Detection of virulent Shigella and enteroinvasive Escherichia coli by induction of the 43 kDa invasion plasmid antigen, ipaC.

The invasion plasmid antigen, ipaC (43 kDa) of Shigella spp. and enteroinvasive Escherichia coli (EIEC) could be induced in vitro by growing them in the presence of Congo red. An enzyme-linked immunosorbent assay (ELISA) using antibodies to the 43 kDa protein of Shigella has been developed for specific detection of virulent Shigella spp and EIEC. The test is independent of initial isolation of individual colonies. As few as 10(2) CFU/ml of virulent Shigella present in mixed cultures could be detected and concurrently their susceptibility to antibiotics could be analysed after an initial growth of 8-16 h in Congo red-containing medium. The test may prove useful in the diagnosis and treatment of bacillary dysentery caused either by Shigella or EIEC through their rapid identification and proper antimicrobial therapy.