A colony blot immune assay to identify enteroinvasive Escherichia coli and Shigella in stool samples.

Using an IpaC protein-specific monoclonal antibody a colony blot immune assay was developed for the identification of enteroinvasive Escherichia coli (EIEC) and Shigella in fecal specimens, and was evaluated in a field study. By screening the entire culture plates the colony blot assay was significantly more sensitive than the investigation of 16 randomly selected colonies from artificially contaminated fecal specimens. Among the 165 stool samples from 121 patients with diarrhea the immune assay detected IpaC expressing colonies in 16 out of the 17 specimens positive with a Shigella-, and EIEC-specific polymerase chain reaction targeting the ipaH gene. Guided by the colony blots, Shigella was isolated from 12, while EIEC from four of the samples. The IpaC-specific colony blot immune assay is a simple screening method to detect EIEC in stool samples for laboratories not equipped with molecular techniques.