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Experimental design

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Introduction

Experimental design Summary This experiment was done in order to investigate certain factors affecting the killing of the bacterium Escherichia coli. The two factors investigated were: a) the length of time of exposure to Domestos and b) the concentration of this agent on killing E.coli. The methods used in the experiment were serial dilution and pouring Petri dishes. The results indicated that both the above mentioned factors influence the behaviour of this disinfectant agent and affect the growth of the micro-organism tested. This experiment's procedures and results are analysed and its design is assessed for accuracy and precision. Introduction Escherichia coli is considered to be a model organism for studying a variety of life's essential processes because of its rapid growth rate and simple nutritional requirements. The average human intestines contain about 1 kg of bacteria. Approximately 0.1% of these are normally E. coli. Their presence within the intestines is necessary for normal development and health - E. coli, together with other types of enterobacteria, produce vitamins which are subsequently absorbed by the body, e.g. vitamin K and B-complex vitamins. Although the normal habitat of E.coli is the intestines, they are able to survive quite well outside the body in faecally-contaminated environments like water or mud. ...read more.

Middle

When the exposure time was elapsed, cooled molten nutrient agar was used to prepare the plates where each solution was put, so four plates with different concentrations and 5 min exposure time were made. The same procedure followed but when 1 ml of Escherichia coli was added to the dilutions it was exposed for 10 minutes. Petri dishes were labeled as appropriate with the new exposure time. The same process followed again twice with different exposure times which were 15 and 20 minutes. Sixteen plates with different times of exposure and four different concentrations for each time of exposure were ready to incubate. After one week, the effect of different concentrations of Domestos on killing Escherichia coli and the length of time of exposure of this agent on killing the micro-organism could be observed. Results The laboratory experiment showed that both the disinfectant's concentration and the length of the exposure time clearly affect the killing of the bacteria. The effectiveness of Domestos was improving as the concentration or the exposure time was increasing. Figure 1 Scale 1 2 3 4 5 6 Description Impermeable Very cloudy Cloudy Little cloudy Less cloudy Permeable Table 1 Figure 1 presents the effectiveness of the disinfectant at four different concentrations (100%, 50%, 25% and 12.5%) ...read more.

Conclusion

compared to the previous two concentrations at the 5 minute mark. Assessing the experiment's procedure and results, it is observed that its design could be improved if the bacterium volume used was smaller. The results from this experiment were not very clear, because of the volume of E.coli which was added to the dilutions. Since in 0.1ml were 10000000 cells, then in 1ml, which was added in each dilution, the number of cells was extremely high. Thus it was impossible to count the cells from the plate as it was very cloudy. This lead to the utilisation of a scale to measure the effect of Dometos. Should the volume of E.coli used was lower, the colonies might have been seen and calculated and this would lead to more specific results. A successful disinfection depends on the selection of the correct chemical agent associated with an appropriate disinfecting procedure. A detailed understanding of the characteristics of each chemical agent, including the limitations and appropriate applications, is important. Also, it is essential that the chemical components used in commercial products meet established quality requirements. Reference 1) Russell, A. D., (1982)Principles and Practise of Disinfection, Preservation and Sterilization. Blackwell. 2) Tortora, G. J., Funke, B. R. & Case, C. L. (1995) Microbiology. An introduction (5th ed). Benjamin/Cummings. 3) http://www.iam.u-tokyo.ac.jp/JGAM/vol47/470202.HTM 4) http://www.centralsolutions.com/whirlpoolbathing.html 5) http://animalscience.ucdavis.edu/Avian/pfs27.htm ?? ?? ?? ?? 1 ...read more.

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