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

Abstract

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.

Untitled

“…Shahrani et al, [29] and Akter et al, [30] concluded that VT1 is the most prevalent than VT2. Prevalence of 51% among calves was obtained by Wang et al, [31] which was closely contact to our finding. Higher prevalence 83% among diarrheic calves was obtained by Pervez et al, [32].…”

“…Prevalence of STEC infection in human was 15% by Salmanzadeh-Ahrabi et al, [35], 2.3% by Rajendran et al, [36], 1.7% by van Duynhoven et al, [37], 7% was reported in patients with diarrhoea in Morogoro, Tanzania in 2006 by Raji et al, [38] and 56% by Matussek et al, [39]. The overall prevalence of virulence-associated gene VT1 only, VT2 only, VT1 and VT2 and eaeA were 10.7%, 20.8%, 68.5%, 3.9%, respectively as reported by Wang et al, [31]. Pervez et al, [32] reported that 10% of the isolates of calves were positive for VT1 gene while eaeA not detected.…”

Assessing the genomic relatedness and evolutionary rates of persistent verotoxigenic Escherichia coli serotypes within a closed beef herd in Canada

“…Herd characteristics and sample collection for VTEC have been described previously [39]. Briefly, 38 yearling heifers from three consecutive cohorts (10 to 16 individuals per cohort-year) from the Canadian Food Inspection Agency (CFIA)-National Centre for Animal Disease (NCAD) (Lethbridge, Alberta, Canada) Angus-Hereford cross research herd were sampled for VTEC on a monthly basis between April 2012 and March 2015.…”

“…Sporadic serotypes were defined as those isolated on two sampling dates or fewer overall. The population structure of VTEC within this herd has been characterized previously [39]. This was used to assess for possible lineage effects that may confound the GWAS by ensuring that persistent and sporadic serotypes were not stratified by lineage; thus, leading to the identification of lineage-specific rather than phenotype-specific loci.…”

“…In a previous study of VTEC prevalence within a closed beef herd, we identified several serotypes that were persistent within and across multiple cohort-years [39]. In this study, we aimed to examine the relatedness of persistent VTEC using this highly homogenous population as a baseline.…”