A sensitive method for the recovery of Escherichia coli serogroup O55 including Shiga toxin-producing variants for potential use in outbreaks.

ABSTRACT

AIM: Shiga toxin-producing Escherichia coli (STEC) cause bloody diarrhoea, kidney failure and occasionally death. However, identifying the source of infection caused by STEC other than serogroup O157 is hampered by the availability of sensitive methods for detecting these pathogens. In this study, we developed novel tools for detecting E. coli O55 that is potentially associated with human outbreaks. METHODS AND RESULTS: Overall specificity of immuno-magnetic separation (IMS) beads coated with anti-O55 serum was good with exception of cross-reactivity with E. coli O22 and O23, which was eliminated using an O55-specific PCR. Limit of detection for E. coli O55 using O55-IMS beads in spiked cattle faeces was on average 50 CFU per ml (range 1-90), and improved to <10 CFU per ml using the O55-specific PCR, following IMS on samples enriched for 2 h with E. coli O55. Application of these tools to test cattle faeces collected on-farm allowed the isolation of O55H19, which through whole genome sequencing was compared to STEC O55H7 human outbreak strains. CONCLUSION: These tools provide a sensitive method which could be used to screen samples for STEC O55, whether environmental or human clinical. SIGNIFICANCE AND IMPACT OF THE STUDY Several human outbreaks reported in England were caused by STEC O55H7. Tools developed here could assist in identification of the environmental source for these isolates, which has not yet been established.