The comparison of antibacterial properties of herbal products and standard antibiotics

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Karlie Whitmore

The comparison of antibacterial properties of herbal products and standard antibiotics


        This is As biology coursework, studying the area of microbiology the main investigation contains the comparison of antibacterial properties of herbal products and standard antibiotics.


        The aim is to investigate the effect of herbal products against standard antibiotics on bacteria growth. To examine the extent to which the herbal products (tea tree oil and peppermint oil) and the standard antibiotics (penicillin and streptomycin), reduce bacteria growth of E.coli and M.luteus. This will be discovered by measuring the growth of bacteria on the agar plates and comparing the results.

Background information:

        The proposed aim surrounds the study of bacteria growth and various other products, which can have an affect on the growth rate; it is therefore necessary to look deeper into the topic criteria to get a wider understanding and to help design an appropriate hypothesis.

        From self-knowledge antibiotics are chemicals produced by microorganisms, which are designed to inhibit and destroy specific pathogens when used at low temperatures. Antibiotics release chemicals, which inhibit bacterial growth and work on a specific action site. The first founded antibiotic was penicillin discovered accidentally by Alexander Fleming in 1928 from a mold culture. It can be established that herbal oils are mainly used as antiseptics to fight against bacteria growth. Peppermint is used in toothpaste, not just for the mint flavour but also due to the fact it kills off bacteria in the mouth.  

          From various websites and textbooks, it is said that all antibiotics have two names, a brand or trade name and generic name, based on the antibiotic's chemical structure or class. Although there are over 100 different antibiotics the majority come from only a few types of drugs. These types are called aminoglycoside, cephalosporin, macrolide, penicillin, quinolone, sulphonamide and tetracycline. (

There are two categories of antibiotics, which are determined primarily by their strength or rate of effectiveness, but also by their means of action against bacteria.

  • Broad spectrum antibiotics- these are used to destroy a large range of bacteria.
  • Narrow spectrum bacteria- these are specific, and are only effective against minimal numbers of bacteria.

This investigation will entail the use of penicillin and streptomycin, which are both narrow spectrum antibiotics.

Penicillin, being the first discovered antibiotic, has a mode of action that involves interference with the formation of small peptide chains cross-linking in the peptidoglycan; the main wall polymer within bacteria during cell wall synthesis. This explains the reason that penicillin is only effective against bacteria and not mammals. Mammalian cells are eukaryotic which fail to feature a cell wall, whereas bacteria cells are prokaryotic, containing a cellulose cell wall. As mentioned above, penicillin inhibits the enzymes involved with creating the cell wall, leaving the cell weak and subject to leakage of its contents, causing the cell to be destroyed.

Streptomycin works through the inhibition of protein synthesis, by binding to the bacterial ribosome’s, distorting them and preventing protein synthesis to occur. Distortion of ribosome’s results in abnormal proteins through errors in reading the code. This leads to a lack of proteins and decreases the amount of bacteria growth, killing off the cell.

Basic scientific knowledge would suggest that bacteria are single celled microorganisms, known as prokaryotic cells that fail to contain a nucleus and are very simple organisms. Due to their simplistic nature, they are also very small an inhibit places such as water, air and human bodies. The majority of bacteria are harmless, however various bacteria that inhibit the body are known as pathogens and can cause disease and infection. (Advanced biology for you)

Tea tree oil is a clear yellow in appearance with a clean, fresh medicinal aroma. It has the consistency of water and is extracted by steam distillation from the leaves and twigs of the native Australian shrub melaleuca alternifolia. The use of this oil as an antiseptic has been found to be ten times more powerful than carbolic acid and yet is non-toxic and non-irritant to the skin. (

Peppermint oil is made from the peppermint plant, which has been used for many years as a tea to calm digestion. It has an anti-spasmodic action, and calms the smooth muscles of the stomach, intestines, and uterus. Peppermint also has analgesic properties.



        There will be some sort of difference between the antibacterial capability of the herbal products and the standard antibiotics used.

Null hypothesis:

        There will be no significant difference between the antibacterial capability of the standard antibiotics and the herbal products used.  


        The standard antibiotics used will be more effective against the growth of bacteria than the herbal products used within the investigation.

Variables and controlling the variables:

        To ensure the results are accurate much attention should be paid to producing a fair test by controlling the variables. The independent variable throughout this experiment is the product being used, so either penicillin, streptomycin, tea-tree oil or peppermint oil. Meaning the dependent variable is the size of the inhibition zone on each agar plate (mm).

Regardless of the fact that the variables mentioned above will be subject to change, certain other variables will have to be controlled to ensure a fair test and valid results.


  • The equipment used- make sure the same equipment is used and that it is set up in the same way to ensure the degree of accuracy is exact.
  • Types of bacteria- two types of bacteria will be used and ensure each of the four products are tested on each bacteria. Changing bacteria would make the results void as the structures vary in different types of bacteria.
  • The amount of bacteria on each agar plate- it is not known of how many bacteria are within the broth but the amount (ml) can be controlled. If this varies it will fail to produce valid results, the more bacteria used means the more antibiotic will be needed to produce the same effect. Therefore 0.2mls of bacteria broth will be placed on each agar plate.
  • The incubator temperature- the agar plates will be incubated at the standard school temperature that, is 25° to ensure no pathogenic organisms are grown.
  • The incubation time- the longer the agar plates are incubated means the more bacteria growth. The heat from the incubation also helps to speed up the rate of growth so leaving them incubated for 48 hours is an accurate period.
  • The disc size- each disc needs to be the same size and placed in the centre of each plate. Although the concentrations of the antibiotics and herbal products range there is nothing that can be done to change this so keeping the disc sizes the same is the best possible factor.
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  • 24 agar plates- of standard size and volume. To spread the bacteria onto, and for ideal growing surface.
  • Glass spreader- choice of glass as it can withstand high heats when undergoing sterilisation. I has a smooth surface so won’t damage the agar when spreading the bacteria.
  • Sterile pipette- 1mls calibrated in 0.01 intervals for high levels of accuracy. Transfers the bacteria to the agar plate, and needs to be sterile to eliminate the chance of spreading other bacteria.
  • Bunsen burner- used for sterilisation purposes and to help reduce contamination in the air in a 10-metre radius.
  • ...

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Grammar, spelling and punctuation, all clear, correct and to a very high standard.

Hypothesis, introduction, scientific background and reasons for the experiment are all set out in a good depth of analysis and a clear and concise manner. However, the scientific reasoning behind the use of herbal products could be explored with a deeper scientific basis. The PH could also affect how the antibiotics work and this is not controlled as a factor which could affect the experiment, neither is humidity of the surroundings. The use of a pilot test shows considerations beyond the level I would expect for an A level candidate. The fact that they had to completely amend their hypothesis shows that they should have looked into the scientific background a bit clearer to make an accurate prediction from the beginning. Scientific analysis of the results and what they were is very in depth. Excellent overall response and analysis to the question.

An exemplary essay piece. The response to the question covered all available boundaries and beyond what I would expect from an A level candidate. Response to the question is very clearly and concisely set out.