Three new serine-protease autotransporters of <i>Enterobacteriaceae</i> (SPATEs) from extra-intestinal pathogenic <i>Escherichia coli</i> and combined role of SPATEs for cytotoxicity and colonization of the mouse kidney

Abstract

Serine protease autotransporters of <i>Enterobacteriaceae</i> (SPATEs) are secreted proteins that contribute to virulence and function as proteases, toxins, adhesins, and/or immunomodulators. An extra-intestinal pathogenic <i>E. coli</i> (ExPEC) O1:K1 strain, QT598, isolated from a turkey, was shown to contain <i>vat, tsh</i>, and three uncharacterized SPATE-encoding genes. Uncharacterized SPATEs: Sha (<i><u>S</u></i>erine-protease <i><u>h</u></i>emagglutinin <i><u>a</u></i>utotransporter), TagB and TagC (<i><u>t</u></i>andem <i><u>a</u></i>utotransporter <i><u>g</u></i>enes <i>B</i> and <i>C</i>) were tested for activities including hemagglutination, autoaggregation, and cytotoxicity when expressed in <i>E. coli</i> K-12. Sha and TagB conferred autoaggregation and hemagglutination activities. TagB, TagC, and Sha all exhibited cytopathic effects on a bladder epithelial cell line. In QT598, <i>tagB</i> and <i>tagC</i> are tandemly encoded on a genomic island, and were present in 10% of UTI isolates and 4.7% of avian <i>E. coli</i>. Sha is encoded on a virulence plasmid and was present in 1% of UTI isolates and 20% of avian <i>E. coli</i>. To specifically examine the role of SPATEs for infection, the 5 SPATE genes were deleted from strain QT598 and tested for cytotoxicity. Loss of all five SPATEs abrogated the cytopathic effect on bladder epithelial cells, although derivatives producing any of the 5 SPATEs retained cytopathic activity. In mouse infections, <i>sha</i> gene-expression was up-regulated a mean of sixfold in the bladder compared to growth <i>in vitro</i>. Loss of either <i>tagBC</i> or <i>sha</i> did not reduce urinary tract colonization. Deletion of all 5 SPATEs, however, significantly reduced competitive colonization of the kidney supporting a cumulative role of SPATEs for QT598 in the mouse UTI model.