T2-07 Acid Adaptation Enhances Salmonella Enteritidis Acid and Heat Resistance Due to the Decreased Membrane Fluidity But Not Upregulation of the Stress Related Genes

Monday, August 4, 2014: 10:30 AM
Room 203-204 (Indiana Convention Center)
Yishan Yang, National University of Singapore, Singapore, Singapore
Mellissa Irlianti Kadim, National University of Singapore, Singapore, Singapore
Wei Jie Khoo, National University of Singapore, Singapore, Singapore
Hyun-Jung Chung, Inha University, Incheon, South Korea
Hyun-Gyun Yuk, National University of Singapore, Singapore, Singapore
Introduction: Salmonella Enteritidis is one of the most common causes of human salmonellosis reported worldwide. Antimicrobials, like lactic acid (LA) and trisodium phosphate (TSP), have been approved to reduce foodborne pathogens in animal carcasses. However, adaptation to the sublethal concentration of these antimicrobials may render pathogens greater resistance towards lethal conditions and become more virulent.

Purpose: This study aimed to investigate whether acid or alkaline adaptation alters Salmonella acid/heat resistance and virulence gene expression, as well as, to find out whether the alternation in Salmonella resistance was due to the changes in membrane lipid composition/expression of stress-related genes or both of them. 

Methods: S. Enteritidis was cultivated at different pHs (5.3-9.0) adjusted by LA or TSP. Adapted cells were subject to simulated gastric fluid (pH=2.0) and thermal treatment (54, 56, 58, and 60 °C) to determine its acid/heat resistance. D-values were calculated based on survivor curves. Membrane lipid composition was determined by gas chromatography. The transcription levels of stress-related genes (rpoS and rpoH) and virulence-related genes (spvR, hilA, sefA, and avrA) were evaluated by real-time PCR. Mean values were compared using ANOVA.

Results: Results showed that cells adapted at pH 5.3 had significantly (P < 0.05) higher acid (D-value = 7.9 min) and heat resistance (D60oC-values = 0.87 min), followed by the control and alkali-adapted cells. The increased resistance was correlated with the decreased membrane fluidity; whereas no upregulation of rpoS and rpoH was found in acid-adapted cells. About 6.0, 2.1, and 2.5-fold upregulation of spvR, avrA, and hilA were observed in cells adapted to pH 9.0, whereas sefA had its highest expression level in the control cells. 

Significance: This study indicates that the regulation of the cytoplasmic membrane rather than the stress-related genes may play a more crucial role in conferring acid and heat resistance on acid adapted S. Enteritidis.