Marion MacRae

Concentration and prevalence of Escherichia coli O157 in cattle feces at slaughter.

ABSTRACT The concentration and prevalence of Escherichia coli O157 in cattle feces at the time of slaughter was studied over a 9-week period from May to July 2002. Fecal samples (n = 589) were collected from the rectums of slaughtered cattle, and the animal-level prevalence rate was estimated to be 7.5% (95% confidence interval [CI], 5.4 to 9.6%) while the group prevalence was 40.4% (95% CI, 27.7 to 53.2%). Of the 44 infected animals detected, 9% were high shedders that contained E. coli O157 at concentrations of >104 CFU g−1. These 9% represented >96% of the total E. coli O157 produced by all animals tested. All isolates possessed the vt2 gene, 39 had the eaeA gene, and a further five had the vt1 gene also. The presence of high-shedding animals at the abattoir increases the potential risk of meat contamination during the slaughtering process and stresses the need for correctly implemented hazard analysis and critical control point procedures.

Campylobacter genotypes from food animals, environmental sources and clinical disease in Scotland 2005/6

A nationwide multi-locus sequence typing (MLST) survey was implemented to analyze patterns of host association among Campylobacter jejuni and Campylobacter coli isolates from clinical disease in Scotland (July 2005-September 2006), food animals (chickens, cattle, sheep, pigs and turkey), non-food animals (wild birds) and the environment. Sequence types (STs) were determined for 5247 clinical isolates and 999 from potential disease sources (augmented with 2420 published STs). Certain STs were over represented among particular sample sets/host groups. These host-associated STs were identified for all sample groups in both Campylobacter species and host associated clonal complexes (groups of related STs) were characterized for C. jejuni. Some genealogical lineages were present in both human disease and food animal samples. This provided evidence for the relative importance of different infection routes/food animal sources in human disease. These results show robust associations of particular genotypes with potential infection sources supporting the contention that contaminated poultry is a major source of human disease.

Long-term survival of Escherichia coli O157 on pasture following an outbreak associated with sheep at a scout camp

Aims: To monitor the decay of E. coli O157 in soil (loamy sand) on a scout campsite following an outbreak in humans.

Has Retail Chicken Played a Role in the Decline of Human Campylobacteriosis

ABSTRACT Between 2001 and 2006, the incidence of human Campylobacter infections decreased by 10 and 27% in Scotland and the Grampian region of Scotland, respectively. Contemporaneous collection and analyses of human and retail-chicken isolates from Grampian were carried out over a 10-week period in 2001 and again in 2006 in order to determine whether the fall in the incidence of human infections was related to the retail-chicken exposure route. Rates of carriage of Campylobacter on chicken carcasses from retail outlets in Grampian in 2001 and 2006 were estimated. Chicken-derived Campylobacter isolates from 2001 (n = 84) and 2006 (n = 105) and human-derived isolates from patients with clinical cases of infection in 2001 (n = 172) and 2006 (n = 119) were typed by multilocus sequence typing. We found no evidence for statistically significant changes in prevalence and counts per carcass. We found by rarefaction that although the degree of diversity in humans tended to be higher than that in chickens, these differences were not significant. The genetic distance between chicken and human isolates from 2001 according to sequence type, clonal complex (CC), or allele composition was not significant, whereas the distances between 2006 isolates at the CC and allele levels were significant. This difference was attributable to a lower proportion of CC-21s being found in retail-chicken isolates from 2006 than in chicken isolates from 2001. We conclude that human exposure to Campylobacter via retail chicken is important and that changes in the population structure of campylobacters in this reservoir need to be taken into account in investigating human infection.

Campylobacter excreted into the environment by animal sources: prevalence, concentration shed, and host association.

An intensive study of 443 isolates of Campylobacter jejuni and Campylobacter coli from 2031 fecal samples excreted by animal sources including cattle, sheep, and pigs, a range of wild and domesticated avian species and pets is described. The prevalence found in the majority of animal sources ranged from 22% to 28% with poultry being highest at 41% and cats and dogs lowest (<5%). The average count excreted for each animal source was found not to be significantly different ranging from approximately 10(2) to 10(5) cfu/g. Multilocus sequence typing (MLST) identified phylogenies that exhibited host specificity. A number of clonal complexes (CCs) and sequence types (STs) were characteristic of particular hosts (e.g., CC-179, ST-637, and ST-1341 found only in pigeons and gulls). Analysis of genetic distance demonstrated numerous significant differences in the distribution of MLST types (CC, ST, and allele) between animal sources. Host association was quantified using structure that correctly assigned the nine animal sources with accuracies of 28%, 24%, and 55% at the CC, ST, and allele levels, respectively. This is substantially higher than would be expected by random allocation (11%) but farmyard poultry had the lowest assignment accuracy (13%, 13%, and 21%) suggesting that isolates were shared with a wide range of other animals. This study demonstrates the link between MLST type and host and provides data that can be used in risk assessment and food attribution models. Further, it demonstrates the applicability of MLST to characterize Campylobacter strains from a broad range of environmental sources.

Concentration and prevalence of Escherichia coli O157 in sheep faeces at pasture in Scotland

Aims:  To study the presence, numbers and virulence profiles of Escherichia coli O157 in sheep faeces and validate the microbiological methods used to attain these data.

The detection of non‐O157 E. coli in food by immunomagnetic separation

Aims:  To compare immunomagnetic separation (IMS) protocols (enrichment media and temperature) for the isolation of Escherichia coli serotypes O26 and O111 from four different foods.

Slugs: Potential Novel Vectors of Escherichia coli O157

ABSTRACT Field and laboratory studies were performed to determine whether slugs could act as novel vectors for pathogen (e.g., Escherichia coli O157) transfer from animal feces to salad vegetables. Escherichia coli O157 was isolated from 0.21% of field slugs from an Aberdeenshire sheep farm. These isolates carried the verocytotoxin genes (vt1 and vt2) and the attaching and effacing gene (eae), suggesting that they are potentially pathogenic to humans. Strain typing using multilocus variable number tandem repeats analysis showed that slug and sheep isolates were indistinguishable. Laboratory experiments using an E. coli mutant resistant to nalidixic acid showed that the ubiquitous slug species Deroceras reticulatum could carry viable E. coli on its external surface for up to 14 days. Slugs that had been fed E. coli shed viable bacteria in their feces with numbers showing a short but statistically significant linear log decline. Further, it was found that E. coli persisted for up to 3 weeks in excreted slug feces, and hence, we conclude that slugs have the potential to act as novel vectors of E. coli O157.

The optimization of isolation media used in immunomagnetic separation methods for the detection of Escherichia coli O157 in foods.

Aims: To compare media used in immunomagnetic separation (IMS) techniques for the isolation of Escherichia coli O157 from food.

Source attribution, prevalence and enumeration of Campylobacter spp. from retail liver

Campylobacter prevalence from retail liver (chicken, cattle, pig and sheep) was found to be 81%, 69%, 79% and 78% respectively. Molecular source attribution demonstrated that strains from chicken liver were most similar to those found commonly in humans. This provides further evidence of liver being a probable source of human infection.