Eight foodborne pathogenic and spoilage Gram-positive bacteria were
evaluated for their spontaneous resistance frequencies to the peptide
antimicrobial nisin. In brain heart infusion (BHI) medium, nisin resistance
frequencies were in the range of l06 to l08 when exposed to nisin at
concentrations 2 to 4 times the minimal inhibitory concentrations.
A stable nisin resistant mutant of Listeria monocytogenes Scott A was
obtained by increasing stepwise exposure to nisin and subsequently
characterized. Phospholipid content, fatty acid composition, phase transition
temperature (Tc), and specific growth rates of the resistant mutant and parent
were determined. The Tc of the resistant mutant (44.4°C) in comparison of
the parent (37.4°C) indicated that significant changes occurred in the lipid
composition of the mutant. Gas chromatographic analysis of fatty acids of
mutant and parent revealed significant differences (P<0.05) in the
proportional ratios of fatty acids; 14:0, 15:0 iso, 15:0 anteiso and 17:0 iso. cells and the concentration of nisin required for reaching a 50% maximum
killing rate was five times that of sensitive cells. The bactericidal activity of
nisin was more effective at 37°C than 4°C for both resistant and sensitive cells,
but there was always higher survival of resistant cell than sensitive cells for
both temperatures. Nisin degradation and plasmid involvement were
demonstrated to not be the responsible resistance mechanism to nisin in
L. monocytogenes. No cross-resistance was observed to therapeutically
important antibiotics (rifampicin, chloramphenicol, vancomycin,
erythromycin) and to metabolic inhibitors (CCCp, DCCD) by the nisin-resistant
mutant. / Graduation date: 1993
| Identifer | oai:union.ndltd.org:ORGSU/oai:ir.library.oregonstate.edu:1957/27088 |
| Date | 09 April 1993 |
| Creators | Ming, Xintian |
| Contributors | Daeschel, Mark A. |
| Source Sets | Oregon State University |
| Language | en_US |
| Detected Language | English |
| Type | Thesis/Dissertation |
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