[Accumulation of actin and adhesion to HEp-2 cells of strains of Escherichia coli isolated from children with diarrhea in Mendoza, Argentina]
Ortiz A. Ruttler M. Garcia B. Balbi L. Cruzado M. Risler N. Castro C.
Catedra de Quimica Biologica, Facultad de Ciencias Medicas, Universidad Nacional de Cuyo, Mendoza, Argentina.
E. coli strains are the major bacterial cause of diarrhea among children under 2 years of age residing in Mendoza, Argentina. Detection of diarrheogenic E. coli is made after coproculture, by agglutination tests using O-group antisera including most enteropathogenic E. coli (EPEC) serogroups and others often isolated in diarrhea. Although there are many O serogroups and H serotypes of E. coli strongly associated with infantile diarrhea, a number of studies have shown differences in the rate of isolation of EPEC between cases and controls using DNA probes. We compared the diagnosis of EPEC infections by traditional serogrouping tests with other detection methods using cell culture, involving the screening of isolates for adherence patterns to HEp-2 cells. A total of 140 isolates from children less than 24 months old with acute, persistent and chronic diarrhea and 40 isolates from controls were recovered. Three distinct patterns of adherence, termed localised (LA), diffuse (DA) and aggregative (EAgg) adherence were found. The fluorescence actin staining assay was used as indicative of the ability of some EPEC strains that produce attaching-effacing (A/E) lesions. Positive serogrouping strains were strongly associated with adherence (P = 0.0001). LA adherence pattern occurred in 11% of cases with acute diarrhea associated with these serogroups (P = 0.001) and children under 12 months (P = 0.0001). The FAS test was positive in 80% of them. EAgg adherence was found only in patients (20% P = 0.0001) and DA occurred both in cases (29%) and controls (2.5% P = 0.0001). Diagnosis of EPEC infections has traditionally been performed by identifying organisms belonging to a number of serogroups or serotypes epidemiologically linked to diarrhea. Evidence is presented in this paper to show that pathogenicity is not restricted to serogroups. Isolation of many adherent strains not belonging to traditional EPEC O serogroups, shows the need for alternative methods to be used to detect and identify E. coli.