Aims: To determine the prevalence and concentration of Escherichia coli O157 shed in faeces at slaughter, by beef cattle from different production systems. Methods and Results: Faecal samples were collected from grass-fed (pasture) and lot-fed (feedlot) cattle at slaughter and tested for the presence of E. coli O157 using automated immunomagnetic separation (AIMS). Escherichia coli O157 was enumerated in positive samples using the most probable number (MPN) technique and AIMS and total E. coli were enumerated using Petrifilm. A total of 310 faecal samples were tested (155 from each group). The geometric mean count of total E. coli was 5 × 10⁵ and 2·5 × 10⁵ CFU g⁻¹ for lot- and grass-fed cattle, respectively. Escherichia coli O157 was isolated from 13% of faeces with no significant difference between grass-fed (10%) and lot-fed cattle (15%). The numbers of E. coli O157 in cattle faeces varied from undetectable (<3 MPN g⁻¹) to 1·1 × 10⁵ MPN g⁻¹. Twenty-six (67%) of 39 O157 positive faeces had <10 MPN g⁻¹ and three (8%) had counts between 10³–10⁵ MPN g⁻¹. There was no significant difference between concentrations of E. coli O157 in the faeces of grass-fed or lot-fed cattle. Conclusion: The prevalence and numbers of E. coli O157 in the faeces of cattle at slaughter were not affected by the production systems evaluated in this study. Significance and Impact of the Study: Information on the prevalence and numbers of E. coli O157 can be used for formulating intervention strategies and in quantitative risk assessments.

Brochothrix thermosphactais a dominant but poorly studied meat spoilage organism. It is a close relative of the foodborne pathogenListeria monocytogenes, andBrochothrixconstitutes the second genus in theListeriaceaefamily. Here, the genomes of 12B. thermosphactastrains were sequenced, assembled into draft genomes, characterized, and compared with the genomes ofBrochothrix campestrisandL. monocytogenes. Phenotypic properties including biogenic amine production and antibiotic and heavy metal susceptibilities were tested. Comparative genomic analyses revealed a high degree of similarity among theB. thermosphactastrains, with bacteriophage genes constituting a significant proportion of the accessory genome. Genes for the production of the malodorous compounds acetate, acetoin, butanediol, and fatty acids were found, as were stress response regulatory genes, which likely play important roles in the spoilage process. Amino acid decarboxylases were not identified in the genomes, and phenotypic testing confirmed their absence. Orthologs ofListeriavirulence proteins involved in virulence regulation, intracellular survival, and surface protein anchoring were found; however, key virulence genes were absent. Analysis of antibiotic susceptibility showed that strains were sensitive to the four tested antibiotics, except for one tetracycline-resistant isolate with plasmid-mediated tetracycline resistance genes. Strains tolerated higher levels of copper and cobalt than of cadmium although not at concentrations high enough to categorize the strains as being resistant. This study provides insight into theBrochothrixgenome, links previous phenotypic data and data provided here to the gene inventory, and identifies genes that may contribute to the persistence of this organism in the food chain.IMPORTANCEDespite increasing knowledge and advances in food preservation techniques, microbial spoilage of foods causes substantial losses, with negative social and economic consequences. To better control the contamination and microbial spoilage of foods, fundamental knowledge of the biology of key spoilage bacteria is crucial. As a common meat spoilage organism,B. thermosphactacontributes substantially to spoilage-associated losses. Nonetheless, this organism and particularly its genome remain largely unstudied. This study contributes to improving our knowledge of theBrochothrixgenus. Spoilage-relevant pathways and genes that may play a role in the survival of this organism in a food processing environment were identified, linking previous phenotypic data and data provided here to the gene inventory ofBrochothrixand establishing parallels to and differences from the closely related foodborne pathogenL. monocytogenes.