Biofilm-forming Abilities of Salmonella Serovars Isolated From Clinically Ill Livestock at 48 and 168 h

Little is known regarding the biofilm-forming capabilities of a somewhat distinct population of Salmonellae present on-farm and responsible for illnesses in livestock and humans. Evaluation of cleaning and disinfection in preharvest environments has found little success in eradicating Salmonella biofilms to date. Disrupting the environmental survival of Salmonella via biofilm removal will be critical to reducing carriage in livestock reservoirs and the risk of foodborne illness. Therefore, the objective of this study was to characterize the biofilm-forming abilities of Salmonellae relevant to livestock and human health. Eighty-one isolates from 8 serovars (S. Typhimurium, Heidelberg, Montevideo, Agona, Newport, Dublin, 4,[5],12:i:-, Enteritidis) were sourced from poultry and clinically ill cattle, swine, and equine. We hypothesized that biofilm production rate would vary significantly between serovars, and biofilm density would increase from 48 to 168 hrs. Isolates were grown in 24-well microplates in tryptone soy broth at ambient temperature, with media refreshed every 48 h. Biofilm density was quantified using crystal violet assays. Strong biofilm formers comprised 84% (68/81) of isolates tested, while 5.9% (4/81) were considered weak. Biofilm density was significantly greater at 168 h versus 48 h for all serovars except Dublin. Additionally, biofilm growth rate varied by serovar. Differences in biofilm-associated genes were evaluated, and only the detection of csrB was significantly associated with the categorization of biofilm producers. Results suggest inconsistent cleaning likely allows for the establishment of biofilms in on-farm environments. Further, some serovars may pose a greater risk for rapid biofilm establishment. This study provides data necessary to inform the development of evidence-based cleaning and disinfection protocols effective against the most prolific biofilm-forming strains of virulent Salmonella.