L-glutamine protects against enterohemorrhagic Escherichia coli infection by inhibiting bacterial virulence and enhancing host defense concurrently.

Abstract

Enterohemorrhagic Escherichia coli (EHEC) can colonize the gastrointestinal tract and cause bloody diarrhea in children. Previous studies showed that its pathogenesis could be mediated by metabolites from both the host and microbiota. L-Glutamine (Gln) was found to be depleted in intestinal tissues as the main energy source according to previous studies. Hence, we aimed to determine the effects of Gln on EHEC infection and its underlying mode of action. In this study, a Gln-limited signal was found to activate the type 3 secretion system (T3SS), which is crucial for EHEC infection via perturbation of central metabolism. By shifting the phosphorylation of NtrC, a key regulator in bacterial nitrogen metabolism, Gln stimulates ler transcripts in a σS-PchA-dependent manner. Our in vivo experiments further demonstrated that Gln supplementation can reduce EHEC colonization in the gastrointestinal tract by repressing T3SS. Moreover, Gln could further attenuate bacterial infection by boosting host defense, which might be dependent on multiple pathways. Besides, our experiments demonstrated that Gln did not induce Shiga-like toxin (Stx) production or cause impairment of gut flora. In conclusion, our study presented evidence that Gln could act against EHEC infection by reducing bacterial virulence and strengthening host defense. Therefore, Gln serves as a promising therapeutic agent for EHEC infection. IMPORTANCE The type 3 secretion system (T3SS) was obtained in many Gram-negative bacterial pathogens, and it is crucial for their pathogenesis. Environmental signals were found to be involved in the expression regulation of T3SS, which was vital for successful bacterial infection in the host. Here, we discovered that L-glutamine (Gln), the most abundant amino acid in the human body, could repress enterohemorrhagic Escherichia coli (EHEC) T3SS expression via nitrogen metabolism and therefore had potential as an antivirulence agent. Our in vitro and in vivo evidence demonstrated that Gln could decline EHEC infection by attenuating bacterial virulence and enhancing host defense simultaneously. We repurpose Gln as a potential treatment for EHEC infection accordingly.