Description of a Novel Intimin Variant (Type ζ) in the Bovine O84:NM Verotoxin-Producing Escherichia coli Strain 537/89 and the Diagnostic Value of Intimin Typing

Abstract

Infections with verotoxin-producing Escherichia coli (VTEC) has resulted in increasing numbers of human illnesses annually. These illnesses usually result from the ability of VTEC to cause the attaching and effacing lesions (AE lesion). The AE phenotype is encoded by the locus of enterocyte effacement (LEE) pathogenicity island. A key adhesion factor involved is the outer membrane protein intimin, encoded by the eae gene within the LEE. Intimin types α, β, γ, δ, and ε have been described previously. Each intimin represents distinct phylogenetic lineages of LEE-positive strains. A new intimin type ζ was identified in a VTEC strain of the serotype O84:NM (nonmotile) that was isolated from a calf with diarrhea. ζ intimin showed the highest similarity (88%) of its amino acid sequence to the α intimin. For diagnostic purposes, we established a polymerase chain reaction (PCR) method for diagnosis of the key virulence traits of VTEC (i.e., verotoxins and intimins). This method also distinguishes between the toxins (VT1 and VT2) and the six intimin types. By applying the PCR method, intimin ζ in strains of other VTEC serotypes O84:H2, O92:NM, O119:H25, and O150:NM was identified. Because the intimin types represent distinctive phylogenetic E. coli lineages, application of the intimin subtyping PCR offers significant benefits. These include improving diagnosis of VTEC infection and increasing the understanding of evolution of attaching and effacing VTEC and other LEE-positive bacteria.