Insight into the Genome of Brochothrix thermosphacta, a Problematic Meat Spoilage Bacterium

Abstract

Brochothrix thermosphacta is a dominant but poorly studied meat spoilage organism. It is a close relative of the foodborne pathogen Listeria monocytogenes, and Brochothrix constitutes the second genus in the Listeriaceae family. Here, the genomes of 12 B. thermosphacta strains were sequenced, assembled into draft genomes, characterized, and compared with the genomes of Brochothrix campestris and L. 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 the B. thermosphacta strains, 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 of Listeria virulence 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 the Brochothrix genome, 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.IMPORTANCE Despite 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. thermosphacta contributes substantially to spoilage-associated losses. Nonetheless, this organism and particularly its genome remain largely unstudied. This study contributes to improving our knowledge of the Brochothrix genus. 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 of Brochothrix and establishing parallels to and differences from the closely related foodborne pathogen L. monocytogenes.KEYWORDS Brochothrix, Listeria monocytogenes, meat spoilage, spoilage B rochothrix thermosphacta is one of the most abundant spoilage organisms of fresh and cured meats, fish, and fish products, due to its tolerance to high-salt and low-pH conditions, its ability to grow at refrigeration tempera...

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