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

Brochothrix thermosphacta is a dominant, but poorly studied meat spoilage organism. It is a close relative of the foodborne pathogen Listeria monocytogenes and constitutes the second genera 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 susceptibility 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 malodourous 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 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 resistant.

This study provides insight into the Brochothrix genome, links previous phenotypic data and data provided here to gene inventory and identifies genes that may contribute to the persistence of this organism in the food chain.