How does cost affect the
effectiveness of disinfectant
against E-Coli?
Introduction
I am going to investigate the effectiveness of different disinfectants and compare them to each other
to find the best one for its price. To do this I am going to use nutrient agar plates with E coli bacteria
on them and separate them into sections for each disinfectant and let the bacteria grow. The
disinfectants I would like to test are 10% bleach and pure bleach, Branded and non-branded home
cleaners, Branded and non-branded hand sanitizer, Rubbing alcohol, White vinegar and water .
Why?
Due to the cost of living increasing and the general public concerned about household spending I
think it would be important to investigate the effectiveness of different popular cleaning products to
see if the branded products are any better than natural or basic cleaners.
Literature Review
People tend to assume that branded and high-end goods are better than cheaper low-end products
or natural alternatives. (Casey and Littler, 2022) Discuss how social media influencers such as Mrs
Hinch promote branded cleaning products almost as a lifestyle choice individuals need to follow, and
Tik Tok creators produce cleaning product hauls and cleaning videos. In contrast, other influencers
promote a more alternative natural cleaning culture. (Goodyear, Brouillette, Tenaglia, Gore and
Marshall, 2015) state in their results that DIY cleaners such as distilled white vinegar, club soda and
tea tree oil performed best on ceramic compared to bleach but not on stainless steel. They also said
that it should be prepared freshly each day.
In one method, they use “concentrations in excess of normal recommendations” (Parnes, 1997,
p.14). This could be seen as problematic when the general public use cleaning solutions in their
homes, as it should not be recommended that people use unsafe concentrations of cleaning
products. It is vital that we do not use too much disinfectant at high concentrations as it has been
shown that “Exposure of microbes to disinfectants and non-pharmaceutical agents contributes to
the microbial ability to evolve mechanisms that increase AMR” (Lobie, Roba, Booth, Kristiansen,
Aseffa, Skarstad and Bjørås, 2021, p.324). “Antimicrobial resistance (AMR) has developed as one of
the major urgent threats to public health, causing serious issues to successful prevention and
treatment of persistent diseases.” (Dadgostar, 2019, p.3903) discusses that AMR also has significant
financial consequences due to more hospital admissions and drug usage, and Antibiotic resistance
diseases have caused a minimum of 23,000 deaths in the USA each year.
This investigation is going to use agar plates. Although (Parnes, 1997) discusses the concerns about
the type of surface could change the efficacy, they found that cleaning products such as bleach were
not affected by the surfaces and growing it on agar means that I do not have to factor in the
effectiveness of each disinfectant on different types of surfaces. (Nakachwa, Serunjogi and
Muwonge, 2021) Used Chocolate, blood, and MacConkey agar plates, but this experiment will use
nutrient agar due to not needing to isolate gram-negative bacteria. Because of this, we will
concentrate solely on testing Escherichia coli (E. coli). Chocolate or blood agar is unnecessary as E.
coli does not need nutrients from red blood cells to grow. Hence, it is easier to use nutrient agar.
(Zinn and Bockmühl, 2020, p.1) “People have been using natural products like vinegar to clean and
sanitize surfaces in the domestic environment for decades.” In this experiment, they used
, suspension tests, where the disinfectants are added directly to the bacteria in suspension. This was a
possible method for the investigation as an alternative method for using agar plates. However, the
agar plates provide a more visual representation of the efficacy compared to the suspension
method, and it removes a step making it more time efficient. In contrast to this experiment, we will
be swabbing the E. coli onto nutrient agar plates and adding the disinfectant to the plates so the
zone of inhibition can be measured to see how effective it is. This is because it is more manageable
in a school laboratory. (Zinn and Bockmühl, 2020) Showed that acetic acid reduced E. coli and
salmonella, which has been used for decades but in a simulated washing cycle, they found that
concentrations of 10 % acetic acid could eliminate E. coli. They also found that undiluted white
vinegar works well against salmonella but not E. coli.
(Zinn and Bockmühl, 2020) Showed that it is not necessary to have expensive products to clean
surfaces effectively. Using homemade and more accessible products like acetic acid (Vinegar) and
bleach led to me saying in my hypothesis that cost does not affect the effectiveness of disinfectants
against Escherichia coli, even though some are not as effective against other bacteria and viruses.
(Parnes, 1997) also promotes this by saying that undiluted ammonia and vinegar work well against E.
coli but not others like Staphylococcus aureus (S., aureus).
Project Proposal
Hypothesis
The higher the cost of the cleaner the higher the efficacy the cleaner will be.
Null Hypothesis
There is no correlation between the cost of cleaners and the effectiveness of them.
Aims and Objectives
The aim of this research is to find out if the cost of cleaners affects the effectiveness of them.
Objectives one would be to find out the best method for finding out my aim.
My second objective would be to to gather a list of suitable cleaners and carry out the experiment.
My third objective is to make sure I have a quantifiable way of measuring the efficacy.
Fourth object would be to analyse the results to if my hypothesis was correct.
Potential Limitations
Because of the method chosen there could be limitations as to generalisability or validity due to the
use of agar plates rather than real world surfaces. (Surfaces such as ceramic tile and formica as
discussed in (Parnes,1997) are these true representative surfaces in a kitchen in the 21 st century. but
due to safety concerns we are unable to do this.
Another limitation would be the accuracy of measuring the zone of inhibition (Hombach, Reinhard,
Böttger, 2013) tested the accuracy of it vs the accuracy of the sirscan automated zone reader and
discovered that the sircaner improves precision by decreasing the standard deviation
The third limitation would be insufficient sample size because I am only testing 7 different cleaners It
would mean it would have low ecological validity because it hasn’t been done in a real world
environment and the sample size is small and does not contain a large cross section of products to
get a full analysis. Because my sample size is small it might be harder to see relationships between
the cost and effectiveness in the data.
Confounding variables are also another limitation that could be factored in, potential this
experiment should be carried out in a sterile environment to stop potential contamination from
airborne bacteria, fungus and viruses. This could affect the experiment as not all cleaners kill viruses
and as my experiment is focusing purely on e-coli which is a bacteria, if any viruses get on the agar
plates they could obscure the zone of inhibition as they could have grown there.
