Submitted to: Canadian Journal of Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/16/2020
Publication Date: 3/2/2020
Citation: Chen, C., Nguyen, L.T., Paoli, G., Irwin, P. 2020. The complex multicellular morphology of the food spoilage bacteria Brochothrix thermosphacta strains isolated from ground chicken. Canadian Journal of Microbiology. 66(4):303-312.
Interpretive Summary: Despite the significant economic impact of food spoilage, a detailed understanding of the microbial contributors to meat spoilage is lacking. Brochothrix thermosphacta is a bacterium commonly associated with spoilage of meat, poultry, and seafood. Here we describe a unique type of bacterial growth exhibited by strains of B. thermosphacta isolated from chicken. Whereas most bacteria grow as individual microscopic cells or small clusters of cells, these isolates of B. thermosphacta grow as long filaments of cells that form even larger complex structures (i.e., clustered balls or sheets of cells) large enough to be visible to the naked eye. Though these large complex structures have not been observed when B. thermosphacta is grown on food it is thought that, in addition to causing food spoilage, microscopic aggregates of B. thermosphacta might serve to provide a microenvironment that could be beneficial to the growth and/or persistence of foodborne pathogenic bacteria.
Technical Abstract: Herein we describe a highly structured, filamentous growth phenotype displayed by an isolate of the food spoilage microorganism Brochothrix thermosphacta. The growth morphology of this strain of B. thermosphacta (strain BII) was dependent on environmental factors such as the growth media, incubation temperatures, and the inoculum concentration. Inoculation of cultures in highly dilute suspensions resulted in the formation of isolated, tight aggregates resembling fungal growth in liquid media. This same strain also formed stable, mesh-like structures in 6-well tissue culture plates under specific growth conditions. The complex growth phenotype does not appear to be unique to strain BII but was common among B. thermosphacta strains isolated from chicken. Light and electron micrographs showed that the filaments of multiple BII cells can organize into complex, tertiary structures resembling multi-stranded cables. Time-lapse microscopy was employed to monitor the development of such aggregates over 18 hours and revealed growth originating from short filaments into compact ball-like clusters that appeared fuzzy due to protruding filaments or cables. This report is the first to document this complex filamentous growth phenotype in a wild-type bacterial isolate of B. thermosphacta.