Verocytotoxin-producing Escherichia coli (VTEC) are important human pathogens that may cause diarrhoea, haemorrhagic colitis and haemolytic uremic syndrome (HUS). Worldwide, non-sorbitol-fermenting (NSF) VTEC O157:H7 is the most common serogroup associated with HUS but several non-O157:H7 serogroups have emerged as causes of this disease. This research investigated the pathogenic potential of two non-O157:H7 serogroups: O26 and sorbitol-fermenting (SF) O157:NM. While VTEC O26 have emerged as a significant cause of HUS in continental Europe, human infections associated with this pathogen are uncommon in Scotland and generally only result in simple diarrhoea. The study characterised E. coli O26 isolates recovered from human infections in Europe and Scotland and isolates collected from Scottish cattle with the objectives to identify factors which may allow strains to cause more serious clinical disease and to investigate the potential of bovine VTEC O26 in Scotland to cause human infection. MLST analysis of housekeeping genes found little genetic variation in the genomic ‘backbone’ among the vast majority of E. coli O26 isolates. The gene for verocytotoxin 2 (vtx2) alone was carried by VTEC O26 isolates recovered from patients in continental Europe but was found in no Scottish human isolate, where the majority of isolates did not harbour a vtx gene. It was demonstrated that among the European VTEC O26 human isolates, 67% carried a specific allele within the promoter region for LEE1 and 87% harboured the tccP2 gene. In contrast, no Scottish VTEC O26 human isolate carried this allele or the tccP2 gene. The impact these genotypic characteristics have on the pathogenic potential of a strain remains uncertain. There were no clear differences in verocytotoxin titres, levels of LEEencoded protein secretion or levels of adherence to Caco-2 cells between VTEC O26 isolates recovered from human infections of varying severity. However, levels of LEE-encoded protein secretion from cattle isolates were generally higher than those from many of the human isolates. The differences in pathogenic potential between isolates are likely to be due to horizontally acquired DNA, including vtx2 carriage and the O-island-phage-associated effector protein repertoire. Further work is required to determine if the differences identified may also impact on shedding levels from cattle and therefore the likelihood of transmission to humans. Since 1988, SF VTEC O157:NM strains have emerged and have been associated with a higher incidence of progression to HUS than NSF VTEC O157:H7. This study investigated bacterial factors that may account for the increased pathogenic potential of SF VTEC O157:NM. While no evidence of toxin or toxin expression differences between the two VTEC O157 groups was found, the SF VTEC O157:NM strains adhered at significantly higher levels to a human colonic cell line. Under the conditions tested, curli were shown to be the main factor responsible for the increased adherence to Caco-2 cells. The capacity of SF VTEC O157:NM strains to express curli at 37C may have relevance to the epidemiology of human infections as curliated strains could promote higher levels of colonization and inflammation in the human intestine. In turn this could lead to increased toxin exposure and an increased likelihood of progression to HUS.

<p>Escherichia coli is a natural inhabitant of the intestines of both humans and animals, but there are also several pathogenic types of E. coli which cause disease in humans.</p><p>Strains of enterohemorrhagic E. coli (EHEC) have been associated with outbreaks of diarrhea, hemorrhagic colitis and hemolytic uremic syndrome in humans. Most clinical signs of disease arise as a consequence of the production of shigatoxin 1 and 2 or combination of these toxins. Other major virulence factors include EHEC hemolysin and intimin, the product of the eae gene that is involved in attaching and effacing adherence phenotype. EHEC has also been associated with uncomplicated diarrhea.</p><p>The capacity to control EHEC disease and to limit the scale of outbreaks is dependent upon prompt diagnosis and identification of the source of infection.</p><p>The principal reservoirs of EHEC are cattle and food products, which presumably have come into contact with domestic animal manure and/or are inadequately pasteurised, these are important vehicles of infection.</p><p>In the present study, the PCR technique with primers detecting the verocytotoxin genes was shown to be a possible method to screen for and identify EHEC.</p><p>In summary stx genes were detected in 16 samples of 228 sampels and the eae gene was detected in 2 samples using PCR.</p>

Escherichia coli is a natural inhabitant of the intestines of both humans and animals, but there are also several pathogenic types of E. coli which cause disease in humans. Strains of enterohemorrhagic E. coli (EHEC) have been associated with outbreaks of diarrhea, hemorrhagic colitis and hemolytic uremic syndrome in humans. Most clinical signs of disease arise as a consequence of the production of shigatoxin 1 and 2 or combination of these toxins. Other major virulence factors include EHEC hemolysin and intimin, the product of the eae gene that is involved in attaching and effacing adherence phenotype. EHEC has also been associated with uncomplicated diarrhea. The capacity to control EHEC disease and to limit the scale of outbreaks is dependent upon prompt diagnosis and identification of the source of infection. The principal reservoirs of EHEC are cattle and food products, which presumably have come into contact with domestic animal manure and/or are inadequately pasteurised, these are important vehicles of infection. In the present study, the PCR technique with primers detecting the verocytotoxin genes was shown to be a possible method to screen for and identify EHEC. In summary stx genes were detected in 16 samples of 228 sampels and the eae gene was detected in 2 samples using PCR.

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