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ARS Home » Northeast Area » Beltsville, Maryland (BARC) » Beltsville Agricultural Research Center » Environmental Microbial & Food Safety Laboratory » Research » Publications at this Location » Publication #319777
Title: Biofilm formation by environmental isolates of Salmonella and their sensitivity to natural antimicrobials

Author
item KEELARA, SHIVARAMU - University Of Maryland
item Patel, Jitu
item SIDDHARTHA, THAKUR - North Carolina State University

Submitted to: Foodborne Pathogens and Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/9/2016
Publication Date: 6/23/2016
Citation: Keelara, S., Patel, J.R., Siddhartha, T. 2016. Biofilm formation by environmental isolates of Salmonella and their sensitivity to natural antimicrobials. Foodborne Pathogens and Disease. 13(9):509-516.

Interpretive Summary: Salmonella isolates from swine farm environments were evaluated for biofilm formation using microtitre and the novel Minimum Biofilm Eradication Concentration (MBEC) assay. All 15 Salmonella isolates formed biofilms as observed by MBEC assay. Hydrophobicity (%) varied with strain and growth phase of the strain, although the differences were not significant. There was no correlation between hydrophobicity, curli expression (a cell appendage used in attachment to surfaces) and biofilm formation of these strains. Antimicrobial activity of essential oils, cinnamaldehyde and sporran, was significant against Salmonella in biofilms. A 2000 ppm solution of these natural antimicrobials reduced Salmonella in biofilms by 6 logs; initial populations were 7-7.5 log/cm2. The bactericidal effect of these antimicrobials increased with their concentrations; Salmonella were undetectable when 3000 ppm of cinnamaldehyde or sporan was used. These results indicate that antimicrobials such as cinnamaldehyde and sporan can be used to kill Salmonella in biofilms. This information will be of interest to other scientists, produce farmers and regulatory agencies.

Technical Abstract: We evaluated 15 Salmonella isolates; S. Derby (2), S. Infantis (4), and S. Typhimurium (9) from conventional swine farm environment (soil and lagoon) for biofilm formation. Biofilm forming ability was determined by 96-well microtitre plate Crystal-Violet and Minimum Biofilm Eradication Concentration (MBEC) assays. The curli expression was robust among strains S322 and S435 (S. Infantis), S644, S777, S931, S953 and S977 (S. Typhimurium) as observed by Congo red dye binding assay. The cell hydrophobicity varied with strains and growth phase of the strain; the difference was not significant. Natural antimicrobials were evaluated with MBEC assay to kill Salmonella in biofilms. Cinnamaldehyde and sporan at 2000 ppm reduced (P< 0.05) Salmonella in biofilm by 6 log CFU from their initial populations of 7-7.5 log CFU/cm2. The bactericidal effect of these antimicrobials increased with their concentrations; Salmonella were undetectable when 3000 ppm of cinnamaldehyde or sporan was used. PCR was unable to detect bapA gene associated with biofilm formation in Salmonella. Natural antimicrobials such as cinnamaldehyde and sporan at 3000 ppm conc. can be used to kill Salmonella in biofilms.