Microbiology and diagnosis of infections with Shigella and enteroinvasive Escherichia coli.

The etiology of dysentery in Thailand and the existing methods of diagnosing infections with Shigella and enteroinvasive Escherichia coli (EIEC) are reviewed. The four Shigella species (S. dysenteriae, S. flexneri, S. boydii, and S. sonnei) are classically identified by culture of fecal specimens on selective media and testing of isolates for agglutination in species-specific antisera. DNA probes have been used to identify both lactose-fermenting and non-lactose-fermenting EIEC as well as Shigella isolates that do not agglutinate in antisera. These DNA probes are not necessary for the identification of Shigella if a competent bacteriology laboratory with shigella antisera is available. In Thailand Shigella and EIEC are isolated more often from children greater than 2 years of age than from younger children. The clinical illness associated with EIEC infections is similar to shigellosis. Fewer children with EIEC infections than with shigellosis, however, have occult blood in stool (36% vs. 82%) and more than 10 fecal leukocytes per high-power field (36% vs. 67%). Standard bacteriologic methods and testing of E. coli isolates for hybridization with the shigella/EIEC probe are currently the most sensitive means of diagnosing infections caused by these enteric pathogens. A more rapid method of identifying Shigella and EIEC infections in a situation where a bacteriology laboratory is not available will probably involve immunologic assays.