Degree Type

Dissertation

Date of Award

2006

Degree Name

Doctor of Philosophy

Department

Food Science and Human Nutrition

First Advisor

Aubrey F. Mendonca

Abstract

Listeria monocytogenes is a ubiquitous, pathogenic foodborne bacterium, typically associated with post-processing contamination of ready-to-eat meats. Control of this pathogen has been a research topic for years, with more recent work investigating the use of novel naturally-produced antimicrobials. Methanobactin is a novel, chromopeptide recently isolated from the methanotroph, Methylosinus trichosporium OB3b. Its recent characterization has placed it in a new class of compounds now known as chalkophores, which are analogous to iron-binding siderophores. While it is thought to possibly serve multiple physiological roles involving copper metabolism in this bacterium, nothing is known regarding its potential as an antimicrobial. Our research focused on the use of copper-bound methanobactin (Mb-Cu) to control L. monocytogenes, thus the objectives of our studies were: (1) Determine the minimum inhibitory concentration (MIC) of Mb-Cu, at different pH values, and its effect on cell viability. (2) Optimize Mb-Cu activity by combining it with various surfactants. (3) Evaluate the anti-listerial efficacy of Mb-Cu, sodium lauryl sulfate (SLS), and their combination as surface treatments on frankfurters formulated with and without sodium lactate (NaL). (4) Gather preliminary evidence regarding the potential mode of action of Mb-Cu against L. monocytogenes. At pH 5.5 to 7.3, the MIC (4.11 mM) of Mb-Cu was lowest at pH 6.0, while the bactericidal action at the MICs ranged from 3.34- to 4.87-log reductions of the pathogen. Combination with Tween 20 or 80 lowered Mb-Cu activity while SLS enhanced it, which lowered the MIC from 2.06 to 1.03 mM. At pH 5.75, SLS (0.25%) + 1.03 mM Mb-Cu reduced L. monocytogenes populations by 5.33-log cycles, whereas 2-fold higher concentrations of Mb-Cu alone were required to achieve this same reduction. On frankfurters after 24-h storage, 1% SLS + 10 mM Mb-Cu reduced L. monocytogenes by 1.91-2.66 log-cycles, extended the lag phase in the presence of NaL, and prevented counts from exceeding initial populations during storage at 4°C. In buffer, Mb-Cu reduced L. monocytogenes and inhibited respiration in a dose-dependent manner. Some leakage of UV-absorbing material was detected without cell lysis. Evidence points to the cell membrane as the potential biological target of Mb-Cu against L. monocytogenes.

DOI

https://doi.org/10.31274/rtd-180813-11479

Publisher

Digital Repository @ Iowa State University, http://lib.dr.iastate.edu

Copyright Owner

Clinton Lewis Johnson

Language

en

Proquest ID

AAI3229088

File Format

application/pdf

File Size

203 pages

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