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The Comparison of Strawberry Extract on the growth of two Different
Gram-negative Bacteria. Formatting
Mohammad Dadkhah, Amin Najmabadi
Department of Biology, Saddleback College, Mission Viejo, California
Abstract
Strawberry is a rich source of bioactive compounds, such as phenolics and organic
acids, which have antimicrobial activities properties against human pathogens. Their
antimicrobial activity has gained importance as phenolic berry extracts inhibit the growth
of selected Gram-negative intestinal bacteria. Two types of Gram-negative bacteria were
chosen for this experiment: Escherichia coli and Salmonella Typhimurium. Escherichia
coli are is a common type, of Gram-negative bacteria that can get into infect various food
items, like such as beef and vegetables. Salmonella Typhimurium is a gram negative
bacterium that causes systemic infections and typhoid fever in humans. The aim of the
present study was is [by using the term present study you are implying that it is current and therefore
you would use present tense and not past tense to describe it]
to determine the effects of strawberry
extract on selected pathogenic bacteria such as E. coli and S. Typhimurium [you can shorten
this one as well]
to identify antibacterial activity. One control group for E. coli, and 1 one
[use the same formatting for the entire paper so if you write a number out do not use the numerical symbol
for it also, besides it is far more professional to write it out; also employ the use of commas and avoid using
the word “and” so many times]
for Salmonella Typhimurium and as well as an experimental
group for each bacterium. 10ml of each bacteria were was obtained from the colonies
grown and were was placed on to the Petri dishes by a 0.25 lawn spread. Salmonella with
DI water 0.30mm  0.13mm [below you describe that there are four experimental setups however you
neglect to describe the measurements for Salmonella Strawberry, although you refer to it below]
. E.coli
with Strawberry had a zone of inhibition of 14.65mm  0.39mm and with DI water
0.25mm  0.11mm. We suggest that there is no significant difference when comparing
Salmonella Strawberry with Salmonella DI water but there is a significant difference when
comparing E.coli Strawberry with E.coli DI water. There is also a significant difference
when comparing Salmonella [remember to spell the subject of the study correctly and also to italicize
strawberry
it]
with
E.coli
Strawberry.
Introduction
Flavonoids are common substances in the daily diet. These polyphenolic
compounds are widely found in various types of edible plants, especially in vegetables,
fruits, tea and wine. Over 4000 different favonoids [make sure you spell things correctly] have
been described and they are categorized into several subgroups (Puupponen-Pimia et al.
2004). Flavanones are typically present in citrus fruit, and favanols [spell correctly] in green
tea. Berries, which are traditionally a part of the Finnish diet, are an excellent source good
sources of favonols [spell correctly] while the predominating predominant [use this form
instead]
group of favonoids [spell correctly], especially in red berries, is anthocyanins
(Puupponen-Pimia et al. 2004). Strawberry is a rich source of bioactive compounds, such
as phenolics and organic acids, which have antimicrobial activities against human
pathogens. [verbatim from above, okay to use but change activities to properties]
Berry phenolics possess many interesting biological activities properties. Their
antimicrobial activity has properties have gained importance as phenolic berry extracts
inhibit the growth of selected Gram-negative intestinal bacteria. Strawberries contain
ellagitannins or Ellagic acid and citric acid. Strawberry ellagitannins slow the growth of
abnormal colon cells in humans (Ulanowska et al2007). These ellagitannins protect
human cells against cancer-causing agents in tobacco smoke, food additives, and
petroleum-based substances. Ellagitannins act as scavengers to “bind” cancer-causing
chemicals, making them inactive. The ellagitannins inhibit the ability of other chemicals
to cause mutations in bacteria. Strawberry ellagitannins also protect DNA by blocking
carcinogens from binding to the DNA (Heinonen et al. 2000). Bacteria are a part of our
everyday life. Most are harmless, a few are beneficial, and some are harmful pathogens.
Pathogenic bacteria or toxins produced by bacteria often enter the human body via food
or drink causing symptoms or illness with several mechanisms. E. coli is a common type
of Gram-negative bacteria that can get into infect food, like beef and vegetables. E. coli is
short for the medical term Escherichia coli. E. coli normally lives inside your intestines,
where it helps your body break down and digest the food you eat. Unfortunately, certain
types (called strains) of E. coli can get from the intestines into the blood. This is a rare
illness, but it can cause a very serious infection. Salmonella Typhimurium is a gram
negative bacterium that causes systemic infections and typhoid fever in humans. This
rod-shaped, flagellated organism’s sole reservoir is humans. It has caused many deaths in
developing countries where sanitation is poor and is spread through contamination of
water and undercooked food. Bacteria adhere to and commonly penetrate through the
epithelium of the intestines. Most people recover from salmonellosis spontaneously, but
sometimes antibiotic treatments are needed. Studies on flavonoids have attracted a lot of
interest recently because they have a variety of beneficial biological properties such as
antioxidant and anti-cancer activities (Heinonen et al. 2000; Daniyan et al. 2008;
Ulanowska et al. 2007). The aim of the present study was is to determine the effects of
strawberry extract on selected pathogenic Gram-negative bacteria such as E. coli and
Salmonella Typhimurium to identify antibacterial activity. Such knowledge is important
for the development of health-promoting functional foods containing both probiotic
bacteria and plant material, such as berries.
Methods
Forty of nutrient agar plates were made on November 4, 2009. Using a mixture of
11.5g of nutrient agar powder with 500ml distilled water in two 2 Erlenmeyer flasks.
They were then placed in the autoclave for two hours at 120C. The solution was poured
into 40 Petri dishes and placed in the incubator at 37C for 24 hours. On November 5th
the plates were divided into four groups of ten. One control group for E. coli and one for
Salmonella Typhimurium and an experimental group for each bacterium. 10 ml of each
bacteria were was obtained from the colonies grown at in the Saddleback College
laboratory. The bacteria were placed on to the petri dishes by a 0.25 lawn spread. Eighty
7mm chads were punched from 2cm Whatman filter papers and were placed in a petri
dish and autoclaved. These sterilized chads were dipped into DI water and placed on the
control groups and for the experimental groups they were dipped into strawberry extract.
Fresh strawberry extract was made by squeezing fresh strawberries in the juicer in the
student research laboratory. The 40 petri dishes were then stored in the incubator at 37C
for four days. On Monday November 9th the zones of inhibition were measured in
millimeters using a millimeter ruler. Microsoft Excel was used to calculate the mean
value for each group and an ANOVA test was preformed. The ANOVA was verified
using the Bonferroni Correction Post Hoc test.
Results
16
14
12
10
8
6
4
2
0
Salmonella Strawberry
Salmonella DI water 1
E.coli Strawberry
E.coli DI water
Diffrent groups
Figure 1. Radius of zone of inhibition measured in Salmonella Typhimurium and
Escherichia coli with DI water vs. strawberry. Salmonella with strawberry had a mean
zone of inhibition of 0.45mm  0.16mm, Salmonella with DI water 0.30mm  0.13mm.
E.coli with Strawberry had a zone of inhibition of 14.65mm  0.39mm and with DI water
0.25mm  0.11mm. 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.
[be sure to make the font size under the figure smaller than the rest of the text]
A Post Hoc (Bonferroni Correction) analysis of the data suggests that there is no
significant difference when comparing Salmonella Strawberry with Salmonella DI water
but there is a significant difference when comparing E.coli Strawberry with E.coli DI
water. There is also a significant difference when comparing Salmonella strawberry with
E.coli Strawberry.
Discussion
The antibacterial effect of Strawberry extract was measured against two Gramnegative bacteria, Salmonella Typhimurium and Escherichia coli. The results of our study
show 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 because of phenolic
compounds in strawberry. Recent studies showed that phenolic compounds in strawberry
was 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 exhibited that phenolic compounds, especially ellagitannins
contained in strawberry was responsible for the strong antibacterial effects against the E.
coli bacteria. There was were no pH effects in the inhibition caused by the pure phenolic
fractions, because pH of the fractions was determined to be in the neutral area range. The
main organic acids present in most berries are include 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 does [incorrect word] not contains benzoic and malic acids
(Puupponen-Pimia et al. 2004). We would like to suggest that the reason of for the
growth of salmonella bacteria on experimental plates was because of due to the absence
of these organic acids in the strawberries, which is supported by our preliminary
experiments. However this has to be further confirmed.
References
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
Keiko Iwashita, Masuko Kobori, Kohji Yamaki, and Tojiro Tsushida, 2000, Flavonoids
Inhibit Cell Growth and Induce Apoptosis in B16 Melanoma 4A5 Cells. Biosci.
Biotechnol. Biochem 64(9), 1813-1820
R. Puupponen-PimiaÈ, L. Nohynek, C. Meier, M. KaÈhkoÈnen, M. Heinonen,
A. Hopia and K.-M. Oksman-Caldentey. 2001. Antimicrobial properties of phenolic
compounds from berries. Journal of Applied Microbiology 90: 494-507
R. Puupponen-Pimiä, L. Nohynek, S. Hartmann-Schmidlin. M. Kähkönen, M. Heinonen,
K. Määttä-Riihinen and K.-M. Oksman-Caldentey, 2004. Berry phenolics selectively
inhibit the growth of intestinal pathogens. Journal of Applied Microbiology 98: 991-1000
S. Y. Daniyan and H. B. Muhammad, 2008, Evaluation of antimicrobial activities
and
phytochemical properties of extracts of Tamaridus indica against some
diseases causing bacteria. African Journal of Biotechnology 2451-2453
Review Form
Department of Biological Sciences
Saddleback College, Mission Viejo, CA 92692
Author (s): Mohammad Dadkhah and Amin Najmabadi
Title:The Comparison of Strawberry Extract on the growth of two Different Gramnegative Bacteria.
Summary
Summarize the paper succinctly and dispassionately. Do not criticize here, just show that you understood the paper.
The experiment which was performed was of great educational value, and the results are
quite interesting. The use of strawberry extract as a bacterial growth inhibitor was a
unique choice. As well as all the background information as to why the researchers
selected strawberries as their growth inhibitor as opposed to another type of berry. The
execution of the experiment by using a control group with DI water was also a great idea
and the way in which they described the use of this makes the reader understand its,
importance. Overall I think the message of the paper is very interesting and informative
and the authors really do convey interesting results.
General Comments
Generally explain the paper’s strengths and weaknesses and whether they are serious, or important to our
current state of knowledge.
The paper’s weaknesses included several spelling errors throughout such as in the first
half of the introduction where “flavonoids” and all its derivatives were spelt incorrectly
numerous times. I consider these issues to be quite serious especially at the level at which
we are operating.
The title is also weak and I would suggest changing it to something such as “The Effect
of Strawberry Extract on the Growth of Gram-Negative Bacteria” as this encompasses the
research that was performed however it doesn’t limit the scope of the research either.
As far as the strengths go, the use of outside references was good, as well as the overall
description of the experiment itself. In addition to this the background information
utilized throughout the paper was also very good as it gives the reader a broader scope of
the way in which this research is important.
Technical Criticism
Review technical issues, organization and clarity. Provide a table of typographical errors, grammatical
errors, and minor textual problems. It's not the reviewer's job to copy Edit the paper, mark the
manuscript.
This paper was a final version
This paper was a rough draft
I thought the organization of the paper was very good and I thought it flowed very
well. Also the message that the authors were trying to convey seems quite clear.
All errors have been highlighted in red so the authors may correct them. The
majority of the errors were spelling errors with a few errors in regards to tense as
well as some grammatical errors.
Also the authors would be wise to take a look through the past Saddleback
College Journal to familiarize themselves with the format of their names, as well
as the address of the institution and how it should be presented within the paper.