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

ABSTRACT

Serine protease autotransporters of Enterobacteriaceae (SPATEs) are secreted proteins that contribute to virulence and function as proteases, toxins, adhesins, and/or immunomodulators. An extra-intestinal pathogenic E. coli (ExPEC) O1:K1 strain, QT598, isolated from a turkey, was shown to contain vat, tsh, and three uncharacterized SPATE-encoding genes. Uncharacterized SPATEs: Sha (Serine-protease hemagglutinin autotransporter), TagB and TagC (tandem autotransporter genes B and C) were tested for activities including hemagglutination, autoaggregation, and cytotoxicity when expressed in E. coli 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, tagB and tagC are tandemly encoded on a genomic island, and were present in 10% of UTI isolates and 4.7% of avian E. coli. Sha is encoded on a virulence plasmid and was present in 1% of UTI isolates and 20% of avian E. coli. 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, sha gene-expression was up-regulated a mean of sixfold in the bladder compared to growth in vitro. Loss of either tagBC or sha 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.

KEYWORDS:

• Escherichia coli
• Autotransporters
• serine protease autotransporter
• SPATE
• Toxins
• avian pathogenic E. coli
• mouse infection
• uropathogenic E. coli
• poultry

Acknowledgments

We thank E. Bonneil, manager at the proteomics platform of Université de Montréal for assistance with mass spectrometry and peptide analysis and Y. Lopez de Los Santos for assistance for 3-D model prediction comparison of autotransporters. Funding for this work was supported by NSERC Canada Discovery Grants 2014-06622 and 2019-06642 (C.M.D.) and a collaborative ACIP grant from the Institut Pasteur International Network (to A.T., S.G.-R., and C.M.D).

Disclosure statement

No potential conflict of interest was reported by the authors.

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Additional information

Funding

This work was supported by the Institut Pasteur [ACIP]; Natural Sciences and Engineering Research Council of Canada [2014-06622] and [2019-06642].