The Escherichia coli O157:H7 carbon starvation-inducible lipoprotein Slp contributes to initial adherence in vitro via the human polymeric immunoglobulin receptor

Authors: FEDORCHUK, CHRISTINE - Pennsylvania State University; Kudva, Indira; KARIYAWASAM, SUBHASHINIE - Pennsylvania State University

Submitted to: PLOS ONE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/17/2019
Publication Date: 6/12/2019
Citation: Fedorchuk, C., Kudva, I.T., Kariyawasam, S. 2019. The Escherichia coli O157:H7 carbon starvation-inducible lipoprotein Slp contributes to initial adherence in vitro via the human polymeric immunoglobulin receptor. PLoS One. 14(6):e0216791. https://doi.org/10.1371/journal.pone.0216791.
DOI: https://doi.org/10.1371/journal.pone.0216791

Interpretive Summary: Escherichia coli O157:H7 (O157) is a bacteria responsible for food-borne illness in humans with symptoms ranging from watery/bloody diarrhea to kidney failure in few cases. O157 has a particularly effective and well-characterized ‘intimate’ mechanism for attaching to human intestinal cells. However, prior to ‘intimate’ attachment there is a process of ‘superficial’ attachment, which is needed for the bacteria to stay long enough at a site on the intestinal wall before ‘intimately’ binding to it. This process of ‘superficial’ attachment is not well understood. Through our analyses we have found one O157 protein involved in ‘superficial’ attachment known as the carbon starvation-inducible lipoprotein or Slp. Slp interacts with a protein on the human intestinal cells called the polymeric immunoglobulin receptor or pIgR. O157 protein such as Slp, involved in ‘superficial’ attachment maybe targeted for therapeutic interventions, such as vaccines that could interfere with O157 attachment to human intestinal cells and hence prevent disease.

Technical Abstract: Escherichia coli O157:H7 is the most well-studied serotype of the enterohemorrhagic E. coli (EHEC) class of E. coli intestinal pathogens, responsible for outbreaks of serious foodborne illness worldwide each year. Adherence mechanisms are a critical component of pathogenesis, persistence in natural reservoirs, and environmental contamination. E. coli O157:H7 has a highly effective adherence operon (the LEE-Locus of Enterocyte Effacement) and its encoded intimate adherence mechanism is well characterized. However, factors involved in initial attachment are not well understood and adhesins provide potential targets for intervention and treatment strategies. In this study, we describe a mechanism of initial adherence used by E. coli O157:H7 in vitro. Primarily, we describe a bacterial protein not previously reported to be involved in adherence, Slp (carbon starvation-inducible lipoprotein) and its interactions with the human host protein polymeric immunoglobulin receptor (pIgR). The human pIgR has previously been shown to act as an adherence receptor for mucosal pathogens, and is highly expressed in the intestine. Following the observation of significant colocalization phenotypes by immunofluorescence microscopy, a co-immunoprecipitation (Co-IP) assay was done with a human recombinant Fc-tagged pIgR protein and E. coli O157:H7 proteins, which led to the identification of a bacterial protein (Slp) attaching to the pIgR. Slp is a small lipoprotein found in E. coli and Shigella species. Disruption of Slp expression through deletion of its encoding gene slp in E. coli O157:H7 produced a significant adherence deficiency to Caco-2 cells, especially at early time points associated with initial adherence. Plasmid complementation of the slp gene fully restored the wild-type phenotype. Furthermore, immunofluorescence microscopy revealed evidence that this interaction is specific for extra-intestinal pathogenic strains of E. coli. Additionally, deletion of slp gene resulted in the absence of the corresponding protein band in further Co-IP assays, with the slp complemented mutant strain restored the wild-type binding behavior. These data support the proposition that Slp significantly and directly contributes to initial adherence, with the pIgR protein as its proposed receptor.