Introduction The development of gastric atrophy in C57BL/6 mice infected with Helicobacter felis is differentially regulated by signalling involving NF-κB1 and NF-κB2. After infection, more severe atrophy developed in Nfkb1^-/- mice than wild-type (WT), whilst Nfkb2^-/- mice were protected from atrophic gastritis. Previous studies have also shown that the development of H. pylori induced gastric pathology was delayed in INS-Gas mice maintained in germ free, compared to conventional animal house conditions. Consequently we hypothesised that the different phenotypes observed in H. felis infected mice lacking specific NF-κB proteins may be influenced by altered gastric microbiomes. We have therefore quantified the abundance of specific bacterial phyla in Nfkb1^-/-, Nfkb2^-/- and C57BL/6 mice with and without H. felis infection.

Methods Groups of 3 C57BL/6, Nfkb1-/- and Nfkb2-/- mice aged 6 weeks were infected with H. felis by gavage. Animals were euthanased at 12 weeks and gastric antral DNA was extracted. Total bacterial load and relative abundance of α-Proteobacteria, γ-Proteobacteria, Bacteriodetes, Firmicutes and Actinobacteria were determined by qPCR of 16S rDNA. H. felis colonisation was quantified by qPCR for Flaa, samples were normalised to murine Gapdh.

Results Untreated WT mice had 3.4 and 2.6 fold greater universal bacterial transcripts than Nfkb1-/- and Nfkb2-/- mice respectively. Actinobacteria abundance was 6.0 fold greater in untreated Nfkb1-/- mice cf WT and 7.0 times greater in Nfkb2-/- mice. α-Proteobacteria were 9.0 times more abundant in untreated Nfkb1-/- mice cf WT. H. felis infection of WT mice resulted in 5.6 and 16.7 fold increases in α-Proteobacteria and γ-Proteobacteria respectively cf uninfected mice. γ-Proteobacteria were more abundant in all infected groups, but significantly more so in Nfkb2-/- mice than others. This correlated with a 30 fold higher abundance of H. felis (Phylum: γ-Proteobacteria) in infected Nfkb2-/- compared to WT mice. Infected Nfkb2-/- mice also had a 3.3 fold greater abundance of Actinobacteria cf infected WT mice. No statistically significant differences were observed in the abundance of Firmicutes or Bacteroidetes.

Conclusion Constitution of the murine gastric antral microbiome is influenced both by Helicobacter felis infection and somatic deletion of NF-κB family members. Since deletion of NF-κB1 and NF-κB2 have been reported to alter susceptibility to H. felis induced gastric atrophy, these data support the hypothesis that specific differences in microbiota may be responsible for, or reflect this altered susceptibility. Further studies are needed to determine whether specific organisms influence the development of gastric pathology either individually or within complex communities.

Disclosure of Interest None Declared