Effect of Cultivation Conditions on the Yeast-Induced Flocculation of Escherichia coli

Xuan Peng, Dirk Iserentant*, Hubert Verachtert

Laboratory for Industrial Microbiology and Biochemistry, K. U. Leuven, Kardinaal Mercierlaan 92, B-3001 Heverlee, Belgium

Article history:
Received September 10, 1997
Accepted November 28, 1997

Key words:
Escherichia coli, Saccharomyces cerevisiae, fimbriae, yeast-bacterium interaction, diarrhea

Summary:
In humans, as well as in animals, Saccharomyccs cerevisiae can be used to treat diarrhea caused by Escherichia coli. However, the antagonistic effect of the yeast on E. coli is still not fully understood. In order to elucidate the mechanism, the yeast-induced flocculation of both the nonfimbriated E. coli strain XLl Blue and the fimbriated strain 4350, isolated from the faeces of a cow with diarrhea, was studied. Both strains flocculate in the supernatant of liquid cultures of a Sacch. cerevisiae strain that is used in antidiarrhea treatment. Presumably, this flocculation is induced by a glycoprotein released by the yeast in the culture medium during fermentation. This glycoprotein may link the E. coli cells together by a lectin type of binding. The yeast-induced flocculation of the bacteria is dependent upon their cultivation conditions. For both E. coli strains, cells harvested at different cultivation stages showed a different flocculation response in the yeast supernatant. Stationary phase cells are less flocculent than cells from the logarithmic growth phase. The flocculation assay, presented here, will be used to study the mechanism of the Sacch. cerevisiae - E. coli interaction in more detail.

*Corresponding author:          dirk.iserentant@agr.kuleuven.ac.be
                                               (32) 9-244 6610
                                               (32) 9-244 6611