Submitted to: Foodborne Pathogens and Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: December 12, 2011
Publication Date: April 1, 2012
Citation: Kudva, I.T. 2012. In vitro adherence patterns of Shigella serogroups to bovine recto-anal junction squamous epithelial (RSE) cells are similar to those of Escherichia coli O157. Foodborne Pathogens and Disease. 9(4):346-351. Interpretive Summary: Shigella species are foodborne pathogens that are transmitted to humans via the feco-oral route through fecally contaminated food and water. Thus far, house-flies have been implicated as transient carriers, but rarely have animals been associated with /identified as a reservoir for these human pathogens; a case of septicemia caused by Shigella sonnei in a calf and isolation of Shigella flexneri from slaughtered cattle were the only such reports. Given that cattle have been implicated as reservoirs of diverse enteric pathogens with human disease causing potential, and also given the relatedness of Shigella to E. coli, in both phylogeny and epidemiology, we sought to determine whether Shigella could specifically bind cells of bovine origin as a reflection of their ability to colonize cattle. In this context, we evaluated various Shigella serogroups in a novel adherence assay, recently standardized in our laboratory that uses the bovine recto-anal junction squamous epithelial (RSE) cells. Interestingly, Shigella serogroups A, B and D did adhere to the bovine RSE cells with Shigella serogroup D exhibiting a distinct adherence pattern in the presence of D+Mannose. We are currently dissecting the mechanisms by which Shigella adhere to bovine RSE cells and evaluating similarities to other enteric bacteria, especially E. coli O157 with the goal of identifying common therapeutic and pre-harvest modalities. Our observations warrant both experimental and epidemiological evaluation of Shigella serogroups A, B and D carriage in cattle.
Technical Abstract: The aim of this study was to determine whether Shigella species, which are human gastrointestinal pathogens, can adhere to cattle recto-anal junction squamous epithelial (RSE) cells using a recently standardized adherence assay, and to compare their adherence patterns to that of Escherichia coli O157. Shigella dysenteriae (serogroup A), S. flexneri (serogroup B), S. boydii (serogroup C), and S. sonnei (serogroup D) were tested in adherence assays using both RSE and HEp-2 cells, in the presence and absence of D+Mannose. E. coli O157, which specifically adheres to RSE cells in a Type I fimbriae-independent manner compared to other nonpathogenic E. coli strains, was used as a positive control. Shigella serogroups A, B, D, but not C, adhered to RSE cells with distinct adherence patterns in the presence of D+Mannose. No such distinction could be made between the four Shigella serogroups based on the HEp-2 cell adherence patterns. Thus, this study provides evidence that certain Shigella serogroups adhere to RSE cells in a manner that is similar to the adherence pattern of E. coli O157. The unexpected binding of these foodborne, human pathogens to cells of the bovine gastrointestinal tract raises the interesting probability of cattle being hitherto unknown reservoirs of Shigella, especially serogroups B and D. This concept warrants evaluation in cattle both experimentally and epidemiologically. Furthermore, these results are an excellent platform for studies of common mechanisms of adherence of human gastrointestinal pathogens to the bovine gastrointestinal tract. In this regard, we are presently evaluating adherence mechanisms that Shigella share with other enteric pathogens, especially E. coli O157.