Intestinal crypt cells and the microbiome undergo abrupt reprogramming at the onset of colonic infection

We used the mouse pathogen Citrobacter rodentium to model gut infections. Following oral inoculation C. rodentium resides in the caecum for the first 3 days, before it infects the colon on the 4th day. Here we show that while the host is unresponsive to the infection on day 3, there is an abrupt reprogramming of the cellular composition of the crypt, involving depletion of goblet and deep crypt secretory cells, as well as metabolism (e.g. simultaneous up-regulation of cholesterol biogenesis, import and efflux), DNA damage repair and proliferation, which correlated with Ki67 staining, on day 4. Reduction in the abundance of proteins involved in the TCA cycle and oxidative phosphorylation, leading to oxygenation of the gut, coincided with instant expansion of mucosal-associated Enterobacteriaceae. These results show that sensing a small number of pathogenic bacteria triggers immediate intrinsic changes to the epithelium physiology and the microbiota, which parallel innate gut immune responses.