Date of Award
Master of Science
Dr. Brigid Lucey
Prof. Roy Sleator
1.6 BIOLOGICAL SCIENCES; Microbiology
Verotoxigenic Escherichia coli (VTEC) is a serious gastrointestinal pathogen associated with morbidity and mortality in the first world, as accentuated by the O104 VTEC outbreak in Germany in 2011. Molecular detection of Verotoxin (VT) has increased the detection of VTEC across Europe however, Ireland still has the highest incidence and isolation is still a key step in the confirmation of infection and the control and prevention of outbreaks. Currently no standard protocol exists for the detection, isolation and characterisation of non-O157 VTEC and it is feared that due to this that the prevalence of VTEC is under-reported. This body of research aims to validate a retrospective isolation method for all VTEC serotypes and to characterise the isolates found in the Cork region.
Retrospective isolation of VT positive samples (n=98) from frozen aliquots involved overnight enrichment in EntericBio broth at 37°C, followed by dual culture of enriched faeces and Immunomagnetic separation (IMS) suspension on MacConkey agar (without salt) and CHROMagar STEC. The total isolation rate was 80.6% (n=79) of which IMS attributed to 20.3% of the isolates. Of the 79 isolates recovered, 16.6% were not isolated by the VTEC-NRL. Isolates were characterised by serotyping, biochemical profiling and antibiotic susceptibility testing. The serotypes seen were O157 (35.4%), O26 (21.5%), O103 (3.8%), O111 (10.1%), O145 (8.9%) and non-groupable (20.3%). Sorbitol fermentation was evident in 51.2% of all isolates, the fermentation of rhamnose was seen in conjunction with sorbitol fermentation in O157 isolates and glucose fermentation was infrequent across the serogroups. Resistance to at least 1 antibiotic was high (44.9%) with 57.1% of all antibiotic resistant isolates being multi-resistant. Epidemiological analysis for 2013 revealed an increase in incidence seen in the 21-40 year age group, a second earlier spike in incidence in April-May and a suspected outbreak of O111 VTEC in the Cork region during the same year.
This thesis supports the hypothesis that VTEC is under-diagnosed and under reported, and also that there is a higher prevalence of antibiotic resistance in human VTEC strains than previously thought.
Ross, Shirley, "Isolation and Epidemiological Analysis of Verotoxigenic E. Coli from Patients with Acute Gastroenteritis: A Prospective Study Aiming to Reduce the Burden of Infection in the Cork Region." (2015). Masters [online].
Available at: https://sword.cit.ie/scimas/2
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