ARS | Publication request: Use of agar diffusion assay to measure bactericidal activity of alkaline salts of fatty acids against bacteria associated with poultry processing

Submitted to: International Poultry Scientific Forum
Publication Type: Abstract Only
Publication Acceptance Date: October 13, 2010
Publication Date: January 24, 2011
Citation: Hinton Jr, A., Ingram, K.D. 2011. Use of agar diffusion assay to measure bactericidal activity of alkaline salts of fatty acids against bacteria associated with poultry processing [abstract]. International Poultry Scientific Forum. #56. p. 17.

Technical Abstract: The agar diffusion assay was used to examine antibacterial activity of alkaline salts of caproic, caprylic, capric, lauric, and myristic acids. A 0.5M concentration of each fatty acid was dissolved in 1.0 M potassium hydroxide (KOH), and pH of the mixtures was adjusted to 10.5 with citric acid. Solutions were filter sterilized by passage through 0.2 µm filters. Agar media was inoculated with 106 colony-forming-units/ml of Acinetobacter calcoaceticus, Campylobacter jejuni, Enterococcus faecalis, Escherichia coli, Listeria monocytogenes, Pseudomonas aeruginosa, Salmonella Typhimurium, or Staphylococcus simulans. Wells were made in solidified agar, and 0.1 ml of each solution was added to separate wells. Plates were incubated for 24-48 h aerobically at 35oC, except for C. jejuni plates incubated microaerobically at 42oC. Zones of inhibition of bacterial growth around the wells were measured. Results indicated that caproic acid-KOH inhibited growth of C. jejuni only. Caprylic acid-KOH inhibited growth of 3 of the Gram negative isolates, and the relative size of the zones of inhibition of the isolates were E. coli < P. fluorescens and C. jejuni. Only capric-KOH and lauric acid-KOH exhibited antibacterial activity towards all 8 isolates. Size of the zones of inhibition produced by capric acid-KOH was Salmonella Typhimurium < E. coli < A. calcoaceticus < L. monocytogenes and S. simulans < P. fluorescens < E. faecalis < C. jejuni. The relative size of the zones of inhibition produced by lauric acid-KOH was E. coli < A. calcoaceticus < Salmonella Typhimurium and E. faecalis < C. jejuni, S. simulans, and P. fluorescens < L. monocytogenes. Myristic acid-KOH was only inhibitory towards the 2 Gram positive cocci, and the size of the zones of inhibition for E. faecalis was significantly larger than the zones for S. simulans. Findings demonstrated that alkaline salts of FA possess antibacterial activity towards bacteria associated with poultry processing and that the agar diffusion assay can be used to screen antibacterial activity of these solutions.