Bacterial load comparison of enteroaggregative Escherichia coli (EAEC) by real-time PCR (qPCR) between children with diarrhea and asymptomatic infection

Introduction Enteroaggregative Escherichia coli (EAEC) is a pathotype of diarrheagenic E. coli (DEC) that causes acute and persistent diarrhea in children, HIV-infected patients and travelers. However, EAEC can also be isolated in people without diarrhea. The aim of this study was to evaluated if the EAEC bacterial load in stool samples is associated with diarrhea in comparison with asymptomatic infection. Methods We selected 165 stool samples (children with diarrhea: 80 and asymptomatic children: 85) that previously were identified as EAEC by Real-Time PCR for diagnostic of DEC from E. coli isolated from stool cultures. We extracted DNA from fecal samples using the cetyltrimethylammonium bromide (CTAB) method and standardized a qPCR to evaluate the bacterial load using EAEC strain 042. Results The detection limit of the qPCR was 10 copies of aggR gene (5 bacterias)/mg stool and the reaction efficiency was ≥93%. We found a higher bacterial load in patients with diarrhea (2.781, 95% CI: 688-6875) bacteria/mg feces] than in asymptomatic children (138, 95% CI: 75-306) bacteria/mg feces], including samples with single pathogen infection and co-infections. Among diarrheal samples, the bacterial load was higher in boys than girls and in children older than 18 months than younger. Conclusions EAEC load in stool samples are higher in children with diarrhea than in asymptomatic infection. This qPCR could be useful for studying the role of colonization in children living in endemic areas where the isolation of this pathogen is similar in both groups.