• Mellor, Glen
• Barlow, Robert
• Delannoy, Sabine
• Duffy, Lesley
• Fegan, Narelle
• Fach, Patrick

Abstract

Introduction: Testing of beef products for the presence of pathogenic Shiga toxin-producing E. coli (pSTEC) occurs in a number of international markets. Testing typically relies on the molecular detection of stx, eae, and a pSTEC O serotype in mixed bacterial enrichments. Refinement of pSTEC test systems is occurring via the incorporation of additional gene targets but remains complicated by the presence of non-pSTEC isolates such as aEPEC that may harbor various combinations of these target genes. The purpose of this work was to conduct comparative genome assessment of a collection of aEPEC isolates from Australian cattle to identify the impact these organisms may have on pSTEC detection and confirmation test systems. Methods: Twenty-five aEPEC isolates comprising O26, O103, O145 and non-pSTEC serotypes from Australian cattle were characterized for the presence of 50 genetic targets including non-LEE effector genes, CRISPR sequences, T3SS encoding genes and the E. coli attaching and effacing gene-positive conserved fragment 1 (ecf1) using the Biomark Fluidigm 48.48 Dynamic Array and conventional PCR. Results: Two distinct populations of aEPEC isolates were identified based on the presence of ecf1. Isolates harboring ecf1 were likely to contain additional pSTEC markers espK (73%), espV (93%), espN (67%), Z2098 (87%), Z2099 (87%) and ureD (80%). In contrast ecf1 negative isolates did not harbor any of these markers. With the exception of a single ecf1 negative O26 isolate, the presence of CRISPR sequences was exclusively associated with ecf1 positive isolates of pSTEC serotypes.Significance:Whilst the clinical importance of aEPEC strains that harbor a range of additional pSTEC markers is not well understood, their presence in Australian cattle populations is problematic for pSTEC test system performance. Identification of additional gene markers or SNPs to distinguish aEPEC strains from pSTEC would substantially enhance the power of pSTEC test systems.

Topics

• impedance spectroscopy