Regulation of pathogenicity island and plasmid borne virulence determinants of Escherichia coli 0157

Abstract

The human intestinal pathogen Escherichia coli 0157 is the most common serotype of an important group of zoonotic pathogens known as enterohaemorrhagic E. coli (EHEC). E. coli 0157 are ubiquitous in the environment, yet human disease incidence due to the organism is relatively low. This study has shown that E. coli 0157 strains from cattle and humans are phenotypically heterogeneous, and differ in their ability to secrete effector proteins from the locus of enterocyte effacement type III secretion system. A subset ofstrains secrete high levels ofthe'LEE4 protein EspD, with strains isolated from human disease cases tending to be high secretors (p<0.001) and secrete, on average, 90-fold higher levels ofthe EspD protein than strains isolated from asymptomatic cattle. This indicates that potentially only a subset of strains present in the bovine population may be a serious threat to human health. This study has also sought to elucidate the regulation of expression of two genes present on the large plasmid pO157, namely toxB and espP through the use of chromosomally-integrated translational fusions to both p-galactosidase and enhanced green fluorescent protein. From the data presented it is proposed that espP expression is multifactorial and appears to involve several E. coli 0157 regulatory factors some of which appear specific to E. coli 0157. EspP is not involved in adhesion of E. coli 0157 to eukaryotic cells, or in A/E lesion formation, but perhaps plays a role in the intestinal environment before attachment. toxB is involved in type III secretion of LEE proteins, and its expression in EHEC 0157 appears to be tightly controlled by a factor present on the LEE pathogenicity island.