New approaches to culture and detection of verocytotoxin producing escherichia coli (VTEC) in clinical laboratory diagnosis

Abstract

VTEC of serogroups other than 0157 have not been studied widely in the UK. These organisms are difficult to isolate and few laboratories investigate faecal specimens for their presence. Due to this the true prevalence and significance of these
organisms is unknown. This study describes an investigation of the growth of non-0157 VTEC in enrichment culture using indirect conductimetry. The media developed for enrichment culture of 0157 VTEC was found to be inappropriate for enrichment culture of some non-0157 VTEC strains. This was particularly evident among members of serogroups 026 and 0111 that are considered to be the most clinically relevant after 0157. Based on these finding an alternative medium, GN broth was recommended for enrichment culture ofnon-0l57 VTEC.
Non-0157 VTEC cannot be distinguished from non-pathogenic E.coli using solid, differential plate media and it was necessary to use other methods to detect these organisms in enrichment cultures. A sensitive, single target, Polymerase Chain Reaction (PCR) was identified that was able to detect the verocytotoxin (VT) genes produced by VTEC. This PCR was used in conjunction with an internal control and a novel density gradient centrifligation, pre-PCR sample preparation procedure, to detect VTEC in faeces.
A prospective investigation of faeeal specimens collected from cases of gastrointestinal disease in the North West of England was undertaken using the developed methods. Evidence of VTEC was found in 1.6-2.6% of the specimens tested
and this detection rate was found to be similar to those of other European countries and the USA. VTEC could not be isolated from any of the specimens investigated however the presence of Veroeytotoxin was verified using the Vero cell assay.
It was concluded that non-0157 VTEC could potentially be a significant cause of gastrointestinal disease in the North West of England and that further studies are required to clarify the role of these organisms in the aetiology of gastrointestinal
disease.