ABSTRACT: Small non-coding RNA (sRNA) molecules can modulate diverse bacterial functions ranging from carbon metabolism to virulence gene expression. Here, we used a series of deletion strains to probe a panel of seven conserved sRNAs (DsrA, RprA, OxyS, RyhB, MicF, MicC, and Spot 42) of Extraintestinal Pathogenic Escherichia coli (ExPEC) isolate UTI89 for effects on the response to oxidative stress. ExPEC strains are the primary etiologic agents of urinary tract infections, which consistently rank among the most common infectious diseases and are a leading cause of sepsis. In broth culture, each sRNA deletion knockout grew like the wild-type strain, whereas the spot42 (spf) and micC knockout strains were both markedly impaired in their ability to deal with oxidative stress generated by methyl viologen. UTI89ΔmicC had several additional in vitro and in vivo phenotypes important for pathogenesis. in vitro, the micC knockout had impaired motility, reduced association with and survival within bladder epithelial cells (BECs), and reduced resistance to human serum. in vivo, the micC knockout was defective in its ability to colonize and persist in the mouse urinary tract, gastrointestinal tract, and bloodstream. RNA sequencing of UTI89ΔmicC as well as micC overexpressed using an inducible plasmid revealed differential expression of many genes, especially within metabolism and motility pathways. Notably, expression of the maltose transport operon malEFG was significantly reduced in UTI89ΔmicC, as was expression of the structural flagellar genes flgC and flgE. ompC, the only known target of MicC, did not have increased expression in the deletion, but did have significantly decreased expression in the micC overexpression strain. Here, we demonstrate that the conserved ExPEC sRNA MicC serves as a critical regulator of both stress resistance and virulence in a mammalian host, extending further the enigmatic functions of this bacterial sRNA.
