Abstract
The ability to produce enterohemolysin is regarded as a potential virulence factor for enterohemorrhagic Escherichia coli (EHEC) and is frequently associated with severe human diseases such as hemorrhagic colitis (HC) and the hemolytic uremic syndrome (HUS). The responsible toxin, which has also been termed EHEC-hemolysin (EHEC-Hly, syn. Ehx), belongs to the Repeats in Toxin (RTX)-family of pore-forming cytolysins and is characterized by the formation of incomplete turbid lysis zones on blood agar plates containing defibrinated sheep erythrocytes. Besides the expression of Shiga toxins (Stx) and the locus of enterocyte effacement (LEE), EHEC-Hly is a commonly used marker for the detection of potential pathogenic E. coli strains, although its exact role in pathogenesis is not completely understood. Based on the current knowledge of EHEC-Hly, this review describes the influence of various regulator proteins, explains the different mechanisms leading to damage of target cells, discusses the diagnostic role, and gives an insight of the prevalence and genetic evolution of the toxin.
Highlights
In early studies on the production of hemolysins in pathogenic Escherichia coli strains, Beutin et al.described that enteropathogenic E. coli demonstrated only a weak hemolytic activity when compared with extraintestinal E. coli strains [1]
We show that the enterohemolytic phenotype of E. coli O157:H7 strain EDL 933 was encoded on its large could show that the enterohemolytic phenotype of E. coli O157:H7 strain EDL 933 was encoded on its virulence plasmid pO157 and that it was not based on the presence of Ehly-1 and Ehly-2-sequences
The results demonstrated that Escherichia coli (EHEC)-hlyA was present in 31.8% of the non-O157 Shiga toxin-producing E. coli (STEC) strains, a percentage which was lower than that found, for example, in a comparable study of Cookson et al [17] where EHEC-hlyA was found in 63.8% of E. coli isolates obtained from cattle and sheep and 96% of isolates from patients with diarrhea
Summary
In early studies on the production of hemolysins in pathogenic Escherichia coli strains, Beutin et al. The authors found this weak hemolytic phenotype frequently in enteropathogenic E. coli (EPEC) strains isolated from infants with diarrhea. They introduced the term enterohemolysin [2]. Whereas the typical clear α-hemolytic zone appeared after 3 h of growth at 37 ◦ C, the “enterohemolytic” zones of enteropathogenic E. coli O26 strains appeared biphasic after overnight incubation This was characterized by a clear zone beneath and a small turbid zone around the colony, which looks like an incomplete hemolysis [2]. Production of blood agar plates, hemolytic phenotypes, and control derivative TS18/08 Δhns + hns is enterohemolytic. Carried out to uncover the genetics of EHEC-Hly production in enterohemolytic E. coli strains.
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