National-scale genotyping was a practical and efficient methodology for the quantification of the contributions of different sources to human Campylobacter infection. Combined with the knowledge that retail chicken is routinely contaminated with Campylobacter, these results are consistent with the view that the largest reductions in human campylobacteriosis in industrialized countries will come from interventions that focus on the poultry industry.

Hybridization between distantly related organisms can facilitate rapid adaptation to novel environments, but is potentially constrained by epistatic fitness interactions among cell components. The zoonotic pathogens Campylobacter coli and C. jejuni differ from each other by around 15% at the nucleotide level, corresponding to an average of nearly 40 amino acids per protein-coding gene. Using whole genome sequencing, we show that a single C. coli lineage, which has successfully colonized an agricultural niche, has been progressively accumulating C. jejuni DNA. Members of this lineage belong to two groups, the ST-828 and ST-1150 clonal complexes. The ST-1150 complex is less frequently isolated and has undergone a substantially greater amount of introgression leading to replacement of up to 23% of the C. coli core genome as well as import of novel DNA. By contrast, the more commonly isolated ST-828 complex bacteria have 10–11% introgressed DNA, and C. jejuni and nonagricultural C. coli lineages each have <2%. Thus, the C. coli that colonize agriculture, and consequently cause most human disease, have hybrid origin, but this cross-species exchange has so far not had a substantial impact on the gene pools of either C. jejuni or nonagricultural C. coli. These findings also indicate remarkable interchangeability of basic cellular machinery after a prolonged period of independent evolution.

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 >10 4 CFU g ؊1 . These 9% represented >96% of the total E. coli O157 produced by all animals tested. All isolates possessed the vt 2 gene, 39 had the eaeA gene, and a further five had the vt 1 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.Escherichia coli O157 was first identified as a food-borne pathogen in 1982 during an outbreak that was traced to contaminated hamburgers (20). The pathogen is associated with a range of symptoms, including watery or bloody diarrhea, vomiting, hemorrhagic colitis, and hemolytic uremic syndrome, which is characterized by acute renal failure affecting mainly children and the immunocompromised (7). While the majority of foods linked to human outbreaks of E. coli O157 are not assessed quantitatively, some studies have indicated a low infective dose (1, 26), highlighting the need for stringent control of contamination during food production.Cattle and other ruminants have been established as major natural reservoirs for E. coli O157 (18) and play a significant role in the epidemiology of human infections (7). It has been estimated that 1 to 4% of United Kingdom cattle are infected at slaughter (3,19), although more recently a prevalence rate of 8.6% has been reported from a farm study in Scotland (25). In the United States, breeding herd prevalences of 1% (21) and 9.3% (6) have been recorded, whereas in feedlot animals, rates have varied between 2.8% (4) and 35.8% (5). Prevalences in the summer months were usually greater than in the winter months. A number of environmental and food-borne sources have caused E. coli O157 incidents, with many attributed to the consumption of food of bovine origin (22) or with either direct or indirect contact with cattle and other farm animals (13).The concentration at which E. coli O157 is shed in feces varies from animal to animal as demonstrated in a North American study with calves (29), where a range from 10 2 to 10 5 CFU g Ϫ1 was observed. High-shedding sheep (excreting Ͼ10 4 CFU g Ϫ1 ) were responsible for the New Deer E. coli O157 outbreak in Scotland (16,23). High-shedding animals pose an elevated risk of contaminating the food chain if presented to slaughter. However, little published data are available on the concentration of E. coli O157 in cattle feces at the time of slaughter.The health risk from E. coli O157 and other pathogens is mi...

Homologous recombination between bacterial strains is theoretically capable of preventing the separation of daughter clusters, and producing cohesive clouds of genotypes in sequence space. However, numerous barriers to recombination are known. Barriers may be essential such as adaptive incompatibility, or ecological, which is associated with the opportunities for recombination in the natural habitat. Campylobacter jejuni is a gut colonizer of numerous animal species and a major human enteric pathogen. We demonstrate that the two major generalist lineages of C. jejuni do not show evidence of recombination with each other in nature, despite having a high degree of host niche overlap and recombining extensively with specialist lineages. However, transformation experiments show that the generalist lineages readily recombine with one another in vitro. This suggests ecological rather than essential barriers to recombination, caused by a cryptic niche structure within the hosts.

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.