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Concentration of disinfectant and survivability of bacteriaFeatured science projectScience project video


The purpose of this experiment is to determine the relationship between the concentration of disinfectant and its effectiveness in destroying bacteria.


The lower the concentration of disinfectant used, the higher the level of bacterial resistance.

Scientific Terms

Escherichia Coli, mutation, natural selection and incubation.


How does the disinfectant kill bacteria?

Disinfectants and antibiotics share the same purpose in general, which is to kill bacteria. Disinfectants kill bacteria by disrupting the cellular mechanisms of the bacteria. This is achieved with the disinfectant binding to certain key proteins in the bacteria which are vital for the bacteria’s survival. Some of these key proteins include the cell wall which surrounds the bacteria. With the destruction of the cell wall, the cell is split apart and eventually destroyed.

How does bacteria develop resistance?

Bacteria develop resistance through mutation. Mutation involves the random changing of the genes of the bacteria. Once a group of bacteria develops resistance, it can spread its resistant property to other surrounding bacteria through a mechanism known as plasmid exchange. From the natural selection theory proposed by the late Charles Darwin, over time, bacteria which have developed resistance will survive to produce offspring which share the same DNA. New bacteria are reproduced through binary fission give rise to a new breed of bacteria which are resistant to that disinfectant.

It is hypothesized that bacteria exposed to lower concentrations of disinfectant will develop immunity. This is because the concentration is not high enough to kill it yet sufficient for the bacteria to develop the necessary adaptations to resist the effects of the disinfectants.

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Complexity level:
Project cost ($):
Time required:
1 hour to prepare. Incubation period of 24 hours. 10 minutes for observation.
Material availability:
All of the materials mentioned should be available at the school laboratory.
Safety concerns:

Students should wear gloves and goggles at all times to prevent infection as they are dealing with microorganisms. Adult supervision is highly encouraged.