Escherichia Coli Population Growth

Introduction The population of a bacterium will grow successfully in a particular pattern known as ‘logarithmic growth’ if the location is appropriate and the proper nutrients are present. The bacteria numbers will increase and most likely continue to double in this area over time with optimal conditions. Optimal conditions meaning that there are no dangers or limiting factors, to inhibit growth in this area, such as disease, predators, competition or lack of food. At first the bacteria should reproduce slowly, this is known as the lag phase but then over time it should increase more rapidly throughout what is called the log phase. This predictable pattern of growth can be called the organism’s biotic potation.
Procedure
During this exercise the population growth of the bacteria Escherichia coli (E.coli) will be measured. If the conditions are right, the E.coli population will grow more rapidly the longer it stays in that area. Turbidity, meaning cloudiness, will be how the tubes are measured to give the results of bacterial growth. The more turbid the broth the more bacteria count the tube will contain. For this particular exercise, a broth has been
prepared and separated into six test tubes labeled accordingly. The first test tube is labeled 0 as a control. This tube is a new broth that has not yet become turbid. The next tube is labeled 4hrs, meaning there has been a 4 hour growth period followed then by tubes marked at 8hrs, 12hrs, 24hrs and 48hrs, to represent the period of growth time allowed per tube. These tubes are covered, stirred and placed into a tray to wait further testing in the spectrometer. As the E.coli reproduce, the broth should become more turbid and should then show an increased level of bacteria. Each tube will be wiped clean of all blemishes and placed into the spectrometer, set to 600nm. After each tube is tested the spectrometer is then reset to 0 using the control sample. Keeping each tube wiped free of any fingerprints and debris is very important and could greatly affect the result outcome. If a tube is smudged it will appear more turbid to the spectrometer and then cause an inaccurate reading. When each tube has been carefully tested and recorded, the tubes will be compared on a scale of 0-10, 0 being the control and the least turbid and 10 being the most turbid.
Results
The tube set at 0, being the control, was consistent with just that; it was not murky at all. The tube labeled 4hrs had an absorbance value of .75nm and turbidity of 7, it was pretty murky. It was slightly higher than all others excluding the tube labeled 48hrs which had an absorbance value of 1.1nm and had a turbidity of about 9. The 8 hr tube tested at .52nm and a 5 on a scale of 10. The 12 hr and 24 hr tubes had pretty similar results with absorbance values of .6nm and .68nm, and a turbidity of 6. (Table 1)

Table 1 Growth of Bacteria in a Limited-Nutrition Medium. Time(hrs) Turbidity Intensity(0-10) Absolute Value 0 0 0 4 7 0.75 8 5 0.52 12 6 0.68 24 6 0.6 48 9 1.1

Discussion As a result of the previous steps, the study shows that the tubes did not test exactly as first expected. The control tube was quite accurate and met the expectations of this exercise. The 4hr and 8 hr tubes definitely did not have the expected results and almost seemed reversed. The turbidity and absorbance of the 4hr tube was higher than all other tubes excluding the tube marked 48hrs. The 12hr and 24hr tubes were both at lower levels of absorbance and turbidity than the 4 hr broth. The expected results were not the complete outcome in this exercise. The perfect out come would have been to have a slight increase in the level of absorbance and turbidity per tube in the order of the tubes labeled 0-48 in the order from highest to lowest. This could have happened because of several factors.
Compared to the growth of human populations (Table 2) this seems as though these results could be true. The human population did not just happen over night. Table 2 expresses that over a long period of time the human population was very low and unpredictable. From about 1400B.C. to about 1300 there were only slight increases and decreases. This would have probably been the result of diseases, more energy needs, or even food shortages. When different elements are introduced at different times these elements could aid or arrest the population growth. Over a course of 10million years the human population the human population seemed almost unpredictable. Now around the 1800’s humans began to get a grasp on the advancement of public health and advanced
industry. This was a significant turning point in the human population because as a result the human population shot up above 6billion in less than 500 years. With better health including advanced medicine, higher birth rates and lower death rates, the human population finally took a foothold and grew tremendously in population. So, in relation to this exercise, the bacteria took a few hours to become stable but maybe after 96hrs or even 198hrs the growth could have been double or even triple. Conclusion The E.coli Growth, though slow and unstable at first, did finally become more stable and look as though it could have been more successful over time. This only shows that the results of an exercise like this can have unpredictable results. With different ways of handling and testing the E.coli or even maybe the different levels of cleanliness, could affect the test outcome. To make this exercise more accurate it might be better to have the same tester handle the material through out the entire procedure.