Comparison of media for the selective culture of enteroinvasive Escherichia coli.

MacConkey, eosine-methylene blue, deoxycholate-citrate, salmonella-shigella, and xylose-lysine-deoxycholate agars were compared for their ability to support the growth and to facilitate the recovery of enteroinvasive Escherichia coli strains from artificially contaminated as well as from clinical faecal samples. When grown as pure cultures, the 78 enteroinvasive Escherichia coli strains, as a group, exhibited the same growth characteristics as did Shigella isolates ( n=59), i.e. both organisms grew more weakly than did Salmonella strains ( n=22) on the various selective plates but 4- to 10-fold better than normal Escherichia coli isolates ( n=53). Xylose-lysine-deoxycholate and deoxycholate-citrate plates were more effective in recovering enteroinvasive Escherichia coli from faecal samples than was salmonella-shigella agar. Likewise, xylose-lysine-deoxycholate agar, similar to the differentiating MacConkey and eosine-methylene blue agars, was less inhibitory for defined "sensitive" strains than were the selective media tested. Preincubating clinical faecal samples in selenite F or in gram-negative broth did not influence the recovery of enteroinvasive Escherichia coli significantly. These data show that the use of xylose-lysine-deoxycholate, in combination with MacConkey or eosine-methylene blue agar, provides the best chance for recovery of enteroinvasive Escherichia coli when randomly selecting colonies from faecal cultures for subsequent molecular or immunological identification assays.

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.

A colony blot immunoassay to detect enteroinvasive Escherichia coli and Shigella in water samples.

AIMS: The aim of the study was to develop a colony blot immunoassay to detect Shigella and enteroinvasive Escherichia coli (EIEC) in water. METHODS AND RESULTS: Spiked samples were filtered through nitrocellulose membranes. Colony prints on the filters were tested with a monoclonal antibody specific to IpaC, an antigen coded by the invasion plasmid of Shigella and EIEC. Invasive pathogens could be successfully detected with the technique, even in the presence of a large number of non-pathogenic bacterial cells. The method was significantly more sensitive in identifying pathogen-containing samples then the traditional culture-based approach. CONCLUSION: The IpaC-specific colony blot immunoassay is an inexpensive method for identifying the aetiological agents of bacillary dysentery in water samples. SIGNIFICANCE AND IMPACT OF THE STUDY: The technique could be particularly useful in detecting enteroinvasive E. coli which often remains undetected by bio- and serotyping.