Saddleback Journal of Biology - Saddleback College

Fall 2009 Biology 3B Paper
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Salmonella Strawberry Salmonella DI water 1 E.coli Strawberry E.coli DI water
Diffrent groups
Figure 1. Diameter of zone of inhibition measured in Salmonella typhimurium and Escherichia coli with DI water
vs. strawberry. The result suggests that there is a significant difference when comparing E.coli Strawberry with any
of the other groups. (p=1.07 x 10 -34 , ANOVA). Errors bars are SEM.
Discussion
The antibacterial effect of Strawberry was
measured against two Gram-negative bacteria,
Salmonella typhimurium and Escherichia coli. The
results of our study shows that Strawberry has a
different effect on different Gram-negative bacteria.
Strawberry extract inhibited the growth of E. coli but
not Salmonella. Phenolic extracts of strawberry
disintegrated the outer membrane of examined E. coli.
Recent studies showed that phenolic compounds in
strawberry were not effective on Salmonella
typhimurium bacteria growth and most of the
inhibition seemed to originate from other compounds,
such as organic acids which is not available in
strawberry extract (Puupponen-Pimia et al. 2004).
Result shows that strawberry extracts clearly showed
that phenolic compounds, especially ellagitannins
contain in strawberry were responsible for the strong
antibacterial effects against the E. coli bacteria. There
was no pH effects in the inhibition caused by the pure
phenolic fractions, because pH of the fractions was in
neutral area. Main organic acids present in most
berries are benzoic acid, citric acid and malic acid
(Ulanowska et al. 2007). In their undissociated state
(in pH below the pKa value of the acid) the acids may
function as permeabilizers of the Gram-negative
bacteria outer membrane and may act as potentiator of
the effects of other antimicrobial substances. However
Strawberry dose not contains benzoic and malic acids
since it is not a true berry (Puupponen-Pimia et al.
2004). We would like to suggest that the reason of
growth of salmonella bacteria on experimental plates
was because of absence of these organic acids in the
strawberries, which is supported by our preliminary
experiments. However this has to be further
confirmed.
Acknowledgments
Investigators would like to thank Professor
Steve Teh, for his knowledge and help with the
experiment and Aaron Ko for helping with writing the
paper. They would also like to thank the Biological
Science department for the equipment used in the
experiment.
Literature Cited
Katarzyna Ulanowska, Anna Majchrzyk1, Marta
Moskot, Joanna Jakóbkiewicz-Banecka3 & Grzegorz
W. 2007. Assessment of antibacterial effects of
flavonoids by estimation of generation times in liquid
bacterial cultures. Department of Molecular Biology,
University of Gda´nsk. 2: 132—135
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Saddleback Journal of Biology
Spring 2010