Characterization of enteroinvasive Escherichia coli strains isolated from children with diarrhea in Chile.

Analysis of stool samples from 912 cases of diarrhea among Chilean infants and 1,112 controls resulted in the isolation of 17 enteroinvasive Escherichia coli (EIEC) strains from diarrhea cases (1.9%) and 3 EIEC from the asymptomatic controls (0.3%). Biochemical analysis of the 20 isolates showed variability among them. However, the majority were lysine decarboxylase negative and nonmotile and utilized sodium acetate. The strains belonged to the O groups 28ac, 124, 143, or 144 or were untypable with the antisera used. Most of them had conjugative plasmids which mediated multiple antibiotic resistance. There was a strong correlation in this group of strains between a positive Sereny test, the presence of a plasmid of 120 megadaltons, and hybridization with the invasiveness probe, an HindIII fragment derived from the plasmid pPS15A. The isolates had a wide range of plasmid profiles. Bioassays and colony and Southern hybridization tests with iron uptake DNA probes indicated that 80% of the EIEC strains produced aerobactin and expressed its receptor, the genes for which are known to be chromosomally located.