Wspólnotowy Serwis Informacyjny Badan i Rozwoju - CORDIS

Anti-listerial yeast

Anti-listerial yeasts:
A screening method to test for anti-listerial activity in yeast was developed by Partner 7. The reproducibility of this method was confirmed by investigations done by Partners 1, 2, 3 and 7. As a test set 5 inhibitory and 5 non-inhibitory yeasts from previous investigations of Partner 7 and three strains each from Livarot, Tilsit, Gubbeen and Limburger cheese were chosen. The inhibitory potential of these 22 yeast strains was tested against six Listeria monocytogenes strains, WSLC 1001, 1364, 1685, 1416, 1211 and 1039. The anti-listerial activity was evaluated using a score-based system developed by Partner 7. Yeast strains with a strong and moderate anti-listerial activity retained this property.

The order of the scores of all four partners were similar and Listeria strains showed differences in sensitivity. Under the best inhibitory yeasts were the top five yeasts from previous experiments done by Partner 7, followed by yeasts isolated from Livarot and Tilsit cheese. According to the results of the four partners the method was considered to be reproducible and reliable. Further screenings of yeasts from the different project cheeses were done by the individual partners. A total of 58 yeasts out of 1944 tested inhibited at least for of the selected L. monocytogenes indicator strains used in these investigations.

Afterwards Partners 1, 2, 3 and 8 validated inhibitory yeasts by different methods. Partner 2 tested the 5 inhibitory yeasts from Partner 7 as well as 5 inhibitory yeasts from Tilsit against two L. monocytogenes indicator strains using a cheese agar. A clear inhibition was observed compared to the control. The other three partners used cheeses for their validation. The results obtained were different. Partner 1 observed inhibition at some time points but not at others. Investigations done in two replicates were not reproducible. Partner 3 obtained inhibition with some yeasts. Differences in individual experiments were most likely due to the concentrations of yeasts used. One yeasts was tested in detail but no inhibition was obtained. In investigations on cheeses of Partner 8 Listeria grew to a lesser extend with highly inhibitory yeasts than with less inhibitory yeasts.

Possible explanations for the differences between the results on cheese agar and cheese were the level of yeasts used, the time of addition of Listeria and yeast, the contact between bacteria and yeast, the porosity of the cheese surface and the interactions between other surface microorganisms.

Reported by

Weihenstephaner Berg 3
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