These are the results for 10-5 yeast dilution
The number of colonies in 10-5 yeast dilution = 14
1cm3 of the original suspension: 14*50*105= 7*108 cfu cm ¯³
These are the results for the 10-6 dilution
The number of colonies in 10-6 yeast dilution = 11
1cm3 of the original suspension: 11*50*106= 5.5*108
I have used the 10-5 and 10-6 dilutions as these were the only dilutions that shown single colonies. The others were to numerous to count or there was no growth.
Total count
Total number of cells = 131+128+168=427
Total count: 427*3*10,000= 12,810,000 cells cm¯³ = 1.281*107 cells cm¯³
Discussion
The results of the viable count show the most growth on the 10-1 dilution which then decreases as the dilutions get less concentrated. The 10-1 to 10-4 were too numerous to count. Dilution 10-7 had no growth. There wasn’t a substantial number of cells and therefore, they were not visible. The dilution 10-8 had one colony - this is anomalous result due to the fact that the petri dish may have been moved suddenly or when added on the petri dish there may have been a drop or a little spray when squeezing the pipette. If this had been realised, the experiments could have been repeated in order to attain more accurate results. To stop this occurring, more precision and care must be taken if further experiments were to be done. For Dilutions 10-5 and 10-6, The colonies were counted as the concentrations weren’t too low or too high. The result 10-5 is
5.5* 108 cfu cm ¯³ and 10-6 is 7*108 cfu cm ¯³.
The result for the total count is 1.281*107 cells cm¯³. There are problems with this method, however. The number of cells in each grid maybe more concentrated or less concentrated as they are not evenly spread over the all the grids. So therefore this makes the results inaccurate as the concentration of cells vary. Also, the cells clump together-this makes it very difficult to count the number of cells. Moreover, there will be human error involved as the cells have to be counted through a microscope. So therefore more or less cells may have been counted. One problem with this technique is you are unable to distinguish between dead and living cell, so the number of living cells cannot be equated.
There are advantages and disadvantages with viable and total count technique. Firstly, with the viable technique the advantage of this technique is that it only counts the living cells.
The disadvantages of the of viable count are the confluence of cells, this prevents the ability to distinguish colonies. So there could be more or less colonies therefore making the results inaccurate as you are unable to distinguish them. To solve this a drop of each dilution could placed on a agar plate then spread this will then distribute the cells so there is less chance convergence clumping . Other disadvantages are that the incubation and medium may not support all the growth of all the cells so there could be fewer colonies. This could be avoided by choosing a optimum incubation and medium to ensure the best results. This would then make the experiment more accurate. If the apparatus are not sterile then there could be other micro organisms which contaminate the culture-this may restrict the growth of the cells. The only way to solve this is to ensure the apparatus are sterile, ensuring that aseptic technique is used to prevent this from occurring. Assumption.
An advantage of the total count is that it allows you to see individual cells. But there is a problem with this which is that you are unable to establish weather the cells are living or dead.
The disadvantages are that the test is very time consuming as each individual cell needs to be counted. Also the distribution of cells will be uneven-this will mean there will be larger or smaller numbers on different grids. The only way to try prevent this is to ensure that the solution is mixed well before added into a chamber.
There are two main problems with both techniques- those being the precision error of apparatus and human error. These will have effected the experiment as it may have created higher or lower concentrations which may have affected the number of colonies grown or the number of cells counted. To ensure this did not effect the experiment too much, great care was taken when carrying out the experiment.
To make this experiment more accurate more results are required. To improve the viable count experiment it would have been more accurate to pipette a drop of diluted suspension onto its own medium then use the Spread Plate Method. This would then prevent the colonies from clumping as the cells are spread out. Another idea would be to produce a larger range of dilutions so there fore you will get a greater range of viable results. A way to improve total count would be to have fresh cultures when creating dilutions.
Both methods enabled me to gain the results that I required. This was not the most accurate way as both methods have error. The techniques would have to be improved. This may mean producing a wider range of dilutions. Another idea would be to pipette a drop of diluted suspension onto its own medium then use the Spread Plate Method this prevents clumping. Producing a greater number of results, would then mean I could produce more accurate mean.
References
a) Biology seventh edition. Cambell and Reece
b) www.uwcsea.edu.sg/bio
MC-2
1. This could be due to a number of factors. Using non-sterile equipment could cause contamination. This may affect the growth on the plates. As it may inhibit growth or enhance the growth. Another factor would be the length of time that the culture is left to incubate for. If the plate is left for longer then the cells would grow producing larger colonise. the only limiting factor would be nutrients, so if left to long cells may begin to die. The conditions that the cultures are kept in will affect the growth. If they were left in hot conditions then the rate of reaction would be increased. This there for means increased . Keeping the cultures in cool conditions will restrict the growth of the bacteria.
2. Viable count/total count * 100= percentage of viable count.
3.
Yoghurt production Pharmaceutical industry
Food testing Shelf life dates.
Water testing
Bioremediation
Dentists - plaque
References
