Glycine and its N-methylated analogues cause pH-dependent membrane damage to enterotoxigenic Escherichia coli
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The current study first investigates the emulsifying potential of glycine and its N-methylated derivatives N-methylglycine (sarcosine), N,N-dimethylglycine (DMG) and N,N,N-trimethylglycine (betaine) under varying pH conditions. Subsequently, the effect of these test compounds on the membrane integrity of enterotoxigenic Escherichia coli (ETEC) was evaluated. Oil in water emulsions containing each compound show that DMG is a more potent enhancer of emulsification than glycine, sarcosine and betaine under the conditions tested. Flow cytometry was used to investigate whether the emulsifying potential is associated with an effect on ETEC membrane integrity. The bacteria were exposed to each of the test compounds under varying pH conditions and membrane integrity was assessed using the LIVE/DEAD BacLight kit. Results show a membrane deteriorating effect caused by glycine, sarcosine and DMG, but not by betaine. This effect is pH- and time-dependent and has an apparent threshold at pH 9.0. Conventional plate counts confirmed concomitant changes in culturability of the membrane comprised bacteria.
KeywordsGlycine Methylamine Flow cytometry Membrane integrity Emulsification Alkaline stress
The present study was funded by Taminco NV (Belgium). The authors’ responsibilities were as follows D. Vanhauteghem conducted the experiments and collected all data, except for the MIC data which were collected by F. Boyen. S. Sys performed statistical analysis and D. Vanhauteghem wrote the manuscript. E. Meyer., I.D. Kalmar, A. Lauwaerts, S. Sys and G.P.J. Janssens revised the manuscript. E. Meyer and G.P.J. Janssens supervised D. Vanhauteghem.
Conflict of interest
The authors declare that they have no conflict of interest.
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