Analysis of the virulence of an atypical enteropathogenic Escherichia coli strain in vitro and in vivo and the influence of type three secretion system.

Suely C F Sampaio,Mônica A M Vieira,Ivan H J Koh,Ana M A Liberatore,Fabiana C Moreira,Claudete S A Ferreira,Antônio P Ferreira,Terezinha Knobl,Fabiano T Romão,Rodrigo T Hernandes,Rita Sinigaglia-Coimbra,Tania A T Gomes,Aloísio Felipe-Silva

doi:10.1155/2014/797508

Abstract

Atypical enteropathogenic Escherichia coli (aEPEC) inject various effectors into intestinal cells through a type three secretion system (T3SS), causing attaching and effacing (A/E) lesions. We investigated the role of T3SS in the ability of the aEPEC 1711-4 strain to interact with enterocytes in vitro (Caco-2 cells) and in vivo (rabbit ileal loops) and to translocate the rat intestinal mucosa in vivo. A T3SS isogenic mutant strain was constructed, which showed marked reduction in the ability to associate and invade but not to persist inside Caco-2 cells. After rabbit infection, only aEPEC 1711-4 was detected inside enterocytes at 8 and 24 hours pointing to a T3SS-dependent invasive potential in vivo. In contrast to aEPEC 1711-4, the T3SS-deficient strain no longer produced A/E lesions or induced macrophage infiltration. We also demonstrated that the ability of aEPEC 1711-4 to translocate through mesenteric lymph nodes to spleen and liver in a rat model depends on a functional T3SS, since a decreased number of T3SS mutant bacteria were recovered from extraintestinal sites. These findings indicate that the full virulence potential of aEPEC 1711-4 depends on a functional T3SS, which contributes to efficient adhesion/invasion in vitro and in vivo and to bacterial translocation to extraintestinal sites.

Highlights

Atypical enteropathogenic Escherichia coli are emerging agents of diarrhea
We showed that Atypical enteropathogenic Escherichia coli (aEPEC) 1711-4 infected-animals had intestinal mesenteric microcirculation injury and systemic hypoperfusion similar to those observed with the virulent murine E. coli strain R6 [17, 18]
Our results demonstrated that the 1711-4 escN mutant was unable to cause A/E lesion in HeLa cells and to adhere effectively to Caco-2 cells indicating that T3SS contributes to aEPEC 1711-4 adhesion

Summary

Introduction

Atypical enteropathogenic Escherichia coli (aEPEC) are emerging agents of diarrhea. They differ from typical EPEC (tEPEC) strains mainly by the absence of the EAF (EPEC adherence factor) plasmid [1, 2]. Like tEPEC, aEPEC strains inject various effector proteins into enterocytes through a type three secretion system (T3SS) leading to the formation of attaching-effacing (A/E) lesions [3,4,5]. Many other T3SSdependent effector proteins, such as Map (mitochondrialassociated protein) and EspF, have important roles in aEPEC pathogenesis. These proteins have redundant functions and can cause epithelial barrier disruption by interacting with tight junctions, leading to cell death by apoptosis [9, 10]

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