Hypothesis: What type of disinfectant is best at preventing bacterial/microbial growth?

If Isopropyl Alcohol, Bleach and Quaternary Ammonium based disinfectants are applied to different sections of the same, commonly touched, wooden handrail for the same amount of contact time and are then swabbed to observe bacterial growth, then it will be observed that the different disinfectants will have a varied amount of effectiveness against bacterial growth when compared to a control test. One of these disinfectants observed will yield a lower number of bacterial colonies once grown. This will be observed since each disinfectant possesses different chemical properties and mechanisms of killing bacteria which may cause variation in effectiveness. 

Research: What type of disinfectant is best at preventing bacterial/microbial growth?

Bacteria & Microbial Life (General Information to Build Background in Bacteria):

To begin, I will define microbiology. Microbiology is the study of microscopic organisms too small to be seen by the naked eye. All microbial organisms fall into 4 categories: bacteria, viruses, fungi and protozoa. These four categories can be further split. Viruses are differentiated by genome and are either double stranded or single stranded. Fungi are differentiated by their cellular composistion, and can be yeast or mold. Yeast are single cellular whilst mold are multicellular. 

All bacteria are prokaryotes, meaning they are single celled and lack organelles like mitochondrea, golgi bodies, E.R's and others. Bacteria can also either be gram-positive or gram-negative, determined by the composition of its outer layers. Gram positive bacteria have a plasma membrane, followed by a thick layer of peptidoglycan, a chemical which helps maintain cell shape and prevents ruptures in cell membrane. Gram negative bacteria too have a plasma memberane followed by a peptidoglycan layer, but the peptidoglycan layer is far thinner and is followed by another outer membrane. Bacteria have many shapes including cocci (spherical), bacilli (Rod-Shaped) and spirilla (Spiral shaped). Some cocci bacteria include, diplococci (2 sphered), tetrads (4 sphered), streptococci (Coccus in a long chain) and staphylococci (Coccus in a large group). Some Bacilli bacteria include coccobacillus, bacillus(rod), diplobacillus (2 rodded), strepto bacilli (Rods in a long chain). Finally, some spirilla include, spirilla, vibrios and spirochete. Bacteria can be benificial to us, for example in the microbiota of our digestive system. Bacteria in our gut help us with many tasks, such as digestion with the production of enzymes which help break down food into sugars. 

Properties/Types of Disinfectants:

In this experiment I will be testing the effectiveness of three disinfectents: Isopropyl Alcohol, Bleach and Quaternary Ammonium Compounds (Quats).

Isopropyl Alcohol:

• Properties/Info: Isopropyl alcohol C₃H₈O is a colorless liquid which has a strong odor, it evaporates quickly and is commonly used in hand sanitizer. Rubbing alcohol is often a solution of C₃H₈O and water.
• How it Kills Bacteria: Isopropyl Alcohol primarily kills bacteria by distrupting cell membranes by destroying (denaturing) protiens in the cell. Alcohol denatures the proteins within the bacteria/organism by breaking the bonds which hold the protiens together. Once the proteins are destroyed, the cell ceases to function properly and the bacteria dies.

Bleach:

• Properties/Info: Bleach, containing Sodium Hypochlorite (NaOCl), is composed of a positively charged sodium atom and a negatively charged hypochlorate atom. It is green or yellow in tint, is soluable in water and is corrosive. Sodium Hypochlorate is unstable but Sodium Hypochlorate Pentahydrate is stable. Household bleach has only 3%-8% NaOCl.
• How it Kills Bacteria: The Hypochlorite found in bleach attacks the protiens of the bacteria, causing them to lose structure and function, forming large and useless clumps called aggregate. Bleach is a strong oxidizer, releasing chlorine ions to the cells; this damages cells proteins, nucleic acids and other parts. and  These proteins are like "machines" which perform vital tasks for the bacteria such as nutrient uptake, cellular respiration and other vital tasks. Bleach kills these "machines" which stops these important processes from happening, killing the bacteria.

Quaternary Ammonium:

• Properties/Info: Quats are "ammonium salts", and are composed of a positively charged nitrogen atom in the center bonded with other atoms such as carbon and chlorine. Quats have no odor, don't stain surfaces and don't corrode metals. They can kill many types of micobial life including bacteria, fungi and viruses, [Quats.org]
• How it Kills Bacteria: Quats are positively charged, which allows it to attatch to the negatively charged cell membranes of the bacteria. Once attatched, the quats rupture the membranes of the bacteria, causing the internal contents of the bacteria to leak; killing it.

Bacterial Growth (Stages of Growth, Factors Influencing Bacterial Growth, Growth on Surfaces):

STAGES OF GROWTH - Bacteria grow and multiply exponentially each generation via a process known as binary fission where a cell replicates it's DNA and components before splitting into two new cells. Bacterial cells only begin dividing once they recieve sufficient nutrients and meet the conditions required for growth. There are 4 phases to cell growth:

• Lag Phase: The first phase in bacterial culture and growth is the lag phase where the bacteria adjust to their new environment, begin preparing enzymes to start growing rapidly; cells prepare for growth.
• Log Phase: The second phase in bacterial culture is the Log phase where there is an exponetial growth in bacterial population as the cells begin to divide; there is rapid cell division, doubling cell count each generation.
• Stationary Phase: The third phase is called the stationary phase where the population number of cells slows down and stops as nutrients begin to deplenish; Cell death is equal to cell reproduction.
• Death Phase: The final phase in bacterial culture is the death phase where the nutrients are depleted and the population declines; Cell death exceeds cell reproduction.

FACTORS AFFECTING GROWTH - There are many factors that must be regulated for optimal bacterial growth including pH, temperature, water and oxygen levels:

• Temperature: Bacteria have different temperatures best for their growth. Psychrophiles thrive in cold temperatures below 15 degrees Celsius, Mesophiles thrive in moderate temperatures between 20-45 degrees Celsius, Thermophiles thrive in temperatures of greater than 70 degrees Celsius.
• pH: Bacteria have different pH's best for their growth. Acidophiles thrive in Acidic environments with a pH of 1-5, Neutrophiles thrive in neutral environments with a pH of 5-8, Alkalophiles thrive in basic environments with a pH of >9
• Oxygen: Bacteria have different Oxygen requirements for growth. Obligate Aerobes are bacteria which require oxygen, Faculative Anaerobes are able to grow with or without oxygen but do better with oxygen, Aerotolorant Anaerobes grow equally as well with or without oxygen and finally Oblicate Anaerobes die in the presence of oxygen.
• Water: All bacteria grow better in areas with water and moisture

Incubators and Agar Plates in Bacterial Growth:

Since there are many factors which affect the growth of bacteria (Listed above), an incubator must be used to regulate these factors to ensure the microbes grow properly. Inconsistent, uncontrolled environments aren't conducive to bacterial growth; The control of environment is necessary to maintain accuracy and precisity in an experiment.

• Common Household Bacteria are Mesophilic, Neutrophilic, and Faculative Anaerobes. I will be trying to replicate these favourable conditions in my incubator to aid bacterial growth. 

Since Bacteria require sufficient nutrients to begin rapidly growing, a nutrient rich medium must be used to support bacterial growth. Agar, a gel-like substance made of seaweed, will be used as this nutrient rich medium and will be poured into petri dishes to culture the bacteria. This agar plate ultimately allows the bacteria to grow and be observed to view colony count.

Lab Safety Practices:

#1. Be monitored by an Adult when doing the experiment

#2. Wear PPE's (Personal Protective Equipment) to avoid getting sick or getting exposed to the chemicals used:

• Gloves
• Goggles
• Masks
• Coat

#3. When using chemicals, transport, use and dispose of them safely

#4. Properly label everything used

#5. Carefully disinfect and dispose of cultured bacteria

 

Variables: What type of disinfectant is best at preventing bacterial/microbial growth?

1. Controlled Variables 
- Surface Swabbed: Wooden Handrail
- Contact Times for Disinfectants on Surface (15 seconds)
- Swabbing Technique: Each section of the handrail will be swabbed two times to minimize experimental error
- Nutrient Rich Agar Petri Dishes
- Environmental Conditions: Time spent in incubation, Temperature, Pressure, Oxygen & others 
- Other Materials: Sterile Cotton Swabs, Tape for Labelling, etc.

2. Manipulated Variables
- Type of Disinfectant applied to the surface prior to swabbing (Quats, Isopropyl Alcohol, Bleach)

3. Responding Variables
- Quantity of Bacterial Colony Growth observed on Agar Plates

4. Control & Variable Groups
-Control: Sections of the handrail with no disinfectant applied, just water
-Variable: Different sections of the handrail with the different disinfectants applied (Quats, Isopropyl Alcohol, Bleach)

5. Potential Errors/ Variables External to the Experiment
- Variation in the Environmental Conditions of the bacteria in growth
- This will be addressed by keeping bacteria insulated in a box and placed within a closet to maintain consistent conditions.
- It will be attempted to increase the accuracy of this experiment by swabbing each section of the surface (wooden handrail) 4 times to counteract experimental error
 

Experimental Procedure: What type of disinfectant is best at preventing bacterial/microbial growth?

Materials:

1.  Commonly Touched Surface (Wooden Handrail)
2. 8 Petri Dishes with Nutrient Rich Agar
3.  Sterile Cotton Swabs for Bacterial Collection
4. Box with lid, Blanket and Lamp or other Source of Consistent Heat (Controlled Environment)
5.  Isopropyl Alcohol Based Disinfectant (Rubbing Alchohol)
6.  Quaternary Ammonium Based Disinfectant (Quats)
7.  Filtered Water
8.  Bleach Based Disinfectant
9.  Tape and Marker For Labelling
10.  Timer for measuring contact time of disinfectants on the surface (15-30 seconds before swabbing)
11.  Personal Protective Equipment (Goggles, gloves, mask)
12. Small Borders to Divide Each Section of the Handrail
13. Phone or Camera to Document Bacterial Growth

Procedure:

#1. Preparation

• Prepare petri dishes with nutrient rich agar
• Label Petri Dishes as "Control, Alco. (Isopropyl Alcohol), Bleach and Quats (Quaternary Ammonium)," with tape and marker
• Divide and Label 4 sections of the surface (Wooden Handrail) with the same corresponding names as the petri dishes with tape and marker
• Create a data table or some other form of information collection to be used throughout the experiment
• Wear Gloves, Goggles and other protective equipment to avoid contaminating bacteria and agar or getting sick when handling microbes

#2. Applying the Disinfectants

• Evenly apply a small amount of each disinfectant to one of the four corresponding sections using a sterile cotton swab to spread the disinfectant
• Evenly apply a small amount of filtered water to the control section
• Use a timer to keep the contact time of the disinfectants fairly consistent throughout, in order to give each disinfectant equal time to take effect (Wait 15 - 30 seconds of contact time before swabbing)

#3. Swabbing Surfaces

• After applying all disinfectants, rub a different sterile cotton swab on each of the 4 sections, while rotating the swab in order to collect as much microbial life. After, apply those swabs to their corresponding agar plates
• Use a zig-zag motion while rotating the swab when applying the collected microbial life to the agar plates. This is in order to transfer the maximum amount of bacteria over a greater area of the plate
• Apply a reasonable amount of pressure when collecting and transferring microbial life to the plates

#3. Growing the Bacteria 

• Place each labelled petri dish and place them in an enclosed box, wrapped in a blanket, with a lamp pointed at them, inside a dark closet to maintain a consistent and controlled environment for bacterial growth
• Take a photo of the agar plates once, at the same time, every day to observe growth phases. Check briefly (10 mins max) as to subject microbial life to less drastic change in environment
• Finish culturing bacteria in 3-4 days and remove bacteria from make-shift incubator for final observations

#4. Observations

• Count, on average, how many bacterial colonies there were for each group
• Or, generally, observe how much variation in bacterial mass there was between groups, if any, if counting is not possible.
• Take a photo for future reference

#5. Analysis/ Conclusion

• Compare the quantity of bacterial colonies between different disinfectant groups, using the control as a bottom line, to see which disinfectant was best at reducing bacterial growth
• Make a scientific conclusion using data and evidence from the observation and analysis phase

#6. CYSF Work

• Put my findings on the CYSF platform and create a presentation and trifold about the experiment

 

Observations: What type of disinfectant is best at preventing bacterial/microbial growth?

Aim of Observations:

In the following observations it will be observed the number and general size of bacterial colonies formed on 8 petri dishes divided into 4 disinfectant sections: Control, Alcohol, Quats & Bleach. The aim is to describe which disinfectant contributed to the growth of the least overall bacterial mass. Comparing these observations on number of colonies formed and general size of colonies, the disinfectant which minimized the formation of bacterial colonies and colony sizes (which contributed to least overall microbial mass) will be found.

 

Description Of Bacterial Growths:

Data Table of Bacterial Colony Quantities

Control Section:

Control #1

• Bacterial Colony Size & Quantity: 
  • 4 moderate colonies, 12 punctiform colonies
• Bacterial Colony Color: 
  • 11 white colonies, 1 yellow colony
• Bacterial Colony Shape: 
  • All colonies were round in shape
• Bacterial Colony Opacity: 
  • All colonies were opaque
• Bacterial Growth Uniformity:
  • The colonies grew mostly on one side of the plate.
  • The bacterial growth wasn't uniform

Control #2

• Bacterial Colony Size & Quantity: 
  • 2 Large Bacterial Colonies, 2 moderate bacterial colonies, 5 small bacterial colonies and ~13 punctiform bacterial colonies
• Bacterial Colony Color: 
  • 5 yellow colonies, 17 white colonies
• Bacterial Colony Shape: 
  • 2 filamentous colonies and the rest are round
• Bacterial Colony Opacity: 
  • Filamentous colonies are translucent, the rest are opaque
• Bacterial Growth Uniformity:
  • Larger bacterial colonies grew on one half of the plate while, smaller and punctiform colonies generally grew further away. 
  • The bacterial growth wasn't uniform

Comparison of Replicates:

• Control 1 had far fewer and smaller bacterial colonies than control 2
• Control 1 had less diversity in colony color and appearance, having only 1 yellow colored colony and lacking filamentous colonies all together
• Control 1 has some of the same types of colonies as Control 2
• Control 1 had less bacterial mass and bacterial variation than control 2, this could potentially be due to error in swabbing technique.

 

Isopropyl Alcohol Section:

Alcohol #1

• Bacterial Colony Size & Quantity: 
  • 5 Small Colonies, >150 punctiform colonies
• Bacterial Colony Color: 
  • 9 yellow colonies, rest of colonies were white
• Bacterial Colony Shape: 
  • ​​​​​​​All colonies were round
• Bacterial Colony Opacity: 
  • All colonies were opaque
• Bacterial Growth Uniformity:
  • The majority of bacteria were punctiform and grew consistently throughout the petri dish
  • Bacterial growths were mostly uniform

Alcohol #2

• Bacterial Colony Size & Quantity: 
  • 5 small colonies, >100 punctiform colonies
• Bacterial Colony Color: 
  • 5 yellow colonies, the rest are white
• Bacterial Colony Shape: 
  • All are round in shape
• Bacterial Colony Opacity: 
  • All opaque
• Bacterial Growth Uniformity:
  • ​​​​The majority of bacteria were punctiform and grew consistently throughout the petri dish
  • Bacterial growths were mostly uniform

 

Comparison of Replicates:

• Alcohol 1 and Alcohol 2 have around the same quantity of bacterial colonies and those colonies have around the same sizes
• They share similar diversity within their colonies
• Alcohol 1 has the higher amount of punctiform colonies than Alcohol 2 by a slight margin

Comparison to Control:

• Unlike the ununiform bacterial morphology of the control tests, the alcohol tests yeilded consistent growths:

  • Most growths were white, round, opaque and punctiform  

• The control test had far more diversity:

  • In the control test there were, large filamentous colonies, white small/punctiform colonies and moderate yellow colonies

• Generally, the alcohol test yeilded a higher quantity of colonies but a lower colony size.

 

Quaternary Ammonium Compound Section:

Quats #1

• Bacterial Colony Size & Quantity: 
  • 3 small colonies, ~25 punctiform
• Bacterial Colony Color: 
  • 3 yellow colonies, rest are white
• Bacterial Colony Shape: 
  • All are round in Shape
• Bacterial Colony Opacity: 
  • 3 bacteria colonies are transparent, the rest are opaque
• Bacterial Growth Uniformity:
  • Bacteria grew throughout the petri dish 

Quats #2

• Bacterial Colony Size & Quantity: 
  • No bacteria
• Bacterial Colony Color: 
  • No bacteria
• Bacterial Colony Shape:
  • No bacteria 
• Bacterial Colony Opacity:
  • No bacteria 
• Bacterial Growth Uniformity:
  • No bacteria

Comparison of Replicates:

• Quat 2 had no bacterial growth unlike quat 1
• This could be due to poor swabbing technique or poor agar, as the rest of the variable stayed consistent.  
• I will refer only to quat 1 moving forward

Comparison to Control:

• The total microbial mass was far reduced when compared to the control tests
• The types of bacteria stay generally similar when compared to the control tests

Bleach Section:

Bleach #1

• Bacterial Colony Size & Quantity: 
  • ​​​​​​​2 punctiform colonies
• Bacterial Colony Color: 
  • ​​​​​​​All colonies were white
• Bacterial Colony Shape: 
  • ​​​​​​​All colonies were round
• Bacterial Colony Opacity: 
  • ​​​​​​​All colonies were opaque
• Bacterial Growth Uniformity:
  • ​​​​​​​There were two colonies located on one part of the petri dish

 

Bleach#2

• Bacterial Colony Size & Quantity: 
  • ​​​​​​​3 punctiform colonies
• Bacterial Colony Color:
  •  All colonies were white
• Bacterial Colony Shape: 
  • ​​​​​​​Colonies were round
• Bacterial Colony Opacity: 
  • ​​​​​​​Colonies were opaque
• Bacterial Growth Uniformity:
  • ​​​​​​​Colonies were uniform

 

Comparison of Replicates:

• Bleach 1 and Bleach 2 have around the same quantity of bacterial colonies and those colonies have around the same sizes
• They both had almost no bacterial formation

Comparison to Control:

• Compared to the control, the bleach prevented the majority of bacterial growth.

 

 

 

Photographs Of Bacterial Growths:

 

 

 

Analysis: What type of disinfectant is best at preventing bacterial/microbial growth?

Introduction:

In this experiment, the effectiveness of four different disinfectants (Isopropyl Alcohol, Quaternary Ammonium Compounds, and Bleach) in preventing bacterial growth on agar plates was observed. The comparison of bacterial growth between the control group and the different disinfectant applied groups reveals the ability of each disinfectant at killing bacteria. This effectiveness will be analyzed in this section by comparing the different observations made in the previous section.

The differences that were observed in bacterial growth between the control and disinfectant groups suggests that the disinfectants tested have variation in levels of effectiveness in reducing bacterial colony formation. What was observed were the differences in bacterial colony diversity, colony size and quantity. The disinfectant which was most effective will be interpreted from which caused the formation of colonies with least diversity, size and quantity.

Difference in Size/Quantity

The following will describe the disinfectants which contributed to the least-most bacterial growth. Bleach had led to the formation of 2-3 punctiform bacteria. The second least microbial growth was the Quat/QAC which caused the formation of ~25 punctiform bacteria and three small bacteria. Third were the alcohol tests which caused the formation of over 100-150 very small punctiform bacteria and 5 small bacteria. Last is the control test where 0-2 large, 2-4 moderate, 0-5 small and 12-13 punctiform bacteria formed across tests. Overall, bleach contributed to the formation of the most colonial mass. 

Differences in Diversity

The following will describe the disinfectants which contributed to the least microbial diversity within colonies (Color, Shape, Opacity, Uniformity). The group with the least colony diversity was bleach with all white, round, and opaque colonies. The group with the second least colony diversity was the Alcohol section, containing over 100 punctiform colonies, all white, round and opaque. The alcohol section however did also have 5 yellow, round and opaque colonies. The group. The group with the third least bacterial diversity is the Quat section where there were both yellow and white colonies, 3 transparent colonies and 25 opaque colonies, but all of them were round. Finally, the control tests had the most diversity, boasting 5 yellow and 17 white colonies, 2 filamentous colonies and 21 round colonies, and both translucent and opaque colonies. Ultimately, bleach contributed to the prevention of the most colony diversity.

How Could the Different Mechanisms of each Disinfectant Contribute to the Variation?

The different mechanisms of how each disinfectant kills bacteria most likely contributed to the observed variation in bacterial growth. Bleach is a strong oxidizer and disrupts cellular components like proteins, nucleic acids and other very important parts of all cells, this method is able to kill a wide array of microorganisms. This is seen in the tests where the overall microbial masses and diversity of colonies were almost  none. Quats disrupt bacterial cell membranes by rupturing them, causing the internal components of the cell to “leak” out, killing the cell. Some bacteria may resist Quats however, as seen in the tests where the number of colonies were significantly, but not all, reduced. Isopropyl Alcohol primarily kills bacteria by disrupting cell membranes by destroying (denaturing) proteins in the cell. Perhaps there is a correlation between this mechanism of Isopropyl Alcohol and formation of high quantities but low sizes of bacterial colonies. Variations in these mechanisms may be the reason why there is variation in the effectiveness of the different disinfectants.

Conclusion of Analysis Part.

In conclusion, these findings support the hypothesis that disinfectants can vary in effectiveness against the prevention of bacterial growth on surfaces. This is possible due to the varying mechanisms each disinfectant uses to eliminate bacterial growth. The disinfectant which proved most effective at preventing baterial growth was ultimately the Bleach test. This was followed by Quats, Alcohol and the Control Test. There was noticable differences in the level of bacterial growth reduction between all groups, supporting the initial hypothesis and answering the experimental question.
 

 

 

Conclusion: What type of disinfectant is best at preventing bacterial/microbial growth?

The purpose of this experiment was to find which disinfectant best reduced the formation of bacterial colonies. In this project three disinfectants, Isopropyl Alcohol, Bleach & Quaternary Ammonium, were applied to a commonly touched surface, a wooden handrail in a home. After the application of these disinfectants, each section was swabbed, and the collected samples were cultured in a makeshift, at home, incubator to observe the quantity of visible microbial colonies. The effectiveness of each disinfectant was found by comparing the size and number of bacterial colonies created with the use of each disinfectant to the quantity of colonies created in a control test without disinfectants. The aim of this experiment is to analyze the disinfectant best at reducing the quantity of microbial colonies on an agar dish.

It was expected that if Isopropyl Alcohol, Bleach and Quaternary Ammonium based disinfectants were applied to the same surface, for the same amount of time and were swabbed and incubated to observe bacterial growth, then it would be observed that the different disinfectants would have a varied level of effectiveness against bacterial growth when compared to a control test. It was expected that one of these disinfectants observed will yield a lower number of bacterial colonies once grown. 

This was expected because each disinfectant has different mechanisms of killing bacteria which may cause variation in how well they counteract the growth of said bacteria. Isopropyl Alcohol primarily kills bacteria by disrupting cell membranes by destroying (denaturing) proteins in the cell. Bleach is a strong oxidizer, releasing chlorine ions to the cells; this damages cells proteins, nucleic acids and other parts. Finally, quats, being positively charged, attach to the cell walls of bacteria and rip it apart, killing it. The reason variation in the effectiveness of each disinfectant was expected was due to these differences in mechanisms.

From this experiment, what was observed was that there were varying levels of bacterial growth from each disinfectant used. Here is some quantitative data observed: The control tests had high levels of diversity within the bacterial growths with 2 Large Bacterial Colonies, 2 moderate bacterial colonies, 5 small bacterial colonies and ~13 punctiform bacteria colonies. The Isopropyl Alcohol did the poorest job at preventing bacterial growth, allowing for the formation of 5 small colonies and over 100 punctiform bacteria colonies within both tests. The Quat’s did the second best job, allowing for the formation of 3 small colonies and ~25 punctiform colonies. Finally, bleach contributed to the formation of only 2-3 punctiform bacteria colonies between both tests. These results were quantitative and provide insight into the quality of colonies.

When observing the agar plates, some qualitative observations were made. The control test yielded the highest amount of diversity between the colonies. There were colonies of sizes between large and punctiform. There were also varying shapes of colonies, such as some being round and smooth, others being irregular and filamentous. The alcohol test had the least diversity. In the alcohol test, there were over a hundred punctiform bacteria, all round, smooth and white. The alcohol test didn’t reduce the quantity of formed bacteria but rather the size. The QUAT’s test produced bacteria similar to the control test but just at a lower quantity. Finally the bleach test prevented almost all colonies from forming. These results were qualitative and provide insight into the properties and appearance of the colonies.

These observations indicate some trends. First off, the data indicates that there is a noticeable difference in the effectiveness of the disinfectants. Bleach seems to be most effective, reducing the quantity/size of bacteria and overall bacterial diversity. This is followed by Quat/QAC’s and then Isopropyl Alcohol. Also, while Bleach and Quats lower both the quantity and size of colonies, the Isopropyl Alcohol led to the formation of hundreds of tiny colonies. The alcohol reduced the sizes of colonies but led to the formation of a high quantity of colonies (>100 punctiform colonies). There is also a correlation between the size/quantity of colonies and the diversity of colonies. As the general quantity and size of the colonies decreases, so does the diversity. These trends are significant because they answer the experimental question, “What type of disinfectant is best at preventing bacterial/microbial growth,”  by displaying results which allow for the deduction that bleach is most effective. 

The hypothesis of this experiment was correct. It was hypothesized that Isopropyl Alcohol, Quats/QAC and Bleach would have varying levels of effectiveness against the growth of bacterial colonies and that one would be more effective than the others. Bleach out performed the other disinfectants and there were high levels of variation between tests in regards to the colony size, quantity and diversity. 

In conclusion, the goal of this experiment is to find the effectiveness of different disinfectants when preventing bacterial growth on agar plates. Through the observation and analysis of bacterial colonies, it was found that bleach displayed the greatest results in reducing both the quantity and diversity of bacterial colonies. Next were the Quats/QAC, isopropyl alcohol, and the control tests. The observed trends show that the mechanisms of how each disinfectant kills bacteria may cause the variation in the effectiveness it has against bacterial growth. The findings support my hypothesis that disinfectants vary in their ability to prevent bacterial growth on surfaces. 
 

Application: What type of disinfectant is best at preventing bacterial/microbial growth?

Home Cleaning and Hygiene Practices:

This experiment is important as it relates to concepts of public health, home disinfection and basic hygine practices. The finding from this experiment can inform people about the most effective disinfectant at preventing the growth of microbial life. As many household surfaces are frequently touched, they contain many microorganisms, some harmful, meaning disinfection of surfaces like handrails, countertops, handles and others is crucial to the hygine and health of all of us. Knowing that Bleach and Quats/QAC are best for disinfection, people can effectivley disinfect surfaces and prevent microbial contamination. 

Maintaining Sterility in Hospitals and Laboratory Settings:

Some areas must maintain total sterility, eliminating all microbial contaminants is a must. In hospitals, vulnerable individuals seek help, bacterial contamination could harm these vulnerable individuals far more significantly than others. In laboratory settings, such as in the fields of biology, sterility must be achieved in order for error to be mitigated. Such as in this experiment, outside contaminants couldn't be allowed as it would inhibit precise results from being garnered. The findings that bleach is most effective at disinfection is significant as it can lower the risk of contamination in fields of health/medicine and experimental fields of biology. The knowledge that bleach leads to the formation of little to no bacterial colonies is significant information for fields where the formation of all all bacteria must be prevented for safety or accurate testing.

General Public Knowledge/Health

Knowledge on the effectiveness of multiple types of disinfectant is important. The findings of this experiment could be used to better educate the public on proper hygine practices regarding disinfection of commonly used surfaces using the right disinfectants. In general, the spread of public infections and disease could be reduced if people became more knowlegeable of the bacteria which grow on common surfaces and how practises such as santization and disinfection can stop the spread of disease in public spaces. Recently, there was a global pandemic called Covid - 19. This disease was wide spread and it wasn't airborne, it was spread through touch. If people had known of proper disinfection methods, perhaps general public health would have been greater. 

Sources Of Error: What type of disinfectant is best at preventing bacterial/microbial growth?

Inconsistent Techniques:

• Variation In Swabbing Technique:
  • The replicate "Quat #2" in the quats test yeilded no bacterial growth. This could be due to poor swabbing technique not allowing for the proper transfer of microbial life from the surface to the agar dish
  • The first control plate had noticably less bacterial growth than Control #2. This could also be due to variation in swabbing technique​​​​​​​
• Variation In Agar Dishes:
  • ​​​​​​​ I had bought pre-poured agar dishes which arrived through shipping. The agar dishes were sterile and wrapped in multiple layers of plastic. However, if any of the agar gel had issues, such as not being able to provide adequate resources, it could've caused for error in bacterial growth.
• Uneven Application of Disinfectants Across Surface:
  • When applying disinfectant on the surface, there could be places where more disinfectant was applied than others. This variation could've lead to the discrepancies observed between Quat #1 and Quat #2  

Small Range of Disinfectants

In this experiment, I only used 3 types of disinfectants, Bleach, Isopropyl Alcohol and Quats due to them being most commonly availible in households. I however, neglected other types of disinfectants with other mechanisms of action such as Hydrogen Peroxide, Chlorine based disinfectants, Phenolics, Iodine disinfectants and others. Having more disinfectants would have more accuratley answered the question and would provide a more broad and comprehensive experiment. Having more disinfectants would provide greater applications of my results and make the experiment as a whole more accurate.

Observation Method

The method I used to observe quantity of bacterial growth involved just counting colonies and observing their sizes. This method suffices for the scope of this experiment and allowed me to draw conclusions about the effectiveness of each disinfectant. However, I assume there are more sophisticated data analysis methods when observing bacterial cultures on agar plates which would allow for more precise and quantifiable numbers of bacterial growths on these petri dishes. These statistical tests and analytical techniques fall out of my grasp of microbiology and aren't necessary for forming conclusions, they just allow for more accurate findings. 

 

 

Experimental Procedure: What type of disinfectant is best at preventing bacterial/microbial growth?

Background Research Citations (APA):

Quats Education Program. (2020). What are quats? Quats.Org. https://quats.org/what-are-quats

Oncology Times. (Dec 25, 2008). New Research Shows Why Bleach Kills Bacteria. Oncology Times. https://journals.lww.com/oncology-times/fulltext/2008/12250/new_research_shows_why_bleach_kills_bacteria.9.aspx#:~:text=%E2%80%9CWe%20found%20both%20in%20vitro,specifically%20activated%20to%20increase%20resistance.%E2%80%9D

(Mar 08 2024). Sodium Hypochlorite. Vedantu. https://www.vedantu.com/chemistry/sodium-hypochlorite

Karla Moeller. (Date not on site). How to Break Protiens. Arizona State University, Ask a Biologist. https://askabiologist.asu.edu/activities/breaking-proteins

Nuwan Gunawrdhana. (Feb 13, 2023) "Does alcohol kill viruses? What to know." Medical News Today. https://www.medicalnewstoday.com/articles/does-alcohol-kill-viruses

ATP. (2018). Introduction To Microbiology. ATP YouTube. https://www.youtube.com/watch?v=fU0XO1X1tAE&t=7s

Armando Hasudungan. (2013). Microbiology - Bacteria Growth, Reproduction, Classification. Armando Hasudungan YouTube. https://www.youtube.com/watch?v=7Lh-M-rX86Q

DIY bama. (2019). How to Grow Bacteria. DIY bama YouTube. https://youtu.be/JIZ7lj3y4MQ?si=5P4M8GcOCtIpVIfi

Microbiology Mantra. (2023). Bacterial Growth Curve & Generation time Calculation. Microbiology Mantra YouTube. https://youtu.be/8AhDxAQaDOA?si=TsvpAGnX0nJlGNNC

Osmosis from Elsevier. (2021). Bacterial Structure and Functions. Osmosis from Elsevier YouTube. https://youtu.be/b15Hy3jCPDs?si=dZZTXYn8Q2IdMwMC

Acknowlegments: What type of disinfectant is best at preventing bacterial/microbial growth?

I acknowledge these following individuals for their help and contributions to this scientific inquiry:

1. My Science Teacher - Nairn Mclean, for providing feedback on parts of my project and helped my refine my initial experimental design.
2. My Parents - For aiding me in allocating the necessary materials required for the completion of this experiment.
3. My Scientific Supervisor - Gavin Tackney, for providing me a platform on the CYSF