Mechanisms involved in the adaptation of Escherichia coli O157:H7 to the host intestinal microenvironment.

Romina J Fernandez-Brando,Marina S Palermo,M Victoria Ramos,Jai Tree,Johanna Montañez-Culma,Gonzalo E Pineda,Sean P Mcateer,Yennifer Cortés-Araya,Stephen Fitzgerald,Alan Bernal,David L Gally,Federico Fuentes

doi:10.1042/cs20200971

Abstract

Host adaptation of pathogens may increase intra- and interspecies transmission. We showed previously that the passage of a clinically isolated enterohemorrhagic Escherichia coli (EHEC) O157 strain (125/99) through the gastrointestinal tract of mice increases its pathogenicity in the same host. In this work, we aimed to elucidate the underlying mechanism(s) involved in the patho-adaptation of the stool-recovered (125RR) strain. We assessed the global transcription profile by microarray and found almost 100 differentially expressed genes in 125RR strain compared with 125/99 strain. We detected an overexpression of Type Three Secretion System (TTSS) proteins at the mRNA and protein levels and demonstrated increased adhesion to epithelial cell lines for the 125RR strain. Additional key attributes of the 125RR strain were: increased motility on semisolid agar, which correlated with an increased fliC mRNA level; reduced Stx2 production at the mRNA and protein levels; increased survival at pH 2.5, as determined by acid resistance assays. We tested whether the overexpression of the LEE-encoded regulator (ler) in trans in the 125/99 strain could recreate the increased pathogenicity observed in the 125RR strain. As anticipated ler overexpression led to increased expression of TTSS proteins and bacterial adhesion to epithelial cells in vitro but also increased mortality and intestinal colonization in vivo. We conclude that this host-adaptation process required changes in several mechanisms that improved EHEC O157 fitness in the new host. The research highlights some of the bacterial mechanisms required for horizontal transmission of these zoonotic pathogens between their animal and human populations.

Highlights

Enterohemorrhagic Shiga toxin (Stx)-producing Escherichia coli (EHEC) O157:H7 has been recognized as the most frequent serotype associated with large outbreaks or sporadic cases of hemorrhagic colitis and hemolytic uremic syndrome (HUS) in many countries [1]
To understand the differences that could explain the increased pathogenicity observed in the stool-recovered (125RR) strain we carried out a global analysis of gene expression by using high-throughput DNA microarrays
We have investigated mechanisms by which an EHEC O157 strain subject to repeated passage through the mouse intestinal tract has increased pathogenesis

Summary

Introduction

Enterohemorrhagic Shiga toxin (Stx)-producing Escherichia coli (EHEC) O157:H7 has been recognized as the most frequent serotype associated with large outbreaks or sporadic cases of hemorrhagic colitis and hemolytic uremic syndrome (HUS) in many countries [1]. The production of Stx determines HUS onset, factors that modulate intestinal colonization are key components in pathogenesis and host mucosal immune response. The locus of enterocyte effacement (LEE) encodes structural and effector proteins of the TTSS, which is an important virulence factor [5]. The TTSS as well as numerous non-LEE-encoded effector proteins are involved in the colonization process, and allow the modulation of host-cell signaling to favor bacterial replication and survival. Recent work highlights the importance of Stx for EHEC O157 colonization of cattle [6]. All these virulence factors may contribute to the establishment of infection and subsequent pathology in exposed humans. Virulence gene expression in EHEC is regulated by a number of environmental factors including temperature, culture medium and host-cell factors [7]

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