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

Motility and chemotaxis in Campylobacter and Helicobacter

Flagellar motility of Campylobacter jejuni and Helicobacter pylori influences host colonization by promoting migration through viscous milieus such as gastrointestinal mucus. This review explores mechanisms C. jejuni and H. pylori employ to control flagellar biosynthesis and chemotactic responses. These microbes tightly control the activities of σ(54) and σ(28) to mediate ordered flagellar gene expression. In addition to phase-variable and posttranslational mechanisms, flagellar biosynthesis is regulated spatially and numerically so that only a certain number of organelles are placed at polar sites. To mediate chemotaxis, C. jejuni and H. pylori combine basic chemotaxis signal transduction components with several accessory proteins. H. pylori is unusual in that it lacks a methylation-based adaptation system and produces multiple CheV coupling proteins. Chemoreceptors in these bacteria contain nonconserved ligand binding domains, with several chemoreceptors matched to environmental signals. Together, these mechanisms allow for swimming motility that is essential for colonization.

Novel murine infection models provide deep insights into the "ménage à trois" of Campylobacter jejuni, microbiota and host innate immunity

Background

Although Campylobacter jejuni-infections have a high prevalence worldwide and represent a significant socioeconomic burden, it is still not well understood how C. jejuni causes intestinal inflammation. Detailed investigation of C. jejuni-mediated intestinal immunopathology is hampered by the lack of appropriate vertebrate models. In particular, mice display colonization resistance against this pathogen.

Methodology/Principal Findings

To overcome these limitations we developed a novel C. jejuni-infection model using gnotobiotic mice in which the intestinal flora was eradicated by antibiotic treatment. These animals could then be permanently associated with a complete human (hfa) or murine (mfa) microbiota. After peroral infection C. jejuni colonized the gastrointestinal tract of gnotobiotic and hfa mice for six weeks, whereas mfa mice cleared the pathogen within two days. Strikingly, stable C. jejuni colonization was accompanied by a pro-inflammatory immune response indicated by increased numbers of T- and B-lymphocytes, regulatory T-cells, neutrophils and apoptotic cells, as well as increased concentrations of TNF-α, IL-6, and MCP-1 in the colon mucosa of hfa mice. Analysis of MyD88^−/−, TRIF^−/−, TLR4^−/−, and TLR9^−/− mice revealed that TLR4- and TLR9-signaling was essential for immunopathology following C. jejuni-infection. Interestingly, C. jejuni-mutant strains deficient in formic acid metabolism and perception induced less intestinal immunopathology compared to the parental strain infection. In summary, the murine gut flora is essential for colonization resistance against C. jejuni and can be overcome by reconstitution of gnotobiotic mice with human flora. Detection of C. jejuni-LPS and -CpG-DNA by host TLR4 and TLR9, respectively, plays a key role in immunopathology. Finally, the host immune response is tightly coupled to bacterial formic acid metabolism and invasion fitness.

Conclusion/Significance

We conclude that gnotobiotic and “humanized” mice represent excellent novel C. jejuni-infection and -inflammation models and provide deep insights into the immunological and molecular interplays between C. jejuni, microbiota and innate immunity in human campylobacteriosis.

Sulphite : cytochrome c oxidoreductase deficiency in Campylobacter jejuni reduces motility, host cell adherence and invasion

Campylobacter jejuni lacks the enzyme phosphofructokinase and, consequently, is incapable of metabolizing glucose. Instead, the pathogen uses a number of other chemicals to serve as electron donors. Like chemolithotrophic bacteria, C. jejuni is able to respire sulphite in the presence of a sulphite : cytochrome c oxidoreductase (SOR) that is encoded by the genes cj0004c and cj0005c; the former encodes a monohaem cytochrome c oxidoreductase and the latter a molybdopterin oxidoreductase. After screening of a transposon-based mutant library, we identified a mutant with an insertion in gene cj0005c that was strongly reduced in its capacity to infect Caco2 cells. Further characterization of a corresponding non-random knockout mutant together with a complemented mutant and the parental strain showed the cj0005c-deficient mutant to exhibit clearly reduced motility and diminished adherence to host cells. Furthermore, the transcription of genes responsible for the synthesis of, in particular, legionaminic acid was downregulated and the mutant had a reduced capacity to autoagglutinate. In contrast, neither the proliferation of the mutant, nor its intracellular ATP content, was altered compared to the parental strain.

Epidemiological association of different Campylobacter jejuni groups with metabolism-associated genetic markers

In this study, multilocus sequence typing (MLST) was combined with the genetic detection of six genetic markers, ansB, dmsA, ggt, cj1585c, cjj81176-1367/71 (cj1365c), and the two-gene marker tlp7 (cj0951c plus cj0952c), to assess if their presence correlated with different C. jejuni clonal groups. Using a collection of 266 C. jejuni isolates from (in decreasing order of sample size) humans, chickens, cattle, and turkeys, it was further investigated whether the resulting genotypes correlated with the isolation source. We found combinations of the six marker genes to be mutually exclusive, and their patterns of presence or absence correlated to some degree with animal source. Together with MLST results, the obtained genotypes could be segregated into six groups. An association was identified for ansB, dmsA, and ggt with the MLST-clonal complexes (MLST-CC) 22, 42, 45, and 283, which formed the most prominent group, in which chickens were the most prevalent animal source. Two other groups, characterized by the presence of cj1585c, cjj81176-1367/71, and the two-gene marker tlp7, associated with either MLST-CC 21 or 61, were overrepresented in isolates of bovine origin. Mutually exclusive marker gene combinations were observed for ansB, dmsA, and ggt, typically found in CC 45 and the related CC 22, 42, and 283, whereas the other three marker genes were found mostly in CC 21, 48, and 206. The presence of the two-gene marker tlp7, which is typical for MLST 21 and 53 as well as for MLST-CC 61, strongly correlates with a bovine host; this is interpreted as an example of host adaptation. In cases of C. jejuni outbreaks, these genetic markers could be helpful for more effective source tracking.