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Acetoacetic acid impact on bacterial biofilms among a variety of strains.

Background: Bacterial biofilms are complex communities of bacteria that may attach to surfaces. A few examples include medical devices, such as catheters and artificial joints, and industrial equipment important in the food processing industry. This intimate association between bacteria and a surface allows for a vastly increased resistance to antibiotics as well as an increased difficulty of removal. Previous work in our lab used Escherichia coli O157:H7 in beef broth medium supplemented with a series of carbon and nitrogen sources to identify candidates for biofilm reduction [Lynnes et al., Meat Science, 2014]. Acetoacetic acid (AAA) was shown to reduce biofilm amounts of E. coli O157:H7. AAA has also been used in conjunction with other organic acids to inhibit growth of Listeria monocytogenes in the food processing industry. [Stasiewicz et al., Appl Environ Microbiol., 2011] The goal of this study is to demonstrate AAA's efficacy as a useful chemical inhibitor of bacterial biofilms.

Methods: Overnight cultures of Cronobacter sakazakii 894, Serratia marcescens 1591, and Yersinia enterocolitica 8081c were inoculated into tryptic soy broth supplemented with AAA at concentrations ranging from 0mg/mL to 40mg/mL. The bacteria were incubated on 24 well polystyrene plates at temperatures ranging from 25[degrees]C to 37[degrees]C for either 16 or 24 hours. The effect on growth was determined using the maximum velocity rate, effect on biofilm was determined using either a crystal violet assay or an ATP assay, and the 50% inhibitory concentration ([IC.sub.50]) for growth and biofilm amounts was determined using Masterplex ReaderFit dose-response software.

Results: The addition of AAA to the growth medium was shown to have an inhibitory effect for all strains tested in both biofilm formation and growth. The figure to the right shows the effect on Y. enterocolitica 8081c at 37[degrees]C. This general trend is seen across all other strains and conditions, while the [IC.sub.50] values varied among the strains and different growth temperatures.

The Y. enterocolitica 8081c incubated at 25[degrees]C had lowest [IC.sub.50], showing the most sensitivity to AAA, while this strain at 37[degrees]C and the S. marsescens strain had the most resistance to the supplement.

Conclusion: AAA can be an effective supplement at decreasing the growth and biofilm amounts for various bacterial strains at specific incubation temperatures. The inhibitory effects are more pronounced in Y. enterocolitica incubated at lower temperatures. This information may be useful when considering the use of AAA in food processing environments verses use in a medical setting.

Murphy, J.M., Home, S., Pruss, B.M.

Dept. of Veterinary and Microbiological Sciences, North Dakota State University, Fargo, ND

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Title Annotation:Graduate Communications IN THE A. RODGER DENISON COMPETITION
Author:Murphy, J.M.; Horne, S.; Pruss, B.M.
Publication:Proceedings of the North Dakota Academy of Science
Article Type:Author abstract
Date:Apr 1, 2015
Words:440
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