Comparison of Real Time Polymerase Chain Reaction Quantification of Changes in hilA and rpoS Gene Expression of a Salmonella Typhimurium Poultry Isolate Grown at Fast Versus Slow Dilution Rates in an Anaerobic Continuous Culture System

Abstract

The objective of this study was to determine the genetic responses of a Salmonella enterica Typhimurium poultry isolate during low and high dilution rates (D) in steady state continuous culture (CC) incubations. Samples for genetic analyses were taken from a previous study where S. Typhimurium cells had been grown in two chemostats operated concurrently, which were designated as Trials 1 and 2, with eight dilution rates sampled during steady state. Real-time polymerase chain reaction (PCR) on two target genes (rpoS and hilA) was analyzed as changes in expression of the target gene relative to the reference gene (16S rRNA). At the lowest D (0.0125 h⁻¹) in Trial 2, rpoS expression was more than twofold higher than the second highest relative expression. In Trial 1 hilA expression was 21.8-, 27.8-, and 21-fold higher in D 0.0125 h⁻¹, 0.025 h⁻¹, 0.05 h⁻¹, respectively, compared to D 0.1 h⁻¹, 0.54 h⁻¹, and 1.08 h⁻¹. In Trial 2, D 0.025 h⁻¹ and 0.27 h⁻¹ showed no difference in hilA expression but were significantly higher compared to other D. From these results, low glucose conditions may play an essential role in triggering rpoS induction, as well as contributing to potential virulence.

Keywords:

• Salmonella Typhimurium
• hilA
• rpoS
• continuous culture

ACKNOWLEDGMENTS

These studies were conducted with funds from USDA-NRI Grant #2001-02675 administered by Texas Agricultural Experimental Station. Thanks to Cassie Woodward and Dr. W. K. Kim for data analysis and helpful discussion for preparation of the manuscript.