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

Alba Michel-Ayala,Mussaret Bano Zaidi,Magda León–Cen,Mathieu Picardeau,Sandra Patzi-Vargas,Iza Perez-Martinez,Damien Chaussabel,Teresa Estrada-Garcia

doi:10.1371/journal.pntd.0003510

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.

Highlights

Diarrhoeal illness is a major cause of mortality and morbidity among children less than 5 years of age accounting for 711,800 deaths and 1.731 billion cases, with an incidence of 2.7 diarrhoeal episodes per child per year in 2011 [1]
A group of bacteria known as diarrheagenic Escherichia coli (DEC) have been recognized as a major cause of diarrheal illness worldwide
Our results strongly suggest that diarrheagenic Escherichia coli groups (DEC) carrying supplementary virulence genes (SVG) are an important cause of moderate to severe bacterial diarrhoeal disease in Mexico

Summary

Introduction

Diarrhoeal illness is a major cause of mortality and morbidity among children less than 5 years of age accounting for 711,800 deaths and 1.731 billion cases, with an incidence of 2.7 diarrhoeal episodes per child per year in 2011 [1]. In Mexico, diarrhoeal illness continues to be a national health problem [2,3]. It is the second cause of morbidity and the fifth cause of mortality among children under five years of age. DEC infections have been associated with acute and persistent diarrhoea (>14 days), as well as with growth delays and stunting, which in turn can lead to long-term cognitive impairment [15,16,17]. Several studies suggest that DEC is responsible for up to 30%-40% of acute diarrhoeal episodes in children [18]

Methods

Results

Discussion

Conclusion