Discussion Section

Hey guys, the discussion is 2 and 1/3 pages long 1.5 spaced and 3 pages when double spaced. I'm still working on the future research part but it shouldn't take long. Also Lisa's is the first part and mine begins with "While our hypothesis tested to be correct..."


Our hypothesis of the efficacy of three mouthwashes on both oral and E. coli bacteria was supported by our results. As shown in Table 1 (don't know if it'll actually be table 1), Listerine Antiseptic mouthwash was the most effective at killing both the oral flora colonies and the E. coli colonies. Listerine showed only 4 colonies on the oral bacteria plate and 2 colonies on the E. coli plate, both results much lower than Scope, Tom's and water. The next most effective mouthwash was Scope. Scope showed 45 colonies on the oral plate. Tom's appeared to have only a minor influence on the growth of either bacteria and had results similar to those of water for both bacterial colonies.
As stated in the introduction, Listerine contains thymol, a chemical with strong antiseptic properties, as its active ingredient. It also contains ethanol, sodium benzoate, and benzoic acid, all of which have antibacterial properties. Listerine's superior efficacy is most likely a result of its high percentage of ethanol (26.9%). Like Listerine, Scope contains both sodium benzoate and benzoic acid as well as the additional antibacterial cetylpyridinium chloride. It does not contain thymol (the active ingredient in Listerine) and its ethanol content is much lower—only 15%. Because of this, it is less effective at killing bacteria. Despite being less effective at killing bacteria, Scope may in fact be more effective than Listerine at eliminating bad breath. The inclusion of cetylpyridinium chloride (CPC) in Scope specifically targets the sulfur compounds in one's mouth that produce especially malodorous breath[1].
Tom's contains no proven antiseptics or antibacterials. Its active ingredients, witch hazel and ascorbic acid, both have astringent properties which could make it harder for bacteria to survive. This explains why the E. coli colony for Tom's is slightly smaller than that of water—3.3cm in Tom's to 4.65cm in water. Tom's is also alcohol-free, which is good in terms of oral comfort, but ineffective in the sense that bacteria aren't actually being eliminated.
The alcohol in both Scope and Listerine may also be promoting halitosis. Alcohol is a desiccant—it dries out the mouth, eliminating the natural antibacterials that humans produce in their saliva. Without this natural aid in eliminating bad breath, the compounds that are not eliminated by the antibacterials in the mouthwash are left to grow unmasked by the mouth's saliva, leading to bad breath[2]. (this is not an incredibly reliable source, but i thought the point they make is interesting)
While our hypothesis tested to be correct, our lab was not without experimental errors. As outlined in the methods and materials section, we used sterile technique as well as sterile equipment such as cotton swabs and inoculating loops throughout the experiment; however, the use of the word “sterile” is only nominal. For example [put example here]. Another error in experiment to identify is the fact that the liquids were not spread evenly along each plate or equally in comparison to other plates. This existing inconsistency may have resulted in more or less coverage of bacteria killed in some plates. We also plated the liquids one after another and did not keep track of the amount of time that each soaked for. Having this initial imbalance of different soaking times could have caused some plates to have had more exposure to their respective liquids, therefore producing better results. Not only did the soaking times differ, but the incubating times as well. As stated earlier in the paper, before we began plating, two tubes were incubated longer than the third. Another part to note is that because we broke the E.coli: Scope plate, we had to re-plate the E.coli: Scope and incubate it independently from the other plates. The incubation times differed again at this point in the experiment and created more discrepancies.
Once results were produced, we collected the data by counting the colonies on the bacteria plates. We did this by marking the plates above the colonies with whiteboard markers. We split the task amongst the group instead of having a consistent counter. This may be classified as another error because one group member could have had a different idea as to how big each colony was, thus allowing room for deviation. Also, the counting of the colonies was not done in the most accurate fashion; another experimental error to add to the list. In addition to all the errors above, our group did not have enough time to do more trials. We were not able to produce realistic results (for example at one point our water had a zone of inhibition) until our last test, which we only had enough time to create one generation for. Therefore our conclusions are heavily dependent on our one successful experiment.
Having had the experience of executing a number of unsuccessful tests and trials, our group would do a few things differently if we were to run the experiment again. Recurrent errors that were identified relate to the lack of consistency such as the uneven plating of the liquids, the inaccuracy of soaking and incubation times, and the potential various methods used to count the colonies. It is imperative that every aspect of the experiment is done in the same vein. We would need to create a system to make sure that each plate received even amounts of their respective liquids and were spread evenly, record exact times for soaking and incubation to have homogenous numbers and resulting data, and lastly form a technique allowing for uniformity in the counting of colonies (or perhaps have one person perform the task).
[1] http://patft.uspto.gov/netacgi/nph-Parser?Sect1=PTO2&Sect2=HITOFF&p=1&u=%2Fnetahtml%2FPTO%2Fsearch-adv.htm&r=1&f=G&l=50&d=PTXT&S1=%226723305%22&OS=
[2] http://www.therabreath.com.au/mouthwash.html