Commonality and biosynthesis of the O-methyl phosphoramidate capsule modification in Campylobacter jejuni

In this study we investigated the commonality and biosynthesis of the O-methyl phosphoramidate (MeOPN) group found on the capsular polysaccharide (CPS) of Campylobacter jejuni. High resolution magic angle spinning NMR spectroscopy was used as a rapid, high throughput means to examine multiple isolates, analyze the cecal contents of colonized chickens, and screen a library of CPS mutants for the presence of MeOPN. Sixty eight percent of C. jejuni strains were found to express the MeOPN with a high prevalence among isolates from enteritis, Guillain Barré, and Miller-Fisher syndrome patients. In contrast, MeOPN was not observed for any of the Campylobacter coli strains examined. The MeOPN was detected on C. jejuni retrieved from cecal contents of colonized chickens demonstrating that the modification is expressed by bacteria inhabiting the avian gastrointestinal tract. In C. jejuni 11168H, the cj1415-cj1418 cluster was shown to be involved in the biosynthesis of MeOPN. Genetic complementation studies and NMR/mass spectrometric analyses of CPS from this strain also revealed that cj1421 and cj1422 encode MeOPN transferases. Cj1421 adds the MeOPN to C-3 of the beta-d-GalfNAc residue, whereas Cj1422 transfers the MeOPN to C-4 of D-glycero-alpha-L-gluco-heptopyranose. CPS produced by the 11168H strain was found to be extensively modified with variable MeOPN, methyl, ethanolamine, and N-glycerol groups. These findings establish the importance of the MeOPN as a diagnostic marker and therapeutic target for C. jejuni and set the groundwork for future studies aimed at the detailed elucidation of the MeOPN biosynthetic pathway.

NADPH oxidase-1 deficiency offers little protection in Salmonella typhimurium-induced typhlitis in mice

AIM

To test whether Nox1 plays a role in typhlitis induced by Salmonella enterica serovar Typhimurium (S. Tm) in a mouse model.

METHODS

Eight-week-old male wild-type (WT) and Nox1 knockout (KO) C57BL6/J (B6) mice were administered metronidazole water for 4 d to make them susceptible to S. Tm infection by the oral route. The mice were given plain water and administered with 4 different doses of S. Tm by oral gavage. The mice were followed for another 4 d. From the time of the metronidazole application, the mice were observed twice daily and weighed daily. The ileum, cecum and colon were removed for sampling at the fourth day post-inoculation. Portions of all three tissues were fixed for histology and placed in RNAlater for mRNA/cDNA preparation and quantitative real-time PCR. The contents of the cecum were recovered for estimation of S. Tm CFU.

RESULTS

We found Nox1-knockout (Nox1-KO) mice were not more sensitive to S. Tm colonization and infection than WT B6 mice. This conclusion is based on the following observations: (1) S. Tm-infection induced similar weight loss in Nox1-KO mice compared to WT mice; (2) the same S. Tm CFU was recovered from the cecal content of Nox1-KO and WT mice regardless of the inoculation dose, except the lowest inoculation dose (2 × 10⁶ CFU) for which the Nox1-KO had one-log lower CFU than WT mice; (3) there is no difference in cecal pathology between WT and Nox1-KO groups; and (4) there are no S. Tm infection-induced changes in gene expression levels (IL-1b, TNF-α, and Duox2) between WT and Nox1-KO groups. The Alpi gene expression was more suppressed by S. Tm treatment in WT than the Nox1-KO cecum.

CONCLUSION

Nox1 does not protect mice from S. Tm colonization. Nox1-KO provides a very minor protective effect against S. Tm infection. Using NOX1-specific inhibitors for colitis therapy should not increase risks in bacterial infection.