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

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

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 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