The Effects of Ampicillin Concentration on E. Coli Growth
Introduction
Results
Bacteria are unicellular organisms that are classified as prokaryotic, meaning
they do not have membrane-bound nuclei or organelles
E.coli, scientifically known as Escherichia Coli is a potentially pathogenic
bacterium. Pathogenic E.coli causes gastrointestinal symptoms. E.coli is one
of the main food-borne pathogens affecting both human and animal health.
With over 300 million people contracting the illness a year, it is vital to
understand whether this pathogen can be killed, resulting in treatment
through the usage of an anti-biotic such as Ampicillin. Ampicillin is an
antibiotic belonging to the penicillin family, a category of ß-lactams. The
amino acid group in the Ampicillin allows the antibiotic to penetrate the outermost membrane of the bacteria. Upon penetration, it acts as an inhibitor of
transpeptidase, an enzyme vital for cell wall synthesis, the lack of which
causes the bacterium to undergo lysis.4
Fig. 2
Mg/mL
Trial 1
(ZOI(mm))
Trial 2
(ZOI(mm))
0
0
0
5
32
38
3
The aim of this experiment was to determine the effects of Ampicillin
concentration on bacterial E.coli growth by observing the zone of inhibition
(ZOI).
The ZOI is the area around the Ampicillin sample which is uninhabitable by
E.coli.
Discussion
10
40
32
Before the conduction of this experiment, it was predicted that as the
concentration of Ampicillin increased, the growth of E.coli would decrease.
Therefore, measuring the ZOI allows the determination of the effect of
Ampicillin concentration on E.coli growth.
Fig. 2
By observing the results given by the Table (fig.2) and the graph (fig.3), the ZOI can be seen to between 3240mm. As the concentration of Ampicillin increased, the average ZOI also increased by 1mm. Therefore, it
can be determined that as the concentration of Ampicillin increases, the ZOI also increases. An increased
ZOI indicates that an increased amount of E.coli growth is inhibited. The lowest ZOI was from the lowest
concentration, 0mg/mL . The highest average ZOI was from the highest concentration, 10mg/mL. The
difference between the lowest and the highest was drastic with 0mg/mL producing an average ZOI of 0mm,
whereas the 10mg/mL produced an average ZOI of 36mm.
Independent variable: Concentration of Ampicillin (Anti-biotic) mg/mL
Dependent Variable: The Zone of Inhibition, indicating E.coli growth.
Data Trends: As shown by Fig. 3 and Fig. 2, the larger the concentration
of Ampicillin, the greater the size of the Zone of Inhibition, decreasing
E.coli growth.
The hypothesis of this experiment was proven to be correct which stated
that as the concentration of Ampicillin increases, the zone of inhibition
will increase, inhibiting E.coli growth since more Ampicillin will be able to
diffuse into the Agar, resulting in a larger spread.
Whilst the data results given by the trials of this experiment did generally
support the hypothesis, a result was outputted that did not follow the
hypothesis. Trial 2 of the 10mg/mL concentration of Ampicillin resulted in
the production of a 32mm ZOI. This value was the same as the average
ZOI of the 5mg/mL concentration. This result also differed from the first
trial of the 10mg/mL concentration which produced a ZOI of 40mm.
The experiment is unreliable due to the presence of an outlier. This
outlier could have been produced due to errors that occurred during the
conduction of this experiment. Reliability could have been improved by
increasing the number of trials. A greater number of trials would have
decreased the significant skew a single outlier had on the data set.
Systematic measurement errors could have occurred during the
measurement of the ZOI, this would result in the belief that a specific
Ampicillin concentration worked more or less than it did. Other sources
of error include atmospheric bacteria which could have landed on the
Agar. These bacteria may have a significant effect on the effectiveness on
a given Ampicillin concentration.
This experiment could be improved by repeating the experiment and
obtaining more data.
Aim, Variables, Hypothesis
The aim of the experiment was to determine the effect of Ampicillin
concentration on the growth of E.coli.
The independent variable for this experiment was the concentration of
Ampicillin and the dependent variable was the size of the zone of inhibition
It can be hypothesized that as the concentration of Ampicillin increases, the
zone of inhibition will also increase. This is due to the fact that an increased
concentration of Ampicillin is expected to diffuse into the Agar, resulting in a
larger spread, therefore increasing the zone of inhibition. It can also be
hypothesized that the 0mg/mL concentration of Ampicillin will produce no
zone of inhibition as there is no substance preventing bacterial growth.
Methodology and Safety
Conclusion
1. Set up a Bunsen burner station. Perform all bacterial work within about 30 cm of the Bunsen burner. The
updraft created by the flame creates a working zone that reduces the chance of contaminants falling onto your
agar plate.
2. Label the bottom of a nutrient agar plate with your initials, date, bacterial species and assigned concentration
of ampicillin.
3. Spread a bacterial lawn (refer to figure. 3). Dip the sterile swab into the bacterial broth and spread it uniformly
over the surface of the agar, rotate the plate as you spread and go to the edges of the agar surface.
4. Dip the forceps into a small volume of ethanol and pass its tips through the Bunsen burner flame to sterilise
it.
5. Using forceps carefully pick up a single sterile paper disc and dip it into your assigned concentration of
ampicillin. (0mg/mL, 5mg/mL, 10mg/mL).
6. Place disc onto centre of agar plate
7. Repeat for another agar plate
8. Tape lid on plate.
9. Place in a 30-37C̊ incubator, at least overnight
In conclusion, the aim of this experiment to investigate the effect of Ampicillin concentration on the growth
of E.coli was achieved. As seen in the results in Fig. 2 and Fig. 3, a general trend that the increase of
Ampicillin concentration will result in an increased ZOI, resulting in a decreased amount of E.coli growth.
These results support the hypothesis. While the experiment is valid, the reliability of the experiment is
uncertain due to a small data set which is then skewed by an outlier in the dataset. Similarly, systematic
errors may also lie in the experiment such as measurement errors of the ZOI.
References
1. Ampicillin(Penbritin). (2018, July 6). Retrieved 23 March 2022, from Netdoctor website:
http://www.netdoctor.co.uk/medicines/infections/news/a7323/penbritin-ampicillin/
2. Chemix—Draw Lab Diagrams. Simply. (n.d.). Retrieved 23 March 2022, from https://chemix.org/
3. E. coli (Escherichia coli) | E. coli | CDC. (2022, March 3). Retrieved 23 March 2022, from
https://www.cdc.gov/ecoli/index.html
4. Li, M., Liu, Q., Teng, Y., Ou, L., Xi, Y., Chen, S., & Duan, G. (2019). The resistance mechanism of Escherichia
coli induced by ampicillin in laboratory. Infection and Drug Resistance, 12, 2853–2863.
https://doi.org/10.2147/IDR.S221212
Fig 1.