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Influence of autoinducer 2 (AI-2) and AI-2 inhibitors generated from processed poultry on virulence and growth of Salmonella enterica serovar Typhimurium

Bacteria produce and respond to external stimuli using molecules termed
autoinducers. Poultry meat contains inhibitors which interfere with AI-2
signaling. The primary objective of this work was to understand the effects of
AI-2 on the virulence and growth of Salmonella Typhimurium, and if the
introduction of AI-2 inhibiting compounds would influence these effects.
Using DNA microarray analysis, expression of 1136 virulence-related
genes in a Salmonella Typhimurium wild type and a luxS mutant strain, PJ002
(unable to produce AI-2), was monitored after exposure to treatments
containing in vitro synthesized AI-2 (AI-2) and poultry meat (PM) inhibitors.
Responding gene expression was unique in the presence of AI-2, with 23 genes
differentially expressed at least 1.5-fold (p < 0.05). The combined AI-2 + PM
treatment resulted in 22 genes being differentially expressed. Identification of
inhibitory compounds was attempted using GC analysis on a hexane solvent
extract obtained from a PM wash. From this analysis, chemical standards of linoleic, oleic, palmitic, and stearic acid were tested for inhibition using V.
harveyi BB170. Combined fatty acids (FA) demonstrated inhibition against AI-2
at 60 % while 10-fold and 100-fold concentrations had inhibition of 84 % and 70
%, respectively. Growth of PJoo2, was studied using M-9 minimal medium with
FA of varying concentrations, supplemented with either AI-2, or 1X phosphate
buffered saline (PBS). Comparative analysis was done calculating the growth
constants based on OD 600 values for each treatment. No significant difference
in the combined FA + AI-2 treatments was observed against the AI-2 treatment.
A significant increase in the growth rate constants of the AI-2 treatments was
observed, however, compared to the PBS control (P = 0.01). Bacterial
invasiveness, using a murine macrophage cell line, RAW 264.7, was also studied.
AI-2 decreased cell invasiveness (P = 0.02), while the addition of combined FA
improved invasiveness to normal levels. The results of these studies indicate
that AI-2 does have an effect on the growth and virulence of Salmonella, but this
is not uniformly modulated by the introduction of fatty acids, that inhibit AI-2
activity, suggesting that inhibition may be based on species specific transport
systems.

Identiferoai:union.ndltd.org:tamu.edu/oai:repository.tamu.edu:1969.1/ETD-TAMU-1313
Date15 May 2009
CreatorsWidmer, Kenneth Walter
ContributorsPillai, Suresh D.
Source SetsTexas A and M University
Languageen_US
Detected LanguageEnglish
TypeBook, Thesis, Electronic Dissertation, text
Formatelectronic, application/pdf, born digital

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