Investigative project
The effect of penicillin on bacterial growth:
laboratory-based work
History of penicillin:
Antibiotics are useful medications to kill or slow down the rate of
bacterial reproduction. Before penicillin was known as an antibiotic
to treat people suffering from infections such as ‘gonorrhoea
pneumonia or rheumatic fever’ (American Chemical Society and the
Royal Society of Chemistry,1999) hospitals were full of people
diagnosed with the mentioned infections. In 1928 Dr. Alexander
Fleming has begun giving life to the discovery of penicillin as being
an antibiotic when he returned from a holiday and found out that a
white fluffy mold has formed on one of his Petri dishes where he left ONCLICK786 (2016) Penicillin,
Staphylococcus bacteria. According to the British Journal of Experimental History of penicillin, general
Pathology in June 1929, He mentioned that one of the lids of the Petri dishes structure of penicillin, medical
was opened and therefore ‘blue-green’ mold was formed on top of the uses, Susceptibility, Adverse
bacteria called ‘Penicillium notatum’. He then noticed a clear ring around the effects, Mechanism of action,
mould that has destroyed the bacteria, and to evidence this he observed from Structure. onclick786:
its studies that the mould produced a chemical that protects the mould and Penicillin, History of penicillin,
therefore kills the bacteria around it. According to the National Historic general structure of penicillin,
Chemical Landmarks program of the American Chemical Society in 2008, the medical uses, Susceptibility,
production of penicillin started when the penicillium notatum from Fleming’s Adverse effects, Mechanism of
discovery was extracted and therefore the penicillin product from the mould action, Structure - ONCLICK786
of Penicillium notatum was purified for its use as an antibiotic medicine. In the (accessed:18/11/2021)
modern days, bacteria are known to have evolved to become resistant to the
original penicillin and many other antibiotics.
ZARA RISOLDI COCHRANE (2018) ‘How does penicillin work?’ Available at:
https://www.medicalnewstoday.com/articles/216798 (accessed: 16/11/2021)
American Chemical Society National Historic Chemical Landmarks. Penicillin Production through
Deep-tank Fermentation. Available at:
http://www.acs.org/content/acs/en/education/whatischemistry/landmarks/penicillin.html
(accessed: 18/11/2021).
Bacterial growth:
Cell division is a form of bacteria being replicated during binary fission. This depends on several
factors such as temperature.
Bacteria are known to grow on nutrient broth solution which allows bacteria to multiply because the
solution provides sufficient nutrients for it to grow, as well as on agar plates where the hot molten
agar is put into sterilized Petri dishes. The bacterium is then formed into individual colonies.
Some bacteria can cause contamination therefore can affect the final investigation result of the
effect of antibiotics on bacteria. To prevent this effect sanitized Petri dishes are used but the agar gel
does not need to be contaminated with other substances than the bacteria that are tested so using a
Bunsen burner flame where an inoculating loop is heated in, the bacteria can be extracted safely
before being placed in the Petri dishes containing agar gel and after the investigation (Bacterial
, growth - Micro-organisms and their applications – WJEC - GCSE Biology (Single Science) Revision -
WJEC - BBC Bitesize, 2021).
BBC Bitesize (2021) ‘Bacterial growth - Micro-organisms and their applications’. Available at:
Bacterial growth - Micro-organisms and their applications – WJEC - GCSE Biology (Single Science)
Revision - WJEC - BBC Bitesize (accessed: 16/11/2021)
Bacteria structure and effect of penicillin on bacteria:
The structure of a bacteria cell, especially the wall consists of
peptidoglycan made of long chains of peptides and sugars, held
together by cross-links. Penicillin enters the bacteria where it stops
the formation of the cross-links. When bacterial cells are
replicating/duplicating they store enzymes that make holes in the
cell wall. The cell wall weakens as more holes are made by the
enzymes (Peptidoglycan: Definition, Function & Structure). The
environment where bacteria need to live is aqueous, this allows
water to be absorbed into the lumen of bacterium via osmosis. The high Study.com (2016) "Peptidoglycan:
pressure of water and fragile cell wall causes the bacterium cell to burst, Definition, Function & Structure."
(Alistair,2019-2021). Peptidoglycan: Definition, Function
& Structure - Video & Lesson
Alistair (2019-2021) ‘10.2.1 Penicillin’. Available at: Penicillin | CIE A- Transcript | Study.com
Level Biology 2019-21 Revision Notes (savemyexams.co.uk) (accessed:18/11/2021)
(accessed:16/11/2021)
BCA Chemistry (2014) ‘Chemistry of
Antibiotics: Cell Wall Synthesis’
https://bcachemistry.wordpress.co
m/2014/06/01/chemistry-of-
antibiotics-cell-wall-synthesis/
(accessed:20/11/2021)
Over the years Fleming informed that if penicillin is used more often than normal, this can influence
the immunity of bacteria to be stronger against penicillin (British Journal of Experimental Pathology,
1929).
There are 3 possible ways in which bacterial resistance can occur as the bacteria can produce the
enzyme penicillinase which damages penicillin. Some bacteria cells can restructure the proteins on
peptidoglycans so that penicillin is restricted to bind and therefore enter the bacterium. Other
bacteria can remove penicillin via pumps used to eliminate other substances (Penicillin: Function,
history, and resistance, 2021).
Factors affecting penicillin on bacterial growth:
- Temperature: The temperature will increase the antibiotic resistance in staphylococcus
bacteria (Study finds antibiotic resistance rise tied to hotter temps, 2021). However, the
enzymes can denature in the bacteria if a high temperature is supplied but also it cannot be
the same as the body temperature as harmful pathogens can grow, so the optimum
temperature for it is 25°C.
