A Novel Small RNA Promotes Motility and Virulence of Enterohemorrhagic Escherichia coli O157:H7 in Response to Ammonium

Enterohemorrhagic Escherichia coli serotype O157:H7 (O157) is a critical, foodborne, human intestinal pathogen that causes severe acute hemorrhagic diarrhea, abdominal cramping, and even death. Small RNAs (sRNAs) are noncoding regulatory molecules that sense environmental changes and trigger various virulence-related signaling pathways; however, few such sRNAs have been identified in O157. Here, we report a novel sRNA, EsrF that senses high ammonium concentrations in the colon and enhances O157 pathogenicity by promoting bacterial motility and adhesion to host cells. Specifically, EsrF was found to directly interact with the 5′ untranslated regions of the flagellar biosynthetic gene, flhB, mRNA and increase its abundance, thereby upregulating expression of essential flagellar genes, including flhD, flhC, fliA, and fliC, leading to elevated O157 motility and virulence. Meanwhile, an infant rabbit model of O157 infection showed that deletion of esrF and flhB significantly attenuates O157 pathogenicity. Furthermore, NtrC—the response regulator of the NtrC/B two-component system—was found to exert direct, negative regulation of esrF expression. Meanwhile, high ammonium concentrations in the colon release the inhibitory effect of NtrC on esrF, thereby enhancing its expression and subsequently promoting bacterial colonization in the host colon. Our work reveals a novel, sRNA-centered, virulence-related signaling pathway in O157 that senses high ammonium concentrations. These findings provide novel insights for future research on O157 pathogenesis and targeted treatment strategies.