Bacteria and Disinfectants
Purpose: To see how concentration can affect the performance rate of disinfectants in killing microorganisms.
Aim: I want to investigate how different concentrations of disinfectant inhibit the growth of bacteria.
Hypothesis: I predict that the stronger the concentration of Savlon, the more bacteria is inhibited from growing. I think this because Savlon is an antiseptic disinfectant which is a bactericide, therefore, the stronger the concentration of savlon, the more bacteria is killed and stopped from growing.
Variables:
The independent variable in this investigation, is the concentration of Savlon - we will be using.
The concentration of the Savlon will be done through a diluting it with water (9 drops of water, 1 drop of solution).
The concentrations of this solution will be 100%, 10%, 1% and 0.1%.
To keep this investigation constant, there needs to some controlled variables. Firstly, the agar plates we will be using are nutrient agar plates rather than other ones as they are used to support the growth of a wide range of non-fastidious organisms. They are eligible of growing bacteria and fungi, because of the great amount of nutrients needed for bacteria growth.
Another controlled variable is the use of filter paper. This is used to soak up the same amount of solution rather having different types of paper. Also, another variable is keeping the same size of filter paper discs to ensure that the results are more accurate.
To keep this investigation constant, there needs to some controlled variables. Firstly, the agar plates we will be using are nutrient agar plates rather than other ones as they are used to support the growth of a wide range of non-fastidious organisms. They are eligible of growing bacteria and fungi, because of the great amount of nutrients needed for bacteria growth.
Another controlled variable is the use of filter paper. This is used to soak up the same amount of solution rather having different types of paper. Also, another variable is keeping the same size of filter paper discs to ensure that the results are more accurate.
In this investigation, the dependent variable which we will be measuring is the clear zone surrounding the discs of Savlon. The 'clear zone' is the name of the area where the bacteria on the agar plates does not grow, or kills the bacteria cells.
The measuring process of this will be carried out through using a ruler to measure the diameter of the circle - hopefully - which will be surrounding the discs. The measurements will be done in millimeters.
Equipment:
- Agar Plate
- Savlon - antispetic
- Vivid
- Yoghurt - the bacteria growing
- Beaker
- Filter Paper
- Hole Punch
- Tweezers
- Dropper
- Dimple Tray
- Ethanol
- Bunsen Burner
- Tape
Method:
- Firstly, begin with collecting all of the equipment needed.
- With a clear agar plate, make sure to keep the lid on it as much as possible and divide bottom of the plate into four sections using a vivid. Label each section according to concentration (1=0%, 2=10%, 3=1%, 4=0.1%).
- Dilute some yoghurt with water until you are left if a watery consistency. Pour 10mL into agar plate to form a thin layer on top of the gel - may need to be swirled around to cover every part of the gel.
- Drain out any excess yoghurt in the plate - do not touch the gel.
- Take a sheet of filter paper and using the hole punch, punch out four small discs of the same size.
- Taking the dimple tray, a clean dropper, a beaker of Savlon and a beaker of water, begin with forming different concentrations of Savlon - 10%, 1% & 0.1%.
- Using a clean dropper, put 10 drops of Savlon into a well in the dimple tray - remember to clean out the dropper after every time you use it to collect Savlon. This can be done through collecting water from a beaker and squirting it out, doing this three times.
- Put 9 drops of water in the second well, and one drop of savlon. Make sure to stir the solution and proceeding to rinse out the dropper once again. This is the concentration of 10% Savlon.
- Drop 9 drops of water once again into another well, and take one drop of the 10% and mixing it into the new dimple of water, forming a new solution. This is the concentration of 1% Savlon.
- Take 9 more drops of water into another dimple, add one drop of the 1% percent solution and mix to form the 0.1% Savlon concentration.
- Finally, add water to another dimple. This is the 0%, or ‘control’.
- Turn on your Bunsen Burner, making sure you have your filter paper, dimple tray, agar plate, some tweezers and ethanol - making sure to put the lid back on the container when not using it.
- Take the tweezers and dip the end of them into the ethanol, then run it through the Bunsen flame to sterilize.
- Soak one disc per solution and place the discs into the center of it’s designated section on the agar plate.
- Finally, using tape, seal the lid to the plate so the agar plate doesn't open.
Repeat these steps on two more agar plates to ensure you get more accurate results.
Results:
Final Result
Data Table
Analysis
This set of data shows three tests of this investigation and in almost every case, the highest concentrations have a greater diameter, and the lowest concentrations have the smallest diameters. However, within this investigation, there appeared to be one outlier, and this can be seen in agar plate 2's results, where the 1% concentration has a greater diameter compared to the 10% concentration, unlike the other two plates.
In the line graph, he blue line represents the size of the clear zone - area where no bacteria had grown - compared to the concentration of Savlon.
The red line in the line graph is a trend line. This line shows which direction the results seem to be going, and in this situation, the trend line seems to be showing that it is increasing. This means, that the higher the concentration of savlon, the greater the diameter of the clear zone.
Conclusion:
In this investigation, my hypothesis was correct. The stronger the concentration of Savlon - antiseptic - the more bacteria is inhibited from growing. My hypothesis was proved correct because when looking over the data I collected, a trend can be seen. In the graph, results show an increasing trend - as seen in the red trend line. This means that by increasing the concentration, the size of the clear zone is also increased. Or, in other words, the stronger the concentration, the more bacteria growth is inhibited, therefore forming a greater clear zone.
Discussion:
Bacteria are small, single cell microorganisms and they exist in groups of millions. There are three main bacterial shapes - sphere shaped, rod shaped and spiral. Bacteria cells can live within soil, water, plants, animals, and so on. The life process of bacteria is movement, respiration, sensitivity, growth, reproduction, excretion and nutrition - or MRS GREN for short. In this investigation, we were looking more into the growth and reproduction side of bacteria. The growth and reproduction of bacteria is an asexual process, dividing one cell into two daughter cells. This process is known as Binary Fission.
Binary Fission occurs asexually, when a grown parent cell, divides into two halves producing two new daughter cells which will eventually do the same thing at some point as a way of reproducing.
The diagram above shows the growth of bacteria, growing to the right size to split into two. These two new cells are identical clones of the mother cell they originated from, due to there being no other genetic code - another parent - involved in this reproduction.
This a graph showing the growth of bacteria when there is nutrients present. During the lag phase, there is little bacteria, beginning to take in nutrients and synthesizing their DNA and proteins. From there, the exponential phase is where the bacteria begin to replicate themselves - cloning - and the amount of bacter grows. During the stationary phase, the essential nutrients needed start to run low, and the growth rate of bacteria is equal to the death rate of bacteria. As the nutrients completely run out, it means that the bacteria can no longer reproduce and the bacteria slowly decreases. This is known as the death phase - the death of bacteria.
What is Savlon?
Savlon is an antiseptic which brand. It contains two antiseptics called Cetrimide and Chlorhexidine Gluconate.
Cetrimide is an antiseptic, having a mixture of quaternary ammonium salts - including cetrimonium bromide. Chlorhexidine is an antiseptic and disinfectant used on skin before surgery is performed on a patient and also used to sterilize surgical instruments.
What is a disinfectant and an antiseptic?
A disinfectant is a chemical which kills bacteria, and prevents it from growing. Antiseptics do the same thing, except they are used on the skin as it does not do as much harm. An antiseptic is a solution which prevents the growth of microorganisms which can cause diseases. Antiseptics can also be known as bactericides, and these are known to inhibit the growth of bacteria, and the stronger the bactericidal is, the more bacteria is killed off. This provides us with a reason for why the higher concentrations of Savlon resulted in greater clear zones - area where bacteria has not been able to grow.
Disinfectants can work in multiple ways. Depending what disinfectant it is, it oxidises the molecules on the surface of of the bacteria cells. This disrupts the cells wall and cell membrane and the proteins on the surface begin to become damaged and forming clumps. This happens quickly and the bacteria does not work fast enough to fight against this process. Then, the cells can't handle it and splits apart, killing the bacteria.
growth What Is Bacteria? What Are Bacteria?
Nutrient Agar: Composition, Preparation and Uses Evaluation:
With this experiment, we carried it out three times to gain a more accurate result. It was a good idea considering that one of our three agar plates did not give us the result we were looking for. This one poor result gave us an outlier to work around. The outlier can be found in agar plate 2, with the 1% percent concentration. This result was over 10mm greater in diameter compared to the other two plates. Therefore, this meant leaving it out when calculating the average diameter for the final results.
For next time, I feel that we could improve on this experiment by having a bit more time to actually accurately soak the filter paper and place onto the plate correctly - rather than rushing within 5 minutes at the end of the class. Also, allowing the plate to dry once the filter paper is placed so that it doesn't move around - there was a lot of movement when it came to our paper.
Discussion:
Bacteria
Bacteria cells have a specific structure. The outermost wall is called the capsule and it simply protects the bacteria. Inside, is the cell wall - which helps to keep the structure of the cell - and the cell membrane - which controls what enters and exits the cell.
Within the cell, the long twisted thing in the middle, is DNA, and it holds the genetic code or instructions. As seen in the photograph, there are two small plasmid and they are DNA which codes for processes which are not essential. The small, circular things are ribosomes, and they are where proteins are made. Everything within these cells are held together with cytoplasm which is a gel like texture.
On the outside of the cell structure, there are short spikes which stick out and they are called Pili. Their purpose is to transfer genetic material. Also, the cell has a tail, and it is called the flagellum. The flagellum is there to help the cell to move.
Binary Fission occurs asexually, when a grown parent cell, divides into two halves producing two new daughter cells which will eventually do the same thing at some point as a way of reproducing.
The diagram above shows the growth of bacteria, growing to the right size to split into two. These two new cells are identical clones of the mother cell they originated from, due to there being no other genetic code - another parent - involved in this reproduction.
This a graph showing the growth of bacteria when there is nutrients present. During the lag phase, there is little bacteria, beginning to take in nutrients and synthesizing their DNA and proteins. From there, the exponential phase is where the bacteria begin to replicate themselves - cloning - and the amount of bacter grows. During the stationary phase, the essential nutrients needed start to run low, and the growth rate of bacteria is equal to the death rate of bacteria. As the nutrients completely run out, it means that the bacteria can no longer reproduce and the bacteria slowly decreases. This is known as the death phase - the death of bacteria.
What is Savlon?
Savlon is an antiseptic which brand. It contains two antiseptics called Cetrimide and Chlorhexidine Gluconate.
Cetrimide is an antiseptic, having a mixture of quaternary ammonium salts - including cetrimonium bromide. Chlorhexidine is an antiseptic and disinfectant used on skin before surgery is performed on a patient and also used to sterilize surgical instruments.
What is a disinfectant and an antiseptic?
A disinfectant is a chemical which kills bacteria, and prevents it from growing. Antiseptics do the same thing, except they are used on the skin as it does not do as much harm. An antiseptic is a solution which prevents the growth of microorganisms which can cause diseases. Antiseptics can also be known as bactericides, and these are known to inhibit the growth of bacteria, and the stronger the bactericidal is, the more bacteria is killed off. This provides us with a reason for why the higher concentrations of Savlon resulted in greater clear zones - area where bacteria has not been able to grow.
Disinfectants can work in multiple ways. Depending what disinfectant it is, it oxidises the molecules on the surface of of the bacteria cells. This disrupts the cells wall and cell membrane and the proteins on the surface begin to become damaged and forming clumps. This happens quickly and the bacteria does not work fast enough to fight against this process. Then, the cells can't handle it and splits apart, killing the bacteria.
growth What Is Bacteria? What Are Bacteria?
Nutrient Agar: Composition, Preparation and Uses Evaluation:
With this experiment, we carried it out three times to gain a more accurate result. It was a good idea considering that one of our three agar plates did not give us the result we were looking for. This one poor result gave us an outlier to work around. The outlier can be found in agar plate 2, with the 1% percent concentration. This result was over 10mm greater in diameter compared to the other two plates. Therefore, this meant leaving it out when calculating the average diameter for the final results.
For next time, I feel that we could improve on this experiment by having a bit more time to actually accurately soak the filter paper and place onto the plate correctly - rather than rushing within 5 minutes at the end of the class. Also, allowing the plate to dry once the filter paper is placed so that it doesn't move around - there was a lot of movement when it came to our paper.
