Figure 5: Sialic acid catabolism is required for maintaining E. coli colonization.

(a) Growth of parental E. coli, nanT mutant and ManX mutant in modified minimal media containing 10 mM of glucose or sialic acid. (b) Relative fitness of parental E. coli and nanT mutant in colonization of WT mice and (c) ST mice. Bacterial colonization fitness was determined by counting c.f.u. of serially diluted faecal faeces collected at indicated time points. In (b,c), data are shown as median±interquartile range. N=8, *P<0.05 (two-tailed Student’s t-test). (d) Competitive index was calculated as ratio of parental E. coli to nanT mutant in WT and ST mice over 10 days after administration. The data are represented as median value, and each dot indicates an individual animal. N=8, *P<0.05 (two-tailed Student’s t-test). (e) Levels of free Neu5Ac in the caecal fluid of control and DSS-challenged WT mice were determined by HPLC analysis. (f) Levels of free Neu5Ac in the caecal fluid of control (C), streptomycin- and vancomycin-treated mice measured 5 days post treatment. In (e,f), the data are represented as mean±s.e.m. from two independent experiments. N=6–8, *P<0.05 (ANOVA, Bonferroni’s multiple comparison test).