The E. coli bacterium can also enter the body through food and water consumed by a human. E. coli can be passed on from animal to human or human to human via direct contact with each other or by products which are contaminated with body fluids or faeces. Humans can become at risk when foods have been fertilised with contaminated faeces, when water is contaminated, when meat is undercooked and when dairy products aren’t pasteurised.
The 0157:H7 E. coli bacterium attaches itself to the mucus lining the intestinal wall, it then corrodes the intestinal wall and seeps toxins into the bloodstream and acts on the blood vessels. Once the wall is broken it can simply enter the bloodstream and release fatal toxins. The effects of E. coli can include cramps, pains, vomiting and bloody diarrhoea, if a large amount of toxins are released it can cause death or kidney failure.
pH and Bacteria
Bacteria are large domain of prokaryotic microorganisms (aem, 2012). One bacterium is typically a few micrometres in length; there is a wide range of shapes, ranging from spheres to rods and spirals. Several factors affect the growth and production of bacteria, this can include the amount of salinity, the pH level and the temperature – these are of prime importance (mic, 2012). A range of pH values can affect the growth rate of bacteria. The majority of most bacteria grow in the middle of the pH scale which is between pH 6 and pH 8, but a foodborne disease such as E. coli won’t grow in a pH condition less than 4.5. Bacteria need a physiological pH inside their cells, just like all other living organisms. Their ability to survive in extreme pH (either high or low) depends on their ability to correct for the difference between inside and out.
Aim:
The aim of this investigation is to determine the ideal pH that E. coli will most effectively reproduce and grow in.
Hypothesis:
The E. coli growing in pH7 will have the highest production of bacteria, the pH 5 and 8 will have a low reproduction and the pH 10 and Ph 3.5 will have little or no reproduction.
Safety materials
Apron
Disposable gloves
Methylated spirits
Safety glasses
Face mask
Safety Procedure
Put on apron, face mask and safety glasses.
Wash hands with soap and warm water. Follow the diagrams from the “Hand Washing Technique” chart which can be found in Appendix A.
Dry hands with hand towel.
Put on disposable gloves.
Spray bench with methylated spirits and water mix, dry with disposable hand towel.
Materials and Methodology
Below is a step-by-step procedure which will help minimise the possibility of the agar plates getting contaminated with any foreign bodies which may be present in the experimental environment.
Materials
Inoculating loops
Methylated spirits and water mix
13 petri dishes
E. coli
Method
Pre-set incubator at 37° (done once)
Put on all necessary safety materials (apron, glasses, gloves, mask)
Sterilise bench with methylated spirits; spraying then wiping.
Get Escherichia coli vial and all agar plates.
Label agar plates.
Unscrew vile with one hand, with the other dip a sterilised inoculating loop in. This should only be dipped once as this may contaminate the entire vial with contaminates.
Screw the broth together.
Pick up the agar plate opening the lid slightly.
Gently streak the agar plate with the E. coli covered inoculating loop. Once an inoculating loop has been used it must be placed into a beaker of Milton.
Turn the petri dish 90⁰C and streak the agar with the inoculating loop. Repeat this step three times. This allows the dish to be turned four times, ensuring the agar is now covered in the bacterium.
Hold the end of the parafilm on the edge of the petri dish.
Stretch the parafilm around the edge pressing down allowing it to stick. Follow along the edge with your fingers until you have passed the beginning of the parafilm.
Place dish in incubator at 37°C
Repeat steps six to thirteen until all necessary dishes are used.
Variables
The variables used in this investigation are pH 3.5, 5, 8 and 10.
Control
The control in this scientific investigation is pH 7.
Discussion
The hypothesis states ‘The E. coli growing in pH7 will have the highest production of bacteria whilst the pH 10 and pH 3.5 will have little or no reproduction’. Many of the results provided below will prove whether or not the hypothesis is correct. The condition within the experiment weren’t changed throughout, the agar plates were placed in the incubator at 37°, all bacteria grew in the same outside condition/ environment and variables weren’t changed.
pH 3.5
On the 7th of May it was observed that there was no growth – although this was the first plating and wasn’t done very well it can be said that there still wouldn’t be much growth. This is because their ability to survive in this extreme pH depends on their ability to correct for the difference between inside and out. It can be said that the E. coli disease doesn’t reproduce with a pH of 3.5. Within the next two weeks the agar plate became contaminated. It started to grow a large fungi cluster – this suggests that the plate was contaminated when made.
pH 7
On the 7th of May it was found that the bacteria was thriving, within the next 2 days the bacteria kept growing but on the 3rd and 4th day it had stopped growing and stayed minimal. This suggests that bacteria grow significantly well in this pH 7. This reproduction is known as binary fission; it is the division of one bacterium into two daughter cells. After two weeks the bacteria was still growing considerably well.
pH 10
On the first observation it was seen that there was barely any growth, but within two days the agar plate became contaminated. Throughout this investigation the fungi took over the little bacteria growth. Along with pH 3.5 it can be said that they can’t reproduce in these pH’s.
After the first plating it was decided to add a further two plates - pH 5 and 8 on the 9th of May. With the extra pH’s it will provide validity and work further towards the hypothesis to prove if it is correct or incorrect.
pH 5
Throughout the investigation it was observed the pH 5 grew similar to the pH 7. On the 10th of May it was observed that it had a high growth rate with 80 % of all streaks growing with bacteria. During the next two weeks it was found that the growth stayed at a steady rate.
pH 8
Within the investigation it was found that this particular pH had grown significantly better than the pH 7. It can be said that the bacteria prefer pH 8 rather than pH 7. During the first two days it was observed that the bacteria had grown significantly in comparison to pH 7, this therefore proves the hypothesis incorrect. This rapid reproduction occurs because the DNA molecule is attached to a point on the membrane where it is replicated.
Error Analysis
During the first practical experiment many errors were made. When swabbing the bacteria with the agar plate with the inoculating loop too much pressure was used accidentally puncturing the agar. During the next platings this was done carefully with patience, luckily this didn’t occur again. After the second plating it was decided for the third plating a Bunsen burner should be used in order to lower the risk of contamination as several of the first and second platings were. It was found that this method was very effective as the third plating wasn’t contaminated.
Improvements
To improve this scientific investigation more time was needed in order to obtain more detailed information to ensure that no contamination could occur. A monitored environment could have been used also to lessen the risk of contamination; this would help as no foreign bodies would be present.
Conclusion
This investigation outlined the different growth rates of bacteria at various pH levels. It was found that the twon with the highest pH level was Dubbo. The patients in this area drank the water that was in the pH 8; it grew the fastest out of all towns. The pH variables used are pH 3, 5, 5, 7, 8 and 10. It was found that the pH 7 and 5 had similar amount of growth and the pH 8 had a large amount; therefore the hypothesis is proved incorrect. The experimental design of this investigation has been successful in demonstrating the inhibition of five chosen pH levels. The experimental design of this investigation has gathered valid data from each experiment which can be used to prove the hypothesis is incorrect. A number of replica’s used in this investigation allowed any mistakes to be re-practiced and therefore allow higher rates of validity. The safety precautions which have been performed during this investigation have been successful; no individual contracted an E. coli disease.
Appendix A
Refereces
