The recovery of O55 E. coli from faeces including Verocytotoxin producing variants. The recovery of O55 E. coli from faeces including Verocytotoxin producing variants

Verocytotoxigenic E. coli (VTEC) is the cause of severe human illness throughout the world. Infection is often the result of the consumption of contaminated food and water or via close contact with animal faeces. Between 2014 and 2015 a number of individuals within a small region of England became infected with VTEC of serogroup O55:H7. Extensive environmental sampling failed to identify the source of the outbreak. The aim of this work was to develop and validate novel tools for the isolation and detection of O55 E. coli, which could be applied to any future outbreaks. Magnetic beads coated with anti-O55 serum were prepared and tested for specificity against a panel of 156 different E. coli serotypes. Overall specificity of the beads was good with the expectation of E. coli O22 and O23, which are known to cross-react with O55 anti-sera. The sensitivity of the O55-beads for the isolation of E. coli O55 was tested in spiking studies with cattle faeces. The limit of detection for IMS-beads in spiked faeces was on average 50 CFU/ml. Enrichment step did not improve the sensitivity of IMS-culture. However, the introduction of an IMS-PCR step, to detect the O55 wzy gene, following IMS, improved the detection sensitivity to <10 CFU/ml. Application of these tools to cattle faeces allowed the detection and isolation of an O55:H19 strain. In the future, these tools could be utilised in an outbreak to test faeces and environmental samples to assist in the identification of cases and source.