Hazel I. Knight

Temporal shedding patterns and virulence factors of Escherichia coli serogroups O26, O103, O111, O145, and O157 in a cohort of beef calves and their dams

ABSTRACT This study investigated the shedding of Escherichia coli O26, O103, O111, O145, and O157 in a cohort of beef calves from birth over a 5-month period and assessed the relationship between shedding in calves and shedding in their dams, the relationship between shedding and scouring in calves, and the effect of housing on shedding in calves. Fecal samples were tested by immunomagnetic separation and by PCR and DNA hybridization assays. E. coli O26 was shed by 94% of calves. Over 90% of E. coli O26 isolates carried the vtx1, eae, and ehl genes, 6.5% carried vtx1 and vtx2, and one isolate carried vtx2 only. Serogroup O26 isolates comprised seven pulsed-field gel electrophoresis (PFGE) patterns but were dominated by one pattern which represented 85.7% of isolates. E. coli O103 was shed by 51% of calves. Forty-eight percent of E. coli O103 isolates carried eae and ehl, 2% carried vtx2, and none carried vtx1. Serogroup O103 isolates comprised 10 PFGE patterns and were dominated by two patterns representing 62.5% of isolates. Shedding of E. coli O145 and O157 was rare. All serogroup O145 isolates carried eae, but none carried vtx1 or vtx2. All but one serogroup O157 isolate carried vtx2, eae, and ehl. E. coli O111 was not detected. In most calves, the temporal pattern of E. coli O26 and O103 shedding was random. E. coli O26 was detected in three times as many samples as E. coli O103, and the rate at which calves began shedding E. coli O26 for the first time was five times greater than that for E. coli O103. For E. coli O26, O103, and O157, there was no association between shedding by calves and shedding by dams within 1 week of birth. For E. coli O26 and O103, there was no association between shedding and scouring, and there was no significant change in shedding following housing.

Prevalence and Virulence Factors of Escherichia coli Serogroups O26, O103, O111, and O145 Shed by Cattle in Scotland

ABSTRACT A national survey was conducted to determine the prevalence of Escherichia coli O26, O103, O111, and O145 in feces of Scottish cattle. In total, 6,086 fecal pats from 338 farms were tested. The weighted mean percentages of farms on which shedding was detected were 23% for E. coli O26, 22% for E. coli O103, and 10% for E. coli O145. The weighted mean prevalences in fecal pats were 4.6% for E. coli O26, 2.7% for E. coli O103, and 0.7% for E. coli O145. No E. coli O111 was detected. Farms with cattle shedding E. coli serogroup O26, O103, or O145 were widely dispersed across Scotland and were identified most often in summer and autumn. However, on individual farms, fecal shedding of E. coli O26, O103, or O145 was frequently undetectable or the numbers of pats testing positive were small. For serogroup O26 or O103 there was clustering of positive pats within management groups, and the presence of an animal shedding one of these serogroups was a positive predictor for shedding by others, suggesting local transmission of infection. Carriage of vtx was rare in E. coli O103 and O145 isolates, but 49.0% of E. coli O26 isolates possessed vtx, invariably vtx1 alone or vtx1 and vtx2 together. The carriage of eae and ehxA genes was highly associated in all three serogroups. Among E. coli serogroup O26 isolates, 28.9% carried vtx, eae, and ehxA—a profile consistent with E. coli O26 strains known to cause human disease.

Distribution of Escherichia coli O157 in Bovine Fecal Pats and Its Impact on Estimates of the Prevalence of Fecal Shedding

ABSTRACT The distribution of Escherichia coli O157 in bovine feces was examined by testing multiple samples from fecal pats and determining the density of E. coli O157 in immunomagnetic separation (IMS)-positive fecal samples. The density of E. coli O157 in bovine feces was highly variable, differing by as much as 76,800 CFU g−1 between samples from the same fecal pat. The density in most positive samples was <100 CFU g−1, the limit of reliable detection by IMS. Testing only one 1-g sample of feces per pat with IMS may result in a sensitivity of detection as low as 20 to 50%. It is therefore probable that most surveys have greatly underestimated the prevalence of E. coli O157 shedding in cattle and the proportion of farms with shedding cattle. The sensitivity of the detection of E. coli O157 in bovine feces can be as much as doubled by testing two 1-g samples per pat rather than one 1-g sample.

High-level genotypic variation and antibiotic sensitivity among Escherichia coli O157 strains isolated from two Scottish beef cattle farms.

ABSTRACT Escherichia coli O157:H7 is a human pathogen that is carried and transmitted by cattle. Scotland is known to have one of the highest rates of E. coli O157 human infections in the world. Two hundred ninety-three isolates were obtained from naturally infected cattle and the environment on two farms in the Scottish Highlands. The isolates were typed by pulsed-field gel electrophoresis (PFGE) with XbaI restriction endonuclease enzyme, and 19 different variations in patterns were found. There was considerable genomic diversity within the E. coli O157 population on the two farms. The PFGE pattern of one of the observed subtypes matched exactly with that of a strain obtained from a Scottish patient with hemolytic-uremic syndrome. To examine the stability of an individual E. coli O157 strain, continuous subculturing of a strain was performed 110 times. No variation from the original PFGE pattern was observed. We found three indistinguishable subtypes of E. coli O157 on both study farms, suggesting common sources of infection. We also examined the antibiotic resistance of the isolated strains. Phenotypic studies demonstrated resistance of the strains to sulfamethoxazole (100%), chloramphenicol (3.07%), and at a lower rate, other antibiotics, indicating the preservation of antibiotic sensitivity in a rapidly changing population of E. coli O157.

Analysis of Feces Samples Collected from a Wild-Bird Garden Feeding Station in Scotland for the Presence of Verocytotoxin-Producing Escherichia coli O157

ABSTRACT Composite wild bird feces collected at regular intervals from a garden feeding station in southwest Scotland over a 3-year period were examined for verocytotoxin-producing Escherichia coli O157. One sample was positive for Escherichia coli O157. The isolate belonged to phage type 21/28 and possessed vtx2, eaeA, and enterohemorrhagic E. coli hlyA genes.

Age-related decline in carriage of ampicillin-resistant Escherichia coli in young calves.

ABSTRACT The presence of ampicillin-resistant Escherichia coli (AmprE. coli) in the fecal flora of calves was monitored on a monthly basis in seven cohorts of calves. Calves were rapidly colonized by AmprE. coli, with peak prevalence in cohort calves observed in the 4 months after the calves were born. The prevalence of calves yielding AmprE. coli in cohorts consistently declined to low levels with increasing age of the calves (P < 0.001).

Prevalence of Escherichia coli O157 : H7 and serogroups O26, O103, O111 and O145 in sheep presented for slaughter in Scotland

Sheep have been proposed as a source of human verocytotoxigenic Escherichia coli infection on a number of occasions but few prevalence studies have focused on identifying rates of carriage of these pathogens in this species. The purpose of this work was to establish the frequency of excretion of E. coli of serogroups O157, O26, O103, O111 and O145 in sheep presented for slaughter in Scotland and to examine their carriage of known virulence determinants. The study involved microbiological isolation of E. coli from 1082 sheep presented for slaughter in four Scottish abattoirs between July 2005 and June 2006. Using faecal enrichment and immunomagnetic separation, the isolation rate from these samples was 3.4 % for E. coli serogroup O157, 5.2 % for E. coli serogroup O26, 2.3 % for E. coli serogroup O103 and 0.1 % for E. coli serogroup O145. E. coli O111 was not isolated. In the last month of testing, which coincided with sorbitol-fermenting E. coli O157 (SFO157) cases in children in Scotland, all 83 recta received were screened and tested negative for SFO157 strains. The study found no verocytotoxin-positive strains amongst the E. coli serogroup O103 or O145 isolates. Verocytotoxin-positive strains were identified amongst isolates of E. coli serotypes O157 : H7 and O26 : H11. E. coli O157 : H7 was not isolated from samples collected between January and March, a statistically significant drop (P<0.001) in mean shedding relative to other months. There was evidence (P = 0.003) of higher shedding of O157 in adults and hoggs than in lambs. E. coli O26 : H11 was isolated throughout the year, with a statistically significant peak in shedding in the third quarter (P = 0.003). The results showed that sheep presented for slaughter in Scotland may carry strains of E. coli, particularly of serogroups O157 and O26, which can be presumed to have potential to cause human infection. They did not support a hypothesis that human cases of E. coli O157 : H7 are higher in any particular Scottish region as a direct consequence of a higher rate of faecal carriage in sheep in that region.

Detection of genetic diversity by pulsed-field gel electrophoresis among Escherichia coli O157 isolated from bovine faecal samples by immunomagnetic separation technique

Aims:  Escherichia coli O157 is considered to be one of most important human pathogens of animal origin which causes serious clinical complications. One of the most common methods to isolate E. coli O157 is the immunomagnetic separation (IMS) technique which employs specific antibodies coupled to magnetic beads to bind and extract cells from enrichment broths followed by plating onto sorbitol MacConkey agar supplemented with cefixime and potassium tellurite (CT‐SMAC) plates. The aim of this study was to determine strain variation by pulsed‐field gel electrophoresis (PFGE) among E. coli O157 on IMS/CT‐SMAC plates.

Comparison of diversities of Escherichia coli O157 shed from a cohort of spring-born beef calves at pasture and in housing

ABSTRACT A cohort of spring-born beef calves demonstrated limited genetic and phenotypic diversity of Escherichia coli O157 when kept in a state of isolation. Despite this, there was a difference in the pulsed-field gel electrophoresis and phage types of isolates shed by cattle at pasture compared with those shed by the same cattle when weaned and housed.

Sensitivity of an Immunomagnetic-Separation-Based Test for Detecting Escherichia coli O26 in Bovine Feces

ABSTRACT The sensitivity of a test for cattle shedding Escherichia coli serogroup O26 was estimated using several fecal pats artificially inoculated at a range of concentrations with different E. coli O26 strains. The test involves the enrichment of fecal microflora in buffered peptone water, the selective concentration of E. coli O26 using antibody-coated immunomagnetic-separation beads, the identification of E. coli colonies on Chromocult tryptone bile X-glucuronide agar, and confirmation of the serogroup with E. coli serogroup O26-specific antisera using slide agglutination. The effective dose of E. coli O26 for an 80% test sensitivity (ED80) was 1.0 × 104 CFU g−1 feces (95% confidence interval, 4.7 × 103 to 2.4 × 104). Differences in test sensitivity between different E. coli O26 strains and fecal pats were also observed. Individual estimates of ED80 for each strain and fecal pat combination ranged from 4.2 × 102 to 4.8 × 105 CFU g−1. These results suggest that the test is useful for identifying individuals shedding a large number of E. coli O26 organisms or, if an appropriate number of individuals in a herd are sampled, for identifying affected herds. The study also provides a benchmark estimate of sensitivity that can be used to compare alternative tests for E. coli O26 and a methodological approach that can be applied to tests for other pathogenic members of the Enterobacteriaceae and other sample types.