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

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

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

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

Seasonal^z proportions of fecal samples yielding isolates of Top 7 serogroups^y.

<p>Bars indicate 95% confidence intervals. Means within a serogroup with different superscripts, differ (<i>P</i> < 0.001). ^zSeason: spring (March, April, May), summer (June, July, August), fall (September, October, November), winter (December, January, February). ^yIf 25 isolates were collected from a serogroup over a minimum of 2 samplings in a season, IMS was discontinued for subsequent samplings until the following season.</p

Seasonal prevalence (%) of the most frequent combinations of Top 7 serogroups detected by PCR from pooled samples of cattle feces collected at delivery to slaughter (n = 1,749).

<p>Seasonal prevalence (%) of the most frequent combinations of Top 7 serogroups detected by PCR from pooled samples of cattle feces collected at delivery to slaughter (n = 1,749).</p

Prevalence of Shiga-toxin genes in isolates of the Top Seven serogroups according to zone of cattle origin and serogroup.

<p>Prevalence of Shiga-toxin genes in isolates of the Top Seven serogroups according to zone of cattle origin and serogroup.</p

Overall proportions of pooled fecal samples (n = 1749) positive for Top 7 serogroups by PCR, isolates collected after immunomagnetic separation (IMS) and virulence genes in isolates.

<p>Adjusted means are reported.</p

Seasonal^z PCR detection of Top Seven serogroups in feces of western Canadian slaughter cattle.

<p>Bars indicate 95% confidence intervals. Means within a serogroup with different superscripts differ (<i>P</i> < 0.001). ^zSeason: spring (March, April, May), summer (June, July, August), fall (September, October, November), winter (December, January, February).</p

Table_10_Multi-Year Persistence of Verotoxigenic Escherichia coli (VTEC) in a Closed Canadian Beef Herd: A Cohort Study.DOCX

In this study, fecal samples were collected from a closed beef herd in Alberta, Canada from 2012 to 2015. To limit serotype bias, which was observed in enrichment broth cultures, Verotoxigenic Escherichia coli (VTEC) were isolated directly from samples using a hydrophobic grid-membrane filter verotoxin immunoblot assay. Overall VTEC isolation rates were similar for three different cohorts of yearling heifers on both an annual (68.5 to 71.8%) and seasonal basis (67.3 to 76.0%). Across all three cohorts, O139:H19 (37.1% of VTEC-positive samples), O22:H8 (15.8%) and O?(O108):H8 (15.4%) were among the most prevalent serotypes. However, isolation rates for serotypes O139:H19, O130:H38, O6:H34, O91:H21, and O113:H21 differed significantly between cohort-years, as did isolation rates for some serotypes within a single heifer cohort. There was a high level of VTEC serotype diversity with an average of 4.3 serotypes isolated per heifer and 65.8% of the heifers classified as “persistent shedders” of VTEC based on the criteria of >50% of samples positive and ≥4 consecutive samples positive. Only 26.8% (90/336) of the VTEC isolates from yearling heifers belonged to the human disease-associated seropathotypes A (O157:H7), B (O26:H11, O111:NM), and C (O22:H8, O91:H21, O113:H21, O137:H41, O2:H6). Conversely, seropathotypes B (O26:NM, O111:NM) and C (O91:H21, O2:H29) strains were dominant (76.0%, 19/25) among VTEC isolates from month-old calves from this herd. Among VTEC from heifers, carriage rates of vt1, vt2, vt1+vt2, eae, and hlyA were 10.7, 20.8, 68.5, 3.9, and 88.7%, respectively. The adhesin gene saa was present in 82.7% of heifer strains but absent from all of 13 eae+ve strains (from serotypes/intimin types O157:H7/γ1, O26:H11/β1, O111:NM/θ, O84:H2/ζ, and O182:H25/ζ). Phylogenetic relationships inferred from wgMLST and pan genome-derived core SNP analysis showed that strains clustered by phylotype and serotype. Further, VTEC strains of the same serotype usually shared the same suite of antibiotic resistance and virulence genes, suggesting the circulation of dominant clones within this distinct herd. This study provides insight into the diverse and dynamic nature of VTEC populations within groups of cattle and points to a broad spectrum of human health risks associated with these E. coli strains.</p