Atypical enteropathogenic Escherichia coli strains form biofilm on abiotic surfaces regardless of their adherence pattern on cultured epithelial cells.

Hebert F Culler,Cecilia M Abe,Cristiane M Mota,Waldir P Elias,Marcelo P Sircili,Marcia R Franzolin

doi:10.1155/2014/845147

Abstract

The aim of this study was to determine the capacity of biofilm formation of atypical enteropathogenic Escherichia coli (aEPEC) strains on abiotic and biotic surfaces. Ninety-one aEPEC strains, isolated from feces of children with diarrhea, were analyzed by the crystal violet (CV) assay on an abiotic surface after 24 h of incubation. aEPEC strains representing each HEp-2 cell type of adherence were analyzed after 24 h and 6, 12, and 18 days of incubation at 37°C on abiotic and cell surfaces by CFU/cm2 counting and confocal laser scanning microscopy (CLSM). Biofilm formation on abiotic surfaces occurred in 55 (60.4%) of the aEPEC strains. There was no significant difference in biofilm biomass formation on an abiotic versus prefixed cell surface. The biofilms could be visualized by CLSM at various developmental stages. aEPEC strains are able to form biofilm on an abiotic surface with no association with their adherence pattern on HEp-2 cells with the exception of the strains expressing UND (undetermined adherence). This study revealed the capacity of adhesion and biofilm formation by aEPEC strains on abiotic and biotic surfaces, possibly playing a role in pathogenesis, mainly in cases of persistent diarrhea.

Highlights

Enteropathogenic Escherichia coli (EPEC) is a major cause of diarrhea in children in developing countries [1, 2]
Adherence assays performed with cultured epithelial cells (HeLa or HEp-2 cell lines) show that atypical EPEC (aEPEC) strains often express a defined pattern known as localized-like adherence (LAL) characterized by loose clusters of bacteria adhered to the cell surface
Other adherence patterns can be found in aEPEC: diffuse adherence (DA), where the bacteria adhere diffusely to the cell surface; aggregative adherence (AA), where the bacteria adhere to the cell surface and to the coverslip in a stacked brick pattern; localized adherence (LA6h), where the bacteria adhere to the cell surface as tight clusters; and undetermined adherence (UND), when bacterial adherence cannot be classified in one of these defined patterns [6]

Summary

Introduction

Enteropathogenic Escherichia coli (EPEC) is a major cause of diarrhea in children in developing countries [1, 2]. AEPEC is defined as E. coli strains that lack the EAF plasmid (pEAF) and Shiga toxinencoding genes (stx) do not express the bundle-forming pilus (BFP) and produce the characteristic histopathology lesion known as attaching and effacing (A/E) on intestinal mucosa [3,4,5,6]. The A/E lesion results from intimate bacterial adherence to the enterocytes, local microvillus effacement, and accumulation of polymerized actin of the cytoskeleton underneath adherent bacteria forming pedestal-like structures [7]. Adherence assays performed with cultured epithelial cells (HeLa or HEp-2 cell lines) show that aEPEC strains often express a defined pattern known as localized-like adherence (LAL) characterized by loose clusters of bacteria adhered to the cell surface. Nonadherent aEPEC strains are reported less often [5, 8,9,10]

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