Influence of autoinducer 2 (AI-2) and AI-2 inhibitors generated from processed poultry on virulence and growth of Salmonella enterica serovar Typhimurium
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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.
Widmer, Kenneth Walter (2007). Influence of autoinducer 2 (AI-2) and AI-2 inhibitors generated from processed poultry on virulence and growth of Salmonella enterica serovar Typhimurium. Doctoral dissertation, Texas A&M University. Available electronically from