microdiversity, revealing properties of a generalist. High genetic flexibility might allow generalist variants of C. jejuni to reversibly express diverse fitness factors in changing environments.

A tolerogenic mucosal immune response leads to persistent Campylobacter jejuni colonization in the chicken gut

Campylobacter enteritis is the most reported zoonotic disease in many developed countries where it imposes a serious health burden. Campylobacter transmission to humans occurs primarily through the chicken vector. Chicks are regarded as a natural host for Campylobacter species and are colonized with C. jejuni in particular. But despite carrying a very high bacterial load in their gastrointestinal tract, these birds, in contrast to humans, do not develop pathological signs. It seems that in chickens C. jejuni principally harbors in the cecal mucosal crypts, where an inefficient inflammatory response fails to clear the bacterium from the gut. Recent intensive research resulted in an increased insight into the cross talk between C. jejuni and its avian host. This review discusses the chicken intestinal mucosal immune response upon C. jejuni entrance, leading to tolerance and persistent cecal colonization. It might in addition provide a solid base for further research regarding this topic aiming to fully understand the host-bacterium dynamics of C. jejuni in chicks and to develop effective control measures to clear this zoonotic pathogen from poultry lines.

Colonization factors of Campylobacter jejuni in the chicken gut

Campylobacter contaminated broiler chicken meat is an important source of foodborne gastroenteritis and poses a serious health burden in industrialized countries. Broiler chickens are commonly regarded as a natural host for this zoonotic pathogen and infected birds carry a very high C. jejuni load in their gastrointestinal tract, especially the ceca. This eventually results in contaminated carcasses during processing. Current intervention methods fail to reduce the colonization of broiler chicks by C. jejuni due to an incomplete understanding on the interaction between C. jejuni and its avian host. Clearly, C. jejuni developed several survival and colonization mechanisms which are responsible for its highly adapted nature to the chicken host. But how these mechanisms interact with one another, leading to persistent, high-level cecal colonization remains largely obscure. A plethora of mutagenesis studies in the past few years resulted in the identification of several of the genes and proteins of C. jejuni involved in different aspects of the cellular response of this bacterium in the chicken gut. In this review, a thorough, up-to-date overview will be given of the survival mechanisms and colonization factors of C. jejuni identified to date. These factors may contribute to our understanding on how C. jejuni survival and colonization in chicks is mediated, as well as provide potential targets for effective subunit vaccine development.

Campylobacter capsule and lipooligosaccharide confer resistance to serum and cationic antimicrobials

The innate immune system plays a critical role in host defense against mucosal bacteria. Campylobacter jejuni is a major cause of human gastroenteritis that usually resolves spontaneously within several days, suggesting that innate mechanisms are important to control the infection. However, the specific means by which this occurs is not well understood. While diarrheal isolates of C. jejuni usually are susceptible to human serum, we found that a systemic strain of C. jejuni, isolated from the cerebrospinal fluid of an infant with meningitis, is relatively more resistant to human serum, the Bactericidal/Permeability-Increasing Protein (BPI), an endogenous cationic antimicrobial protein, and the cationic peptide antibiotic polymyxin B. To test the hypothesis that the surface properties of this strain contributed to its ability to withstand these innate host defenses, we constructed isogenic mutants in capsule (kpsM) and lipooligosaccharide (waaF) and complemented these mutants by insertion of the complementation construct in trans into hipO, a chromosomal locus. We found that capsule expression was essential for serum resistance, whereas lipooligosaccharide played no substantial role. In contrast, the lipooligosaccharide mutant showed increased sensitivity to polymyxin B, α-defensins, cathelicidins, and BPI. These findings suggest that the polysaccharides of C. jejuni strains contribute differently to resistance against host innate immunity; whereby capsule is more important for resisting human complement and lipooligosaccharide is more important for protection against killing mediated by cationic antimicrobial peptides and proteins.

Campylobacter jejuni proteins Cj0952c and Cj0951c affect chemotactic behaviour towards formic acid and are important for invasion of host cells

Campylobacter jejuni, an important food-borne bacterial pathogen in industrialized countries and in the developing world, is one of the major causes of bacterial diarrhoea. To identify genes which are important for the invasion of host cells by the pathogen, we screened altogether 660 clones of a transposon-generated mutant library based on the clinical C. jejuni isolate B2. Thereby, we identified a clone with a transposon insertion in gene cj0952c. As in the well-characterized C. jejuni strain NCTC 11168, the corresponding protein together with the gene product of the adjacent gene cj0951c consists of two transmembrane domains, a HAMP domain and a putative MCP domain, which together are thought to act as a chemoreceptor, designated Tlp7. In this report we show that genes cj0952c and cj0951c (i) are important for the host cell invasion of the pathogen, (ii) are not translated as one protein in C. jejuni isolate B2, contradicting the idea of a postulated read-through mechanism, (iii) affect the motility of C. jejuni, (iv) alter the chemotactic behaviour of the pathogen towards formic acid, and (v) are not related to the utilization of formic acid by formate dehydrogenase.

Effects of sequential Campylobacter jejuni 81-176 lipooligosaccharide core truncations on biofilm formation, stress survival, and pathogenesis

Campylobacter jejuni is a highly prevalent human pathogen for which pathogenic and stress survival strategies remain relatively poorly understood. We previously found that a C. jejuni strain 81-176 mutant defective for key virulence and stress survival attributes was also hyper-biofilm and hyperreactive to the UV fluorescent dye calcofluor white (CFW). We hypothesized that screening for CFW hyperreactive mutants would identify additional genes required for C. jejuni pathogenesis properties. Surprisingly, two such mutants harbored lesions in lipooligosaccharide (LOS) genes (waaF and lgtF), indicating a complete loss of the LOS outer core region. We utilized this as an opportunity to explore the role of each LOS core-specific moiety in the pathogenesis and stress survival of this strain and thus also constructed DeltagalT and DeltacstII mutants with more minor LOS truncations. Interestingly, we found that mutants lacking the LOS outer core (DeltawaaF and DeltalgtF but not DeltagalT or DeltacstII mutants) exhibited enhanced biofilm formation. The presence of the complete outer core was also necessary for resistance to complement-mediated killing. In contrast, any LOS truncation, even that of the terminal sialic acid (DeltacstII), resulted in diminished resistance to polymyxin B. The cathelicidin LL-37 was found to be active against C. jejuni, with the LOS mutants exhibiting modest but tiled alterations in LL-37 sensitivity. The DeltawaaF mutant but not the other LOS mutant strains also exhibited a defect in intraepithelial cell survival, an aspect of C. jejuni pathogenesis that has only recently begun to be clarified. Finally, using a mouse competition model, we now provide the first direct evidence for the importance of the C. jejuni LOS in host colonization. Collectively, this study has uncovered novel roles for the C. jejuni LOS, highlights the dynamic nature of the C. jejuni cell envelope, and provides insight into the contribution of specific LOS core moieties to stress survival and pathogenesis.

The role of endotoxin in infection: Helicobacter pylori and Campylobacter jejuni

Both Helicobacter pylori and Campylobacter jejuni are highly prevalent Gram-negative microaerophilic bacteria which are gastrointestinal pathogens of humans; H. pylori colonizes the gastroduodenal compartment and C. jejuni the intestinal mucosa. Although H. pylori causes chronic gastric infection leading to gastritis, peptic ulcers and eventually gastric cancer while C. jejuni causes acute infection inducing diarrhoeal disease, the endotoxin molecules of both bacterial species contrastingly contribute to their pathogenesis and the autoimmune sequelae each induces. Compared with enterobacterial endotoxin, that of H. pylori has significantly lower endotoxic and immuno-activities, the molecular basis for which is the underphosphorylation and underacylation of the lipid A component that interacts with immune receptors. This induction of low immunological responsiveness by endotoxin may aid the prolongation of H. pylori infection and therefore infection chronicity. On the other hand, this contrasts with acute infection-causing C. jejuni where overt inflammation contributes to pathology and diarrhoea production, and whose endotoxin is immunologically and endotoxically active. Futhermore, both H. pylori and C. jejuni exhibit molecular mimicry in the saccharide components of their endotoxins which can induce autoreactive antibodies; H. pylori expresses mimicry of Lewis and some ABO blood group antigens, C. jejuni mimicry of gangliosides. The former has been implicated in influencing the development of inflammation and gastric atrophy (a precursor of gastic cancer), the latter is central to the development of the neurological disorder Guillain-Barré syndrome. Both diseases raise important questions concerning infection-induced autoimmunity awaiting to be addressed.