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Egg white exposure induces membrane depolarization of Salmonella Enteritidis

Abstract : Salmonella enterica serovar Enteritidis is the major pathogen responsible for egg-borne infection in humans due to its exceptional ability to survive in egg white in contrast to other serovars and species. Comprehensive overview is needed regarding the mechanisms which enable Salmonella to survive in egg white despite the antimicrobial activities of this medium. It is generally accepted that the key anti-S. Enteritidis activities of egg white are iron deficiency and bacterial-cell membrane damages due to egg white antimicrobial proteins. However, the ability of S. Enteritidis to maintain cell-envelope integrity could take part in its resistance to egg white. The alkaline pH of egg white (rapid increase from 7.8 up to 9.3 in a few days after laying) was also highlighted in several studies as an anti-S. Enteritidis factor, given that the maintenance of intracellular pH around 7.8 is essential for many biological functions and for the status of cell membranes. Thus, an alkaline pH mainly affects the bacterial cells which must preserve the proton motive force and the electrochemical potential across their membranes. One of the objectives of this study was to investigate if incubation of S. Enteritidis in egg white results in the depolarization of the cell membrane. The role of egg white proteins and alkaline pH in such modifications was also assessed. Membrane depolarization was measured using a method adapted from Epand et al. (2010) based on fluorescence increase of DiSC3 dye when membrane depolarization occurs. In order to investigate the effect of egg white proteins, relative fluorescence intensity was measured on bacteria cells incubated either in egg white (around 10 g/L proteins, reference “100 %”), in egg white filtrate obtained using 10 kDa cut-off ultrafiltration membrane (“0 %” proteins), or in egg-white filtrate plus 10% egg white (“10%” proteins). In order to assess the role of egg white pH, the relative fluorescence intensity was also measured on cells incubated in “10%” egg white at pH 7.8 or 9.3. The results showed a significant increase of DiSC3 fluorescence when cells were incubated with “10%” and “100%” egg white proteins, unlike those incubated with “0%” proteins. No difference was observed between pH 7.8 and 9.3. Thus, egg white proteins are involved in the disruption of S. Enteritidis membrane potential and could participate in the bacteriostatic effect of egg white towards this serovar. On the contrary, the alkaline pH of egg white does not appear to be a key parameter.
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https://hal.inrae.fr/hal-02737918
Contributor : Migration Prodinra <>
Submitted on : Tuesday, June 2, 2020 - 8:01:47 PM
Last modification on : Thursday, March 18, 2021 - 11:44:09 AM

Identifiers

  • HAL Id : hal-02737918, version 1
  • PRODINRA : 493767

Citation

Marie-Françoise Cochet, Sylvie Bonnassie-Rouxin, Francoise Nau, Sophie Jan, Florence Baron. Egg white exposure induces membrane depolarization of Salmonella Enteritidis. Symposium Salmomella and Salmonellosis I3S 2018, Sep 2018, Saint MALO, France. 2018. ⟨hal-02737918⟩

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