Fig. 3.

Pathogens and non-pathogens modulate intestinal metabolism differently. The metabolites produced by commensal (non-pathogenic) bacteria play a key role in maintaining gut homeostasis, and bacteriophages trim and tailor the bacterial population. The peritropic membrane comprises chitin and proteins. By secreting proteases and chitinases, bacterial pathogens can digest, and thus weaken, the peritrophic barrier, allowing these bacteria to invade the intestinal epithelium. Alternatively, a non-invasive pathogen might interrupt signaling between commensals and the host intestine by consuming commensal metabolites or producing virulence factors that mute host signaling pathways. If intestinal lipid metabolism is dysregulated, the resulting lipid droplets within enterocytes can provide a platform for replication of viruses that exploit these organelles, thus promoting viral superinfection.