Submitted to: Journal of Food Protection
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: June 6, 2006
Publication Date: November 11, 2006
Citation: Bayles, D.O., Uhlich, G.A. 2006. Mutations in crp/fnr family of regulatory genes in listeria monocytogenes strain f2365 do not alter heat resistance at 60 degrees c. Journal of Food Protection. 69:2758-2760. Interpretive Summary: The Listeria monocytogenes genome contains a class of regulatory genes (Crp/Fnr) that are present in large numbers; however, members of this same class of regulatory genes are present only in small numbers in other organisms. The genes controlled by these L. monocytogenes regulators is largely unknown; therefore, mutant strains carrying a single genetic mutation individually interrupting each regulator were assayed to determine if any of these mutants exhibited altered resistance to heat treatment at 60 deg C. Reduced heat resistance would indicate that the regulators or the genes they control are candidate targets for designing improvements in the efficacy of thermal processes for inactivation of L. monocytogenes in foods. The heat resistance of the mutants was not significantly different than the control indicating that these regulators are unlikely to be involved in the heat resistance of the organism, and as a result would not serve as targets for improving the thermal inactivation of L. monocytogenes.
Technical Abstract: A surprising facet of the L. monocytogenes genome is the presence of 15 genes in the Crp/Fnr regulatory family, and with the exception of PrfA, the gene networks controlled by these regulators are currently undetermined. Using single transposon mutants for 12 of the Crp/Fnr regulators of L. monocytogenes strain F2365, we heat challenged each strain at 60 deg C using an immersed-coil heating apparatus, modeled the survivor data to calculate the underlying mean and mode of the heat resistance distribution for each strain, and compared each mutant to the wild type strain to determine if any of the Crp/Fnr mutants demonstrated altered heat tolerance. All 12 of the Crp/Fnr mutant strains tested had heat resistance characteristics similar to the wild type strain (adjusted P > 0.05) indicating that mutations in these Crp/Fnr genes neither increased nor decreased the sensitivity of L. monocytogenes strain F2365 to mild heat.