title: Membrane lipid composition and stress/virulence related gene expression of Salmonella Enteritidis cells adapted to lactic acid and trisodium phosphate and their resistance to lethal heat and acid stress.
abstract: This study evaluated the acid and heat resistance of Salmonella Enteritidis in simulated gastric fluid (pH 2.0) and during thermal treatment (54-60 °C), respectively, after adaptation to lactic acid (LA) or trisodium phosphate (TSP) at various pHs (pH 5.3-9.0). The changes in membrane lipid composition and expression levels of RpoS and RpoH were examined to elucidate their roles in bacterial stress resistance. Transcriptional profile of several virulence-related genes was also analyzed. Results showed that LA-adapted cells at pH 5.3 and 6.3 had higher acid and heat resistance than control cells and cells adapted to TSP at pH 8.3 and 9.0. LA-adapted cells had the lowest ratio of unsaturated to saturated fatty acids, indicating that they might possess a less fluid membrane. It was observed that the expression levels of RpoH and RpoS were upregulated in TSP-adapted cells but not in LA-adapted cells. Thus, these results indicate that the increased acid and heat resistance of LA-adapted S. Enteritidis was possibly due to the decreased membrane fluidity instead of the upregulation of RpoS and RpoH. About 6.0, 2.1, and 2.46-fold upregulation of spvR, avrA, and hilA were observed in cells adapted to TSP at pH 9.0, except sefA that had its highest expression level in the control cells, indicating that the expression of these virulence genes highly depends on environmental conditions. This is the first study to show that the alteration in the cytoplasmic membrane rather than RpoS and RpoH plays a more crucial role in conferring greater acid and heat resistance on LA-adapted S. Enteritidis, thus providing a better understanding on the bacterial stress response to acidic conditions.
authors.affiliation: Food Science & Technology Programme, Department of Chemistry, National University of Singapore, Science Drive 4, Singapore 117543, Singapore.
authors.forename: Yishan
authors.initials: Y
authors.lastname: Yang
authors.affiliation: Food Science & Technology Programme, Department of Chemistry, National University of Singapore, Science Drive 4, Singapore 117543, Singapore.
authors.forename: Mellissa Irlianti
authors.initials: MI
authors.lastname: Kadim
authors.affiliation: Food Science & Technology Programme, Department of Chemistry, National University of Singapore, Science Drive 4, Singapore 117543, Singapore.
authors.forename: Wei Jie
authors.initials: WJ
authors.lastname: Khoo
authors.affiliation: Food Science & Technology Programme, Department of Chemistry, National University of Singapore, Science Drive 4, Singapore 117543, Singapore.
authors.forename: Qianwang
authors.initials: Q
authors.lastname: Zheng
authors.affiliation: Department of Chemical and Biomolecular Engineering, National University of Singapore, 4 Engineering Drive 4, Singapore 117576, Singapore.
authors.forename: Magdiel Inggrid
authors.initials: MI
authors.lastname: Setyawati
authors.affiliation: Department of Food Science and Biotechnology, Kyungnam University, Changwon 631-701, Republic of Korea.
authors.forename: Yu-Jin
authors.initials: YJ
authors.lastname: Shin
authors.affiliation: Department of Food Science and Biotechnology, Kyungnam University, Changwon 631-701, Republic of Korea.
authors.forename: Seung-Cheol
authors.initials: SC
authors.lastname: Lee
authors.affiliation: Food Science & Technology Programme, Department of Chemistry, National University of Singapore, Science Drive 4, Singapore 117543, Singapore; National University of Singapore (Suzhou) Research Institute, No. 377 Linquan Street, Suzhou Industrial Park, Suzhou, Jiangsu 215123, China. Electronic address: chmyukhg@nus.edu.sg.
authors.forename: Hyun-Gyun
authors.initials: HG
authors.lastname: Yuk
mesh_terms: D000222:Adaptation, Physiological / Q000235:genetics; D005227:Fatty Acids / Q000032:analysis; D020869:Gene Expression Profiling; D015964:Gene Expression Regulation, Bacterial; D006358:Hot Temperature; D006863:Hydrogen-Ion Concentration; D019344:Lactic Acid / Q000494:pharmacology; D008560:Membrane Fluidity / Q000235:genetics; D008563:Membrane Lipids / Q000737:chemistry*; D010710:Phosphates / Q000494:pharmacology; D012477:Salmonella enteritidis / Q000187:drug effects / Q000235:genetics / Q000254:growth & development / Q000502:physiology*; D013312:Stress, Physiological / Q000235:genetics; D014774:Virulence / Q000235:genetics*
chemical_list: D005227:Fatty Acids; D008563:Membrane Lipids; D010710:Phosphates; D019344:Lactic Acid; C018279:sodium phosphate
keywords: Acid adaptation; Alkali adaptation; Gene expression; Membrane lipid composition; Salmonella Enteritidis; Stress resistance