The Inhibitory Effects Of A Me Essay — страница 3

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Pseudomonas putida better resists the mercury compound than Bacillus cereus. This trend is reversed in Table 4. Lastly, based on the experimental data, the average zone of inhibition was 15.0 mm for the silver nitrate solution; however for the data shown in Table 4 the average zone of inhibition for the silver nitrate solution was 19.0 mm. At this time, the reasons for these differences are not known. In relation to the resistance of bacterial organisms, the experimental data showed that Escherichia coli and Micrococcus luteus had approximately equal resistance to the effects of heavy metals. Following behind these bacteria in terms of resistance are Pseudomonas Putida and Bacillus Cereus respectively. This is shown in Tables 1 and 3. This trend contrasts that shown in Table 4

where Escherichia Coli is definitely shown to be the most resistant of the bacterial species. Table 4 also shows that following Escherichia Coli are Bacillus Cereus, Micrococcus luteus, and Pseudomonas Putida in terms of resistance. This ordering contrasts that shown by Tables 1 and 3, and the reasons for this are not clear. It is suggested that in the future more than two zone of inhibition measurements be taken for each metal-bacteria solution to obtain more data points. Based on the experimental data, the fact that Escherichia coli would be resistant to the heavy metals was predicted by the hypothesis. The hypothesis did not, however, predict the resistance of Micrococcus luteus. The resistance of the Escherichia coli to heavy-metal effects could possibly be related to the

fact that Escherichia coli is a gram-negative bacterium. As a result, the heavy-metal ions may have a hard time permeating the outer lipopolysaccharide layer present in gram-negative bacteria. The consequence is increased resistance to heavy metals. The reason for the resistance of the gram-positive Micrococcus luteus is unknown. It might, however, be related to the fact that this type of bacteria may have heavy-metal-resistant plasmids. The data in Table 1 show one interesting trend: The copper sulfate solution had quite a pronounced effect on the Escherichia coli as compared to the other bacteria. Based on the ability of Escherichia coli to resist the effects of heavy metals and based on the inability of the copper sulfate solution to affect any other bacterial organisms, it is

felt that a mistake was made in the experimental procedure (Footnote 2). In particular, it is thought that instead of a Escherichia coli and copper sulfate solution, this solution was probably Escherichia coli and a silver nitrate solution. The reason for this is that the average diameter of the zone of inhibition of the Escherichia coli and silver nitrate solution is very similar to the average diameter of the zone of inhibition of the Escherichia coli and copper sulfate solution. Table 1 also shows that there weren’t any zones of inhibition around the paper disks of the control. This indicates that the paper disks did not affect the growth of the different bacteria. Based on the experimental data, the original hypothesis that Escherichia coli would be the most resistant

bacteria was verified. The ability of Micrococcus luteus to have approximately the same resistance as Escherichia Coli was not, however, predicted by the hypothesis. In relation to the effects of the heavy metals on the bacteria, the original hypothesis correctly predicted that Hg would have the largest effect. Furthermore, the hypothesis also predicted the ability of Ag to have an effect on the bacteria. The hypothesis did not, however, correctly, predict the very slight effect of the Cu solution on the bacterial cultures. Literature Cited Biology 108. 2001. Biology 108 laboratory manual 2000-2001 University of Alberta, Edmonton, Alberta, Canada. Brock, T. D. and M. T. Madigan. 1991. Biology of microorganisms. Prentice Hall, Englewood Cliffs, New Jersey. Campbell, N. A., L. G.

Mitchell, and J. B. Reece. 1999. Biology. Benjamin/Cummings, Menlo Park, CA. Cenci G., and G. Caldini. 1985. Injury by Heavy Metals in Escherichia coli. Bulletin of Environmental Contamination and Toxicology 34:188-195. De Vincente, A., M. Aviles, J.C. Codina, and P. Romero. 1990. Resistance to antibiotics and heavy metals of Pseudomonas aeruginosa isolated from natural waters. Journal of Applied Bacteriology 68: 625-632. Mossman, M. “Months after E. coli outbreak, Walkerton residents still weary of water supply.” http://www.nandotimes.com/noframes/story/0,2107,500291929-500463058-503086695-0,00.html (Feb. 11, 2001).