Variable Efﬁcacy of a Vaccine and Direct-Fed Microbial
for Controlling Escherichia coli O157:H7
in Feces and on Hides of Feedlot Cattle
Calvin W. Booker,
and G. Kee Jim
To evaluate the efﬁcacy of a type-III secreted proteins vaccine and a Lactobacillus-acidophilus–based direct-
fed microbial (DFM) for controlling Escherichia coli O157:H7, cattle (n=864) were allocated to the following
groups: DFM, ﬁnishing diets containing 10
colony-forming units (CFU)/animal/day L. acidophilus and Pro-
pionibacterium freudenreichii; VAC, ﬁnishing diets and 2 mL intramuscular injection of vaccine at allocation
and 28 days later; or CON, ﬁnishing diets only. Cattle within replicates were stratiﬁed by initial levels of E. coli
O157:H7 and randomized to experimental groups, with 30 pens allocated on June 15, 2011 (AS1), 18 pens
allocated on June 28, 2011 (AS2), and 18 cattle per pen. Rectal fecal samples and perineal swabs were collected
at 28-day intervals until shipment to slaughter (103–145 days on trial). Numbers of cattle with enumerable
E. coli O157:H7 ( ‡1.6 CFU/g feces) were reduced in AS1 and AS2 by VAC ( p=0.008), although interventions
had no impact on numbers of E. coli O157:H7 shed. For AS1, VAC reduced prevalence of E. coli O157:H7 in
feces ( p=0.03) and perineal swabs ( p=0.04) in the feeding period but not at shipment to slaughter. For AS2,
prevalence of E. coli O157:H7 was not reduced in either feces or perineal swabs by VAC at any time. For AS1,
DFM reduced prevalence of E. coli O157:H7 in perineal swabs ( p=0.01) during the feeding period. For AS2,
DFM increased E. coli O157:H7 detection in feces ( p=0.03) and perineal swabs ( p=0.01) at shipment to
slaughter. Seventy-ﬁve percent of AS1 E. coli O157:H7 isolates had only stx1, while 87% of AS2 isolates had
stx1 and stx2 genes. Of the two interventions, VAC shows the most potential for pre-harvest control of E. coli
O157:H7, but due to variable efﬁcacy of both DFM and VAC, additional product development is necessary to
ensure more consistent pre-harvest control of E. coli O157:H7.
Cattle are known E. coli O157:H7 reservoirs, and on-
farm methods investigated have included Lactobacillus
acidophilus–based direct-fed microbials (DFM) (Brashears
et al., 2003; Younts-Dahl et al., 2005; Peterson et al., 2007a;
Cull et al., 2012) and vaccines against type III secreted
proteins (Potter et al., 2004; Peterson et al., 2007b; Moxley
et al., 2009) or siderophore receptor and porin proteins
(Thomson et al., 2009; Fox et al., 2009; Cull et al., 2012).
Ideal on-farm methods would control this zoonotic pathogen
in feces to reduce environmental contamination (Berger
et al., 2010), on hides at slaughter to potentially reduce
contamination of beef products (Elder et al., 2000), and have
relatively long durations of control (feedlot entry to slaugh-
ter). Vaccination for on-farm control of E. coli O157:H7 has
recently been reviewed (Snedeker et al., 2012; Varela et al.,
2012; Matthews et al., 2013), but studies comparing vaccines
and DFM are rare. Accordingly, the objective of this study
was to compare the efﬁcacy of a DFM to two doses of a type
III secreted-proteins vaccine for controlling E. coli O157:H7
in western-Canadian feedlot cattle over a complete feeding
Materials and Methods
Facilities and feed
The project was conducted in a small pen research facility
( June–November 2011), using cattle housed in open air, dirt-
ﬂoor pens with central feed alleys and porosity fencing. Feed
and water were available ad libitum. Diets were standardized
within replicate and included approximately 92% barley
grain, 5% forage, 2% supplement, and 1% corn dried distiller
grains (cDDG) on a dry-matter basis to meet beef cattle
Alberta Agriculture and Rural Development, Agriculture Centre, Lethbridge, Alberta, Canada.
Feedlot Health Management Services Ltd., Okotoks, Alberta, Canada.
FOODBORNE PATHOGENS AND DISEASE
Volume 11, Number 5, 2014
ªMary Ann Liebert, Inc.
nutrient requirements (NRC, 2000). Diets were blended in
truck-mounted mixer boxes equipped with electronic load
cells, and contained monensin (Elanco Animal Health,
Guelph, ON), tylosin (Elanco Animal Health), and melen-
gestrol acetate (Pﬁzer Animal Health, heifer diets only).
The DFM was shipped on ice and frozen (-20C) until use.
The DFM was measured daily to target 1 g/animal/d and
added to diets using cDDG carrier. Pens within a replicate
were fed equal amounts of cDDG, and VAC and CON pens
were fed prior to DFM pens to avoid cross-contamination.
Residual DFM diet in feed trucks was removed by feeding
Cattle were from two feedlots; with most allocation set 1
(AS1) cattle from Feedlot A and most allocation set 2
(AS2) from Feedlot B. Using new gloves for each animal,
feces (3–5 g) were rectally collected at feedlots A and B for
detection and enumeration of E. coli O157:H7. Cattle were
blocked by weight to facilitate marketing and stratiﬁed by
E. coli O157:H7 level (Negative, no E. coli O157:H7 de-
tected; Lower, insufﬁcient for enumeration; Higher, ‡1.6
log colony-forming units (CFU)/g feces) and randomized to
equate levels across pens within replicates (Table 1). Cattle
were then transported 110 km to the research feedlot and
penned as per previous randomization. Each pen contained
at least 1 animal from each feedlot, with an average of 70%
of AS1 cattle from Feedlot A and 80% of AS2 cattle from
Study experimental groups were as follows: DFM, ﬁn-
ishing diets containing BovamineCulture Complex
(Nutrition Physiology Company, LLC) with 10
L. acidophilus and Propionibacterium freudenreichii fed/
animal/d; VAC, standard ﬁnishing diets and 2 mL intramus-
cular injection of Econiche(Bioniche Life Sciences Inc.) at
allocation and 28 days later; or CON, standard ﬁnishing diets
only. The vaccine is licensed in Canada for 3 doses (28 days
apart), but the 2-dose regimen was approved by the manu-
facturer. Cattle were allocated on June 15 (AS1) and June 28
(AS2) 2011, respectively. Cattle (n=864) were housed by
allocation set and experimental group in 48 pens with 18
cattle/pen and 1 pen from each experimental group consti-
tuting a replicate. Pens of AS1 cattle (n=30) were steers
(initial weight 416.0 –27.2 kg), while pens of AS2 cattle
(n=18) were heifers (initial weight 402.1 –28.3 kg). Ex-
perimental groups were in contiguous pens in separate feedlot
alleys to avoid cross-contamination between interventions.
Cattle were observed daily for animal health, managed using
standard feedlot procedures, and followed for 103–145 days
until shipment to slaughter.
At 28-day intervals, rectal fecal samples were collected
from all cattle and perineal swabs were obtained from 4
random cattle/pen. All cattle were swabbed the day prior to
slaughter (last handling event). To collect perineal swabs,
a sterile SpongeSicle
(Med-Ox Diagnostics Inc., Ottawa,
ON) scrubbed an area 100 cm
below the anus and was
transported in 45 mL modiﬁed E. coli broth (mEC). Samples
were shipped chilled for processing within 24 h and stored at
5C until completion of analyses.
E. coli O157:H7 enumeration, detection
Each fecal sample was mixed to promote uniformity, and
two 1-g subsamples were enriched in 9 mL mEC (6 h at 37C).
Perineal swabs were incubated in mEC transport media (18 h at
37C). Enriched samples were subjected to immunomagnetic
separation (IMS) using anti-E. coli O157 Dynabeads
vitrogen, Carlsbad, CA). A 50-lL bead–bacteria mixture was
plated on sorbitol MacConkey agar with 2.5mg/L potassium
tellurite and 0.05mg/L ceﬁxime (CT-SMAC) and incubated
(18–24 h at 37C). Three sorbitol-negative colonies/plate were
evaluated using E. coli O157 latex tests (Oxoid, Nepean, On-
tario, Canada), with positive colonies frozen in glycerol.
For enumeration, 1:10 dilutions from 1-g fecal subsamples
positive by IMS were prepared in mEC with 20 mg/L novo-
biocin (EMD, Gibbstown, NJ), and 100-lL duplicates were
plated on CT-SMAC. Plates contained 30–300 sorbitol-
negative colonies, with 5 colonies latex tested for O157
Table 1. Balancing Escherichia coli O157:H7
Within Pens of 18 Cattle Across Experimental
Groups at Allocation
set E. coli O157 Control
CFU 1 1 1 3
LS 3 3 3
Negative 14 14 14
CFU 1 1 1 3
LS 3 3 3
Negative 14 14 14
CFU 1 1 1 3
LS 3 3 3
Negative 14 14 14
CFU 1 1 1 3
LS 3 3 3
Negative 14 14 14
CFU 1 1 1 3
LS 3 3 3
Negative 14 14 14
CFU 1 1 1 6
LS 3 3 3
Negative 14 14 14
Negative 11 11 11
Negative 12 12 12
Negative 13 13 13
CFU 1 1 1 3
Negative 17 17 17
CFU 1 1 1 3
Negative 17 17 17
Negative 15 15 15
Negative 16 16 16
Number of animals per experimental group.
DFM, direct-fed antimicrobials; CFU, colony-forming units; LS,
low-shedder detected by immunomagnetic separation.
380 STANFORD ET AL.
antigen. Number of colonies/plate was adjusted as described
by Stephens et al. (2009). From O157 colonies frozen in
glycerol, polymerase chain reaction (PCR) conﬁrmed E. coli
O157:H7 (Gannon et al., 1997; Paton and Paton, 1998).
Colonies were considered E. coli O157:H7 positive with
eaeA, ﬂiC, and at least one Shiga-toxin gene.
Pulsed-ﬁeld gel electrophoresis (PFGE)
A random subset of isolates conﬁrmed E. coli O157:H7
(n=42) balanced by allocation set; treatment and Shiga-toxin
proﬁle were subtyped by PFGE using XbaI restriction and
standard 1-d protocol (Ribot et al., 2006). One E. coli
O157:H7 isolate/positive sample was PFGE typed using a
CHEF DR II electrophoresis unit (Bio-Rad Laboratories,
Mississauga, ON). Banding patterns were viewed with UV
illumination and photographed using Speedlight Platinum
Gel Documentation System (Bio-Rad).
Analyses used SAS 9.2 (SAS Institute, Cary, NC) and were
considered signiﬁcant at p<0.05 with pen the experimental
unit. Repeated-measure analyses for E. coli O157:H7 enu-
meration used mixed-models including experimental group,
allocation set (AS), and days-on-trial as ﬁxed effects, with
three-way interaction of experimental group, AS and repli-
cate as a random effect and days-on-trial as repeated variable.
Prevalence of E. coli O157:H7 was analyzed using logistic
methodology within GLIMMIX and as signiﬁcant two- and
three-way interactions with AS were present, analyses were
performed by AS, with experimental group, sample type, and
days-on-trial as ﬁxed effects, and interaction of experimental
group and replicate as random effects. Model-adjusted means
(back-transformed to original scale) were reported, with ef-
ﬁcacy estimated using the formula:
Efficacy ¼[1 (prevalence for intervention=
prevalence for control)] ·100
The PFGE patterns were classed as unique or grouped into
restriction endonuclease digestion pattern clusters (REPC;
‡90% similarity) using Dice similarity coefﬁcients, un-
weighted-pair group methods arithmetic average algorithm,
1% position tolerance, and 0.5% optimization (BioNumerics
6.6, Applied Maths BVBA, Sin-Martens-Latem, Belgium).
Within- and between-group PFGE proﬁle similarities were
tested using Dimensioning Techniques. For these analyses,
band-matched binary character proﬁles were created after
clustering using Dice coefﬁcients. Bootstrap analysis (n=
1000) then assessed the similarity of PFGE proﬁles.
Results and Discussion
Study timing and location
Based on previous Alberta studies (Stanford et al., 2005a;
Stephens et al., 2009), peak E. coli O157:H7 prevalence
usually occurs during August and September. Consequently,
initial screening began in May, with cattle allocation by June.
FIG. 1. Fecal samples and perineal swabs positive for Escherichia coli O157:H7 and fecal samples with sufﬁcient E. coli
O157:H7 for enumeration (higher-shedder, ‡1.6 log colony-forming units/g feces) from steers (n=540) allocated on June
15, 2011 (AS1) and heifers (n=324), allocated on June 28, 2011 (AS2).
Day of sampling, pre-treat, prior to initiation of interventions, no perineal swabs collected; day 103 (AS1 only slaughter)
n=216; day 118 (AS2 only slaughter) n =151; day 131 slaughter n =158 (AS2), n =264 (AS1); day 145 (AS1 only
slaughter) n =53.
A VACCINE AND DFM FOR E. COLI O157:H7 381
At allocation, E. coli O157 shedding was balanced across
replicates and experimental groups (Table 1), with an average
of 10% fecal positives in AS1 and AS2 (Fig. 1). Monitoring
occurred during E. coli O157:H7 season, with cattle
slaughtered September through early November. Although
prevalence was highest in July ( p<0.001; Table 2), E. coli
O157:H7 was sufﬁciently prevalent for intervention com-
parison throughout the feeding cycle (Fig. 1).
Cattle were housed in small rather than in commercial pens
(200–400 animals/pen). Animal behavior and disease trans-
mission are known to differ in large- and small-pen com-
parisons ( Jim et al., 1993; Perrett et al., 2008); however,
identifying sufﬁcient E. coli O157:H7-positive cattle is a
challenge in large-pen studies. The small-pen design used
ensured adequate and initially balanced prevalence of E. coli
O157:H7 for experimental group comparisons and prevented
cross-contamination of interventions. The DFM dosage was
chosen to control E. coli O157:H7 as per past studies
(Younts-Dahl et al., 2004; Peterson et al., 2007a; Vascon-
celos et al., 2008) and has not previously improved feedlot
performance (Elam et al., 2003; Peterson et al., 2007a;
Vasconcelos et al., 2008).
Previous work evaluating pre-harvest interventions against
E. coli O157:H7 ensured sufﬁcient prevalence by inoculating
cattle with E. coli O157:H7 (Allen et al., 2011) or using
naturally colonized cattle sampled only during peak season
(Cull et al., 2012). In the present study, a single fecal sample
was used to balance E. coli O157:H7 levels across experi-
mental groups and ensure sufﬁcient prevalence as each pen
had at least one animal shedding E. coli O157:H7 prior
to initiation of interventions. Use of perineal swabs also en-
hanced detection as E. coli O157:H7 was 1.9 times more
likely ( p<0.001) to be detected from perineal swabs than
from feces (Table 2), even though swabs were collected from
4 of 18 cattle during the feeding period and feces were col-
lected from all cattle per pen.
E. coli O157:H7 enumeration
or greater CFU E. coli O157:H7/g
feces; Chase-Topping et al., 2008) have increased contami-
nation of hides of pen mates (Stephens et al., 2009) and beef
carcasses ( Jacob et al., 2010). In contrast to super-shedders,
most cattle positive for E. coli O157:H7 shed at relatively low
levels ( <100 CFU/g of feces) (Ferens and Hovde, 2011). As
less than 10% of cattle may be super-shedders (Chase-
Topping et al., 2008), cattle in this study were divided
between ‘‘lower-shedders’’ (detectable by IMS) and ‘‘higher-
shedders’’ (sufﬁcient E. coli O157:H7 to enumerate; ‡1.6
log CFU/g feces).
The number of higher-shedder cattle was reduced 71.4%,
by VAC ( p=0.008; Fig. 2), which likely reduced the load of
E. coli O157:H7 in VAC pens, although VAC impact on
shedding duration was not assessed. While overall incidence
of higher-shedders was reduced, VAC did not prevent cattle
from becoming higher-shedders; VAC cattle shed up to 10
CFU E. coli O157:H7/g feces 1 month after booster and be-
fore ﬁnal sampling (data not shown). Similar reductions in
higher-shedder cattle have been reported for siderophore
receptor-based vaccines (Fox et al., 2009; Cull et al., 2012).
For cattle shedding E. coli O157:H7, average number of
E. coli O157:H7 in feces did not differ by intervention, al-
though AS2 feces were approximately 1 log higher ( p=0.004)
than AS1 (Fig. 3). Previous response to VAC for numbers of
E. coli O157:H7 shed has varied. Potter et al. (2004) reported
signiﬁcant reductions in cattle inoculated with the organism,
while Moxley et al. (2009) suggested that naturally colonized
cattle shed relatively similar numbers regardless of VAC. For
DFM, previous responses have also been mixed, with fecal
E. coli O157:H7 numbers reduced at dosages of 10
(Stephens et al., 2007a), while a companion study found no
impact on numbers in cattle feces with DFM doses from 10
CFU/d (Stephens et al., 2007b).
E. coli O157:H7 detection
E. coli O157:H7 prevalence in samples and intervention
responses differed ( p=0.02) by AS (Figs. 4 and 5). For AS2,
neither intervention reduced E. coli O157:H7 prevalence.
Compared to CON, AS2 VAC and DFM cattle had increased
prevalence of E. coli O157:H7 in perineal swabs within the
feeding period and at exit sampling ( p<0.05). It is unlikely
that interventions promoted E. coli O157:H7 shedding
in AS2 cattle and would instead reﬂect high variability of
Table 2. Probability of Detecting Escherichia coli O157:H7 from Allocation Set 1
and Allocation Set 2
Cattle as Inﬂuenced by Sample Type (Fecal Grab
or Perineal Swab)and Days on Trial During the Feeding Period
Allocation set 1 Allocation set 2
Variable Odds ratio 95% CI Signiﬁcance Odds ratio 95% CI Signiﬁcance
Sample p<0.001 p<0.001
Perineal swab 1.9 1.5–2.5 2.7 1.8–4.0
Fecal grab 1.0 Referent 1.0 Referent
Days on trial
28 12.5 8.3–16.7 12.5 7.1–20.0
56 5.0 3.4–7.1 2.1 1.2–3.7
84 1.4 1.0–2.2 1.5 0.8–2.9
112 1.0 Referent 1.0 Referent
Allocation set 1, steers (n=540) allocated on June 15, 2011 into 30 pens.
Allocation set 2, heifers (n=324) allocated June 28, 2011 into 18 pens.
Includes both perineal swab and fecal grab positives.
CI, conﬁdence interval.
382 STANFORD ET AL.
shedding among individual AS2 cattle due to negligible
impact of interventions. In contrast, VAC reduced E. coli
O157:H7 prevalence in feces ( p=0.03) and in perineal swabs
(p=0.04) in AS1 cattle during the feeding period, although
neither reduction was signiﬁcant at exit sampling. Efﬁcacy of
VAC in AS1 during the feeding period for reducing E. coli
O157:H7 prevalence was 60% for feces and 56% for perineal
swabs (Fig. 4). For DFM, E. coli O157:H7 prevalence was
reduced ( p=0.01) in AS1 perineal swabs during the feeding
period, although not at exit sampling (Fig. 5). However, fecal
E. coli O157:H7 prevalence was never reduced in AS1
DFM-fed cattle. Having >10% of cattle positive for E. coli
O157:H7 prior to intervention initiation (Fig. 1) likely neg-
atively inﬂuenced DFM efﬁcacy as proposed DFM mecha-
nisms may be most effective prior to gastrointestinal tract
colonization with E. coli O157:H7 (Callaway et al., 2004).
Although AS1 and AS2 were steers and heifers, respec-
tively, gender would not likely impact intervention efﬁcacy.
A 2-week sampling schedule difference may have contrib-
uted to differing efﬁcacies, but if minor changes in sample
collection timing were responsible for these differences,
DFM and VAC would be of limited utility for controlling
E. coli O157:H7 in commercial livestock. Possibly, differ-
ences in E. coli O157:H7 populations for AS1 and AS2
inﬂuenced intervention impacts. From PCR analyses, toxin
gene frequencies differed between AS ( p=0.004; data not
shown), with 87% of isolates from AS2 having stx1 and stx2,
while 75% of isolates from AS1 cattle had only stx1. Al-
though stx2 has suppressed development of cellular immune
responses to E. coli O157:H7 in cattle (Hoffman et al., 2006),
evaluation of a subset of AS2 data excluding isolates with
stx2 did not improve efﬁcacy (data not shown). Matthews
CON DFM VAC
Number of samples
FIG. 2. Incidence of fecal samples with
sufﬁcient Escherichia coli O157:H7 for
enumeration ( ‡1.6 log colony-forming units
(CFU)/g) from day 28 until shipment to
slaughter for cattle
fed the direct-fed mi-
Company, LLC) at a dosage of 10
animal/d Lactobacillus acidophilus and
Propionibacterium freudenreichii starting
on day 0 (DFM), given a 2-mL intramus-
cular injection of Econiche
Sciences Inc., Belleville, Ontario, Canada)
on day 0, and a booster on day 28 (VAC), or
given standard feedlot diets without DFM
and not vaccinated (CON).
Experimental Groups with different su-
perscripts differ, P=0.008.
No effect of allocation set (P>0.05) on
incidence of enumerable samples ( ‡1.6 log
CFU E. coli O157:H7/g feces).
E. col i O157:H7 log CFU/ g feces
Experimental group by allocation set
CON-1 CON-2DFM-1 DFM-2VAC-1 VAC-2
FIG. 3. Average number of Escherichia coli O157:H7 per gram of feces by experimental group
and allocation set (1 or
for complete study period.
Columns with different superscripts differ (P=0.03); overall effect of allocation set (P=0.004).
Allocation set 1 (steers, n =540, allocated June 15, 2011); Allocation set 2 (heifers, n =324, allocated June 28, 2011).
Experimental groups: CON, control; DFM, fed the direct-fed microbial Bovamine
(Nutrition Physiology Company, LLC)
at a dosage of 10
CFU/animal/day Lactobacillus acidophilus and Propionibacterium freudenreichii starting on day 0;
VAC, given a 2 mL intramuscular injection of Econiche
(Bioniche Life Sciences, Belleville ON) on day 0 and a booster on
A VACCINE AND DFM FOR E. COLI O157:H7 383
FIG. 4. Overall impact of two doses of Econiche vaccine
(Bioniche Life Sciences Inc., Belleville, Ontario, Canada) on day
0 and a booster on day 28 on detection of Escherichia coli O157:H7 in feces and hide swabs from allocation set 1 (AS1; steers
allocated June 15, 2011) and allocation set 2 (AS2; heifers allocated June 28, 2011) during the feeding period (cumulative
incidence from day 56 to day 112) until shipment to slaughter (single-day incidence occurring day 103 to day 145).
Efﬁcacy of VAC.
NS, not signiﬁcant (P>0.05).
Negative, VAC prevalence of E. coli O157:H7 >Control (P<0.05).
FIG. 5. Overall impact of the direct-fed microbial (DFM) Bovamine
(Nutrition Physiology Company, LLC) fed to
allocation set 1 (AS1; steers allocated June 15, 2011) and allocation set 2 (AS2; heifers allocated June 28, 2011) at a dosage
colony-forming units (CFU) Lactobacillus acidophilus and Propionibacterium freudenreichii per animal per day
during the feeding period from day 0 until shipment to slaughter on detection of Escherichia coli O157:H7 in feces and hide
swabs during the feeding period (cumulative incidence from day 28 to day 112) until shipment to slaughter (single-day
incidence occurring day 103 to day 145).
NS, not signiﬁcant (P>0.05).
Efﬁcacy of DFM.
Negative, DFM prevalence of E. coli O157:H7 >Control (P<0.05).
et al. (2013) proposed that cattle shedding E. coli O157:H7
with stx2 were more likely to be super-shedders and that
presence of stx2 was a primary risk factor for human disease.
Consequently, reduced efﬁcacy of VAC in AS2 as compared
to AS1 cattle may limit impacts of VAC on human health.
Additional study is required regarding estimated impacts of
interventions on human health and the role of stx2 on inter-
Variable efﬁcacy of VAC and DFM in different populations
of cattle would be consistent with other studies. A review of
vaccines to reduce ruminant fecal shedding E. coli O157:H7
(Snedeker et al., 2012) concluded that care should be taken
interpreting ﬁndings due to variability among studies. When
pre-harvest and at-harvest outcomes were considered for either
type-III secreted proteins or siderophore receptor and porin
protein vaccines, meta-analysis also showed heterogeneous
results (Varela et al., 2012), although these authors found ho-
mogeneity in pre-harvest outcomes in two-dose studies of
VAC. As E. coli O157:H7 is a commensal organism not
causing disease in cattle, variable immune responses by ani-
mals may contribute to heterogeneous vaccine efﬁcacy (Sne-
deker et al., 2012). In the present study, VAC response varied
by AS for pre-harvest measures and did not impact at-harvest
measures of E. coli O157:H7 contamination.
A large-scale feedlot evaluation of DFM efﬁcacy (Cull
et al., 2012) also reported DFM ineffective for reducing fecal-
shedding of E. coli O157:H7, although these authors did not
measure hide contamination and used 10
CFU L. acid-
ophilus/head/d. Feeding the 10
CFU dosage, DFM previ-
ously reduced E. coli O157:H7 detection in feces and hides
(Brashears et al., 2003) or in feces but not hides (Younts-Dahl
et al., 2005; Stephens et al., 2007b). In this study, it is in-
triguing that both DFM and VAC interventions were most
effective in AS1 and did not control E. coli O157:H7 prev-
alence in AS2. More universally effective pre-harvest inter-
ventions are required, and the vaccine manufacturer in this
study has recently announced initiation of research for a
second-generation E. coli O157 vaccine (Anonymous, 2013).
PFGE genetic variability
From PFGE analyses, seven REPC and nine unique iso-
lates were detected, with most isolates from AS1 and AS2 in
separate REPC (data not shown). In REPC with co-mingling
of AS1 and AS2, only atypical AS2 isolates lacking stx2 were
present. Generally, isolates in REPC were from a single AS
and had similar stx genes; the only exception was REPC 6,
where AS1 cattle with stx1 or both stx1 and stx2 were present.
As AS1 and AS2 cohorts were mostly from different feedlots
and would have been penned separately at those feedlots as
well as in the present study, PFGE subtype bifurcation by AS
is not surprising. E. coli O157:H7 subtypes can vary by farm
(Rice et al., 1999; Stanford et al., 2005b) and by pen within
commercial feedlots (Sargeant et al., 2006; Stanford et al.,
2012), possibly related to the farm of origin of the cattle.
From bootstrapping analyses, AS1 isolates had more
similar PFGE proﬁles compared to all isolates ( p<0.001),
while AS2 isolates showed less uniformity ( p=0.08; Table
3). The PFGE proﬁling revealed that within-group similarity
of isolates with stx1 alone was higher than when compared to
all isolates ( p<0.001), while within-group similarity of
isolates with stx1 and stx2 genes was lower when compared
to all isolates ( p=0.11). Subdividing isolates with stx1 and
stx2 genes by AS, both sets of PFGE proﬁles were diverse.
Overall, PFGE analyses demonstrated that AS1 E. coli
O157:H7 subtypes were relatively homogeneous compared
to increased diversity of AS2 isolates. This may at least
partially explain the limited efﬁcacy of interventions for AS2.
Subtypes of E. coli O157:H7 from AS1 and AS2 may dif-
ferently express genes in the locus of enterocyte effacement
(LEE) encoding the type III proteins secretion system (Roe
et al., 2004). Alternatively, proteins other than those encoded
by LEE also contribute to E. coli O157:H7 adherence in the
bovine gastrointestinal tract (Kudva et al., 2012) and may be
more common in AS2. Studies to further characterize E. coli
O157:H7 isolates from AS1 and AS2 are in progress.
Although VAC reduced the numbers of cattle shedding
enumerable E. coli O157:H7, it did not prevent individuals
shedding up to 10
CFU/g feces. Neither VAC nor DFM
consistently reduced prevalence of E. coli O157:H7 in feces
or perineal swabs from either AS of cattle, and neither in-
tervention lowered numbers of E. coli O157:H7 shed in feces.
Intervention efﬁcacy may have been negatively inﬂuenced by
an initial shedding rate ( >10% of cattle) and presence of
different E. coli O157:H7 subtypes. As VAC and DFM had
variable efﬁcacy, additional development is required prior to
recommending either pre-harvest E. coli O157:H7 interven-
tion to the commercial beef industry.
This work was funded by the Alberta Livestock and Meat
Bioniche Life Sciences Inc. and Nutrition Physiology
Company LLC. contributed product and funding to Feedlot
Health Management Services Ltd. to collectively offset 9%
of project costs.
Table 3. Average Group Similarity of Pulsed-Field
Gel Electrophoresis (PFGE) Proﬁles by Source
of Escherichia coli O157:H7 Isolates Compared
to the Similarity of PFGE Proﬁles for All Isolates
By allocation set
AS1 20 70.72 66.02 p<0.001
AS2 22 67.95 66.02 p=0.08
By Stx genes
Stx1 only 20 71.30 66.05 p<0.001
Stx2 only 1 NA NA NA
Stx1 and Stx2 21 59.09 57.39 p=0.11
Having both Stx genes by allocation set
AS1 6 69.11 68.75 p=0.49
AS2 15 67.04 66.04 p=0.28
NA, not applicable as minimum of two needed for comparisons.
A VACCINE AND DFM FOR E. COLI O157:H7 385
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Address correspondence to:
Kim Stanford, PhD
Alberta Agriculture and Rural Development
5401-1st Avenue South
Lethbridge, Alberta, T1J 4V6
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