Abstract
The experiment is aimed at observing the effects of temperature on growth of microorganism, in this case Escherichia coli and Bacillus stearothermophilus. This happens through use of culturing of the bacteria on different parts of the lab with different temperatures. The goal of the experiment is to get the most suitable temperature that will allow for growth and the temperatures where there would be little or no growth of the microorganisms. In this case it is easier to device a method of controlling the pathogens through temperature variations.
Introduction
Microorganisms are minute organisms that are visible only with the help of a microscope. They include bacteria and other organisms like viruses and many others. In our case we will be studying the growth of bacteria. The growth of bacteria is affected by various factors which include: temperature, moisture, food and even competition from other microorganisms. If two or more bacteria share the same environment then they are likely to compete for the available resources and this will affect their growth. On the hand they could also compete amongst each other for the food and water available. In our experiment the factor to be studied is temperature and its effects on the growth of bacteria; what effect does variation of temperature have on the growth of bacteria.
Escherichia coli are a gram positive bacterium found in the human digestive system (Ryan, K. & Ray, G., 2004, p 22). They are rod shaped and mostly found in the colon of mammals. They are considered to be harmless to the host but could at times cause food poisoning which may result into diarrhea. They are microscopic organisms and cannot be viewed by naked eyes. As for Bacillus stearothermophilus, these are gram positive bacteria that exist in temperatures varying at around 30- 70°C. They are mostly found in the soil. In case they infiltrate food staffs, the cause rotting thus being harmful to other living organisms for instance humans. They too are rod shaped and microscopic in nature.
Materials and methods
In order to carry out the experiment one would require: a Petri dish used for the growth of bacteria, a source of heat for sterilization, inoculating wire used to transfer up the bacteria for growth and the samples strains that one should experiment on. Since we are dealing with microorganisms one would require a microscope to view the samples. A stain is also necessary so as to clearly view the samples under the microscope and in our case crystal purple will be the appropriate stain as it is used for staining gram positive bacteria which we are dealing with. Slides and cover slips are also required so as to mount the samples.
During inoculation one first heats the inoculating wire until it is red hot, then let it cool this is because it may denature the bacteria when used when red hot. After cooling gently pick a small sample from the colony and place in agar plate for incubation. During incubation all other factors are kept optimal, i.e. pH, moisture and food for growth of bacteria. The samples are put to grow in different temperatures, that is 25, 37 and 45°C and given equal amount of time to grow.
After growth using the same inoculation technique one picks a small sample of the grown bacteria from different sections of the experiment make mounts based on the sections from which the experiment was conducted. Using crystal purple stain, stain the sample and cover them with cover slips ready for observations under the microscopes. From this one can tell the amount of growth by comparing the samples in terms abundance of different strains of bacteria in different slides.
Results/Observation
Discussion
Living organism can be classified from multi cellular organism like animals to single celled organisms like bacteria. Bacteria are classified under prokaryotes. They are generally minute in size having a diameter of a few micrometers. Bacteria can be classified into main groups: gram positive and gram negative bacteria. Ryan KJ, Ray CG (2004) says that, “Escherichia coli generally known as E.coli is found in other mammals.” E.coli has both positive and negative effects in human digestive system. As for positive effects it can be used in the production of vitamin K, which is essential in the human functionality.
On the hand E.coli can be classified causing serious health disorders in humans. As for Bacillus stearothermophilus, they are also gram positive bacteria that are closely related to the genus Bacillus. The growth and abundance of their population is largely affected by various factors. They include moisture, temperature, the level of acidity or alkalinity E.coli, and also time among others.
According to the above results the growth of E.coli at 45°C in almost all the sections of the lab is low compared to the other section of 37 and 25 which are the optimal temperatures for the growth of E.coli. The percentage of E.coli is high this because of their large numbers thus competing hard for the available resources for growth that includes food and water. At 45°C the growth of E.coli is hindered this is due to high temperatures which are not favorable for their growth. Thus the other strains experience more growth thus increasing their numbers and depriving E. coli of the available growth resources.
The two strains exist in different environments thus have different growing conditions. For instance, E. coli is found in the human bodies that has an optimum of about 37degrees centigrade. While Bacillus stearothermophilus was removed from a pool with temperature was approximately 45 degrees. According to this we can see that generally Bacillus stearothermophilus grow in a slightly temperature as compared to E. coli. The increase or decrease in temperature would definitely alter the growth mechanisms thus affecting bacteria growth and eventually affecting their abundance in an environment. In regard to the temperature microorganisms can be classified into three psychrophilic, thermophiles and mesophilies.
Psychrophilies this are microorganisms that grow on low temperatures. They can comfortably grow and live in temperature ranging from -10 to 20°C. Above which their chemical processes which enable them to grow are affected thus affecting their growth and reproduction processes. Madigan M, Martinko J (editors). (2005) claim that these organisms are mostly found in cold area regions. Most psychrophilies contaminated food staffs for instance milk, causing milk spoilage. They enter the milk through animal feed. Psychrophiles reproduce by means of cell division (Stiles M., Holzapfel W.,1997).
The mitosis process can only occur under the above temperatures. If psychrophiles are exposed to temperatures that are below -10°C, they become inactive and in that case will no be able to grow causing a decrease in their abundance. On the other hand high temperatures cause death of many cells. This happens as a result of cell being denatured due to the high temperatures which the organisms are exposed to.
Mesophilies are bacteria with the capability of growing at temperature ranging between 10 to 50°C (Cooper G.M., 2000). It is under this category that Escherichia coli fall into. Most microorganisms fall under this category. They are found in environments for instance human body where they can carry out their biochemical process effectively. Escherichia coli grow and reproduce at an optimum temperature of 37°C which is equivalent to 98.6°F. Mikelsaar, M., Zilmer M. (2009, p 56) expound that they are facultative anaerobes they have the capability of growing in areas with or without oxygen.
Under these temperatures condition they are able to grow and reproduce effectively thus increasing their abundance. E. coli reproduce by means of asexual reproduction. Some E. coli have the ability to grow and reproduce at temperatures above 37°C but below 49°C, above which the cell will be denatured causing their death.
Some microorganisms have the ability to live and reproduce in hot environment with temperatures ranging above 50°C. These are known as thermophiles. Brevibacillus agri are thermophiles, they are able to grow in environments with high temperatures. They can withstand temperatures up to 70°C without being denatured. If thermophiles are exposed to temperatures below 20°C they become inactive. It hinders their growth and development thus hindering their growth and abundance. Despite thermophiles are capable to survive in very high temperatures, they too can be denatured at temperature above 70°C. They are also denatured at extremely high temperatures thus killing the cells.
Shortcomings
There are some challenges that one endures during the experiments. For instance, during transfer of bacteria one can easily contaminate the samples thus interfering with the results. Another challenge is that during the transfer of bacteria one could denature the cells due to the high temperatures of the inoculating wire during sterilization and hence interfering with the final result. Similarly, bacteria grown in room temperature will experience different temperatures this might interfere with the growth of bacteria, hence producing results that are not desired. Bacteria growth is affected by various factors for instance moisture oxygen and other factors and in the experiment variation of temperature is the factor to be studied hence if other factors are not constant then desired results will not be achieved.
Conclusion
Generally, bacteria growth is affected by various factors. In order to get desired results one need to keep all factors constant. Different temperatures affect different strains of bacteria. Very high temperatures kill the cells thus most people use heat as a preservation method. Food staffs that can be contaminated by bacteria are normally heated at very high temperatures and pressure in order to kill the bacteria that cause food spoilage. For foods that can not be heated they are frozen to temperature below 0°C this inactivates the bacteria thus preserving the food. Therefore, temperature variations are being used by many food processing industries as preservatives of their food products.
References
Cooper, G.M. (2000). The cell: a molecular approach. Washington, D.C; ASM Press.
Madigan, M. & Martinko, J. (2005). Brock Biology of Microorganisms (11th ed.). New Jersey; Prentice Hall.
Mikelsaar, M. & Zilmer, M. (2009). Lactobacillus fermentum ME-3 – an antimicrobial and antioxidative probiotic. London; Oxford Univrsity press.
Ryan, K.J. & Ray, C.G. (2004). Sherris Medical Microbiology (4th ed.). McGraw Hill.
Stiles, M. & Holzapfel, W. (1997). Lactic acid bacteria of foods and their current taxonomy. London; Macmillan.