Volume 6, Spring 2008 - Saddleback College

Fall 2007 Biology 3A Abstracts
understanding of using silver nitrate (AgNO 3 ) to
inhibit the growth of the bacteria Escherichia coli.
An article published by Nataro and Kaper (1998) in
the Clinical Microbiology Reviews, Escherichia coli
is the predominant nonpathogenic facultative flora of
the human intestine. Some E. coli strains, however,
have developed the ability to cause disease of the
gastrointestinal, urinary, or central nervous system in
even the most robust human hosts. This makes quite a
challenge in the inhibiting treatment of E. coli.
According to Feng and Wu (2000) on the
antibacterial effect of silver ions on E. coli and
Staphylococcus aureus after the use of silver ions
there were morphological changes in both bacteria.
Silver is an agent known to have antibacterial
properties and its inhibiting effect on E. coli would
be a very cost effective way to treat outbreaks of this
bacteria. Investigators Sondi and Sondi (2004) at the
Center for Marine and Environmental Research
found that nanosized silver particles damaged E. coli
cells, showing formation of “pits” in the cell wall of
the bacteria, while the silver nanoparticles were
found to accumulate in the bacterial membrane. A
membrane with such morphology exhibits a
significant increase in permeability, resulting in the
death of the cell. Schreurs and Rosenberg (1982)
concluded that silver ions inhibit the respiratory chain
of E. coli possibly at two sites of different
sensitivities, and were also reported, in the journal of
bacteriology, to exert an uncoupler-like action. It
seems that silver will affect the E. coli in some way
most often damaging the replication process and
contributing to the death of the cell. Rosenkranz and
Carr found that silver sulfadiazine blocked
macromolecular synthesis in treated bacteria. Silver
has been a known antibacterial agent against gram
negative bacteria and could also have an effect on the
gram positive bacteria E. coli. Gram positive bacteria
is very resistant to antibiotic treatment. According to
Jack and Tagg (1995) the journal of microbiology
and molecular biology reviews published an article
on the bacteriocins of gram positive bacteria and
stated that the antibacterial action against a sensitive
cell of a gram-positive strain is produced principally
by destabilization of membrane functions. Silver
nitrate is a chemical agent with properties that may
demobilize the growth of E. coli. The hypothesis for
this experiment is that the agar with the highest
concentration of Silver Nitrate will have the greatest
effects on inhibiting the growth of Escherichia coli.
We anticipate the inability for the E. coli eukaryotic
cells to replicate with the treatment of silver nitrate.
department were used to prepare an agar solution
within 500mL of water to determine the inhibition
growth of Escherichia coli. The agar solution was
introduced to fifteen petri dishes all correctly labeled
to the amount of silver nitrate they were introduced to
(0%, 0.5%, and 1.0%). After the agar solution
hardened, 0.5mL of Escherichia coli were pipetted
with a P1000 micro pipette onto each plate and
spread with a sterile glass rod to form a lawn. The
glass rod was dipped into ethanol, flamed, and cooled
in between each plate. Following the incorporation of
E. coli silver nitrate was placed in both the 0.5% and
1.0% labeled plates. The 0% sample was used as a
control group and left without silver nitrate.
A 1.0% silver nitrate solution was obtained
and used to make a 0.5% silver nitrate solution by
diluting 1.0mL of it into 1.0mL of water. Chads were
used to incorporate the corresponding silver nitrate
solution into the correctly labeled petri dish. There
were a total of four chads placed across from each
other into each dish. The same procedure was
followed for the remaining concentrations. Before
placing a chad in each plate forceps were sterilized
by dipping them into ethanol, placing them over a
flame, and letting them cooled in between each plate.
This process was strictly followed in order to avoid
any possible contamination that could interfere with
the case being studied. All petri dishes were placed
into a 37°C incubator and results were interpreted
within a 48 hour period. After each 48 hour period
silver nitrate formed a perimeter of inhibition around
each chad. The perimeter formed was measured in
millimeters and used to determine the inhibition
growth of E. coli.
Results
Materials and Methods
Ten grams of nutrient agar obtained from
the Saddleback College Biological Science
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Saddleback Journal of Biology
Spring 2008