Total number of generic <i>E</i>. <i>coli</i> (GEC), O178, O157, shiga toxin (<i>stx</i>) 1 and 2 specific gene fragments in samples from slaughterhouse A or B (calculated using droplet digital PCR).

In each comparison between slaughterhouse A and B there were significant differences in enumeration of gene fragments, denoted by symbol α. Note: *The red line is the average number of GEC, O178, O157, stx1 and stx2 at each slaughterhouse and the black line in the boxes is the median.</p

Percentage of conventional PCR <i>Escherichia coli</i> O178 positives by season and slaughterhouse from 1,773 enrichments.

Percentage of conventional PCR Escherichia coli O178 positives by season and slaughterhouse from 1,773 enrichments.</p

Proportion of O157, O178, shiga toxin (<i>stx</i>) 1 and shiga toxin 2 specific gene fragments in samples for A and B slaughterhouses calculated using droplet digital PCR enumerations and comparison of the average proportion of the target gene compared to generic <i>Escherichia coli</i> (GEC) in the samples.

Note: *Proportions are based on the total E. coli counts. **Red line is the average proportion for the group and black line in the boxes is the median. *** Symbol: α denotes a significant difference between O157 at site A and B and between the average proportion of O178 and O157 (P < 0.05).</p

Total number of shiga toxin (<i>stx</i>) 1 and 2 specific gene fragments versus reduced O157 enumerations (-23% for non-STEC O157) for summer and winter across the sampling period.

<p>Each peak denotes a sample and the color (red = O157, blue = <i>stx</i>₁ and green = <i>stx</i>₂) indicates the target.</p

Mean and minimum temperatures (°C) for a location equidistant from the slaughter plants^z between June 1, 2013 and May 31, 2015.

Ambient temperature (°C).</p

Primer sequence and amplicon size for O178 conventional PCR screening and for Evagreen droplet digital PCR assays.

<p>Primer sequence and amplicon size for O178 conventional PCR screening and for Evagreen droplet digital PCR assays.</p

Zones of cattle origin and numbers of samples collected per zone.

Zone 1 (n = 1012), fescue grassland; Zone 2 (n = 262), mixed grassland; Zone 3 (n = 316), aspen parkland; Zone 4 (n = 159), Saskatchewan. Reprinted from www.nrcan.gc.ca/earth-sciences/geography/atlas-canada/reference-maps/16846#provincial-and-territorial under a CC BY license, with permission from Natural Resources Canada, original copyright [2004].</p

Influence of Season and Feedlot Location on Prevalence and Virulence Factors of Seven Serogroups of <i>Escherichia coli</i> in Feces of Western-Canadian Slaughter Cattle

<div><p>Pooled feces collected over two years from 1749 transport trailers hauling western-Canadian slaughter cattle were analysed by PCR for detection of <i>Escherichia</i> coli serogroups O26, O45, O103, O111, O121, O145, and O157. Sequential immunomagnetic separation was then used to collect bacterial isolates (n = 1035) from feces positive for target serogroups. Isolated bacteria were tested by PCR to confirm serogroup and the presence of <i>eae</i>, <i>ehxA</i>, <i>stx</i>_<i>1</i>, and <i>stx</i>_<i>2</i> virulence genes. Based on PCR screening, serogroup prevalence in feces ranged from 7.0% (O145) to 94.4% (O103) with at least 3 serogroups present in 79.5% of samples. Origin of cattle affected serogroup PCR prevalence and O157 was most prevalent in feces from south-west Alberta (<i>P</i> < 0.001). All serogroups demonstrated seasonal variations in PCR prevalence, with O26, O45, O103, O121, and O157 least prevalent (<i>P</i> < 0.001) in cooler winter months, while uncommon serogroups O111 and O145 increased in prevalence during winter (<i>P</i> < 0.001). However, isolates collected during winter were predominantly from serogroups O103 and O45. No seasonal variation was noted in proportion of isolates which were Shiga toxin containing <i>E</i>. <i>coli</i> (STEC; <i>P</i> = 0.18) or positive for Shiga toxin and <i>eae</i> (enterohemorrhagic <i>E</i>. <i>coli</i>; EHEC; <i>P</i> = 0.29). Isolates of serogroups O111, O145, and O157 were more frequently EHEC than were others, although 37.6–54.3% of isolates from other serogroups were also EHEC. Shiga-toxin genes present also varied by geographic origin of cattle (<i>P</i> < 0.05) in all serogroups except O157. As cattle within feedlots are sourced from multiple regions, locational differences in serogroup prevalence and virulence genes imply existence of selection pressures for <i>E</i>. <i>coli</i> and their virulence in western-Canadian cattle. Factors which reduce carriage or expression of virulence genes, particularly in non-O157 serogroups, should be investigated.</p></div

Comparison of the average proportion for O178, O157, shiga toxin (<i>stx</i>) 1 and 2 for the two sampling sites, A and B for each season based on the total generic <i>E</i>. <i>coli</i> count.

<p>Note: * Symbol: α above specific gene fragment denotes a significant difference in enumerations between summer and winter for that target (<i>P</i> < 0.05).</p

Influence of geographical origin of cattle on frequency of PCR positives for Top 7 serogroups in pooled fecal samples.

<p>Influence of geographical origin of cattle on frequency of PCR positives for Top 7 serogroups in pooled fecal samples.</p