Diarrheagenic Escherichia coli carrying supplementary virulence genes are an important cause of moderate to severe diarrhoeal disease in Mexico

Abstract

Diarrheagenic Escherichia coli (DEC) cause acute and persistent diarrhoea worldwide, but little is known about their epidemiology in Mexico. We determined the prevalence of bacterial enteropathogens in 831 children with acute diarrhoea over a four-year period in Yucatan, Mexico. Six DEC supplementary virulence genes (SVG), mainly associated with enteroaggregative E. coli (EAEC), were sought in 3100 E. coli isolates. DEC was the most common bacterial enteropathogen (28%), surpassing Salmonella (12%) and Shigella (9%). Predominant DEC groups were diffusely adherent E. coli (DAEC) (35%), EAEC (24%), and enteropathogenic E. coli (EPEC) (19%). Among children with DEC infections, 14% had severe illness mainly caused by EPEC (26%) and DAEC (18%); 30% had moderate diarrhoea mainly caused by DAEC (36%), mixed DEC infections (33%) and EAEC (32%). DAEC was most prevalent during spring, while ETEC, EAEC and EPEC predominated in summer. EAEC was more frequent in children 6-24 months old than in those younger than 6 months of age (P = 0.008, OR = 4.2, 95% CI, 1.3-13.9). The presence of SVG dispersin, (aatA), dispersin-translocator (aatA), enteroaggregative heat-stable toxin 1 (astA), plasmid encoded toxin (pet), cytolethal distending toxin (cdt) was higher in DEC than non-DEC strains, (36% vs 26%, P <0.0001, OR = 1.5, 95% CI, 1.3-1.8). 98% of EAEC-infected children harboured strains with SVG; 85% carried the aap-aatA gene combination, and 33% of these also carried astA. 28% of both EPEC and ETEC, and 6% of DAEC patients had strains with SVG. 54% of EPEC patients carried pet-positive strains alone or in combination with astA; only this DEC group harboured cdt-positive isolates. All ETEC patients carried astA- or astA-aap-positive strains. astA and aap were the most common SVG in DAEC (3% and 2%) and non-DEC strains (21% and 13%). DEC carrying SVG are an important cause of moderate to severe bacterial diarrhoea in Mexican children.

Fig 1. PCR products.

Lane1, 1-kb molecular weight marker in base pairs; lane 2, negative control and lane 3, PCR products obtained with DNA of reference strains mix EAEC 042 (astA, pet) and EPEC O86:H34 (cdt), and DNA from the strain 98NK2 (SubAB)

Fig 2. (A) Prevalence of bacterial enteropathogens among 831 children with acute diarrhoea in Yucatan, Mexico. (B) Distribution of diarrheagenic Escherichia coli (DEC) groups, mixed DEC and hybrid DEC infections in 232 DEC positive-children.

ETEC: enterotoxigenic E. coli, tEPEC: typical enteropathogenic E. coli, aEPEC: atypical enteropathogenic E. coli, tEAEC: typical enteroaggregative E. coli, DAEC: diffusely adherent E. coli, mixed DEC: more than one DEC group strain in the same patient and hybrid DEC: a patient with an E. coli strain with two or more DEC defining genes.

Fig 3. Distribution of DEC groups, over a four-year period, by season according to yearly average precipitation and minimum, maximum, and average atmospheric temperature in Yucatan Mexico.

DAEC: diffusely adherent E. coli, EPEC: enteropathogenic E. coli, EAEC: enteroaggregative E. coli, ETEC: enterotoxigenic E. coli and MIXED DEC.