Effects of Alcoholic Dilutions on Bacterial Growth

1. Effects of Alcoholic Dilutions on Bacterial Growth Project by: Lauren Pease Grade 9

2. Problem • What effect do different dilutions of alcohol have on bacterial growth? • Does alcohol have a greater inhibitory effect on the growth of gram-negative or gram-positive bacteria?

3. Research of Bacterial Species • Staphylococcus epidermidis is found on the outer layer of the human skin and is the leading pathogen of foreign body infections. -it is typically immune to most antibiotics • Escherichia coli lives in the intestinal tract of the human body and many other animals.

4. Research of Gram-negative vs. Gram-positive Bacteria • Gram-positive bacteria -cell wall contains a thick layer of peptidoglycan that encompasses the entire cell wall • Gram-negative bacteria -cell wall contains a thin layer of peptidoglycan located only between the cytoplasmic and outer membrane • Peptidoglycan is a polymer that consists of glycan and peptide chains which is responsible for inflexibility of cell walls in prokaryotes

5. Research of Ethanol Alcohol • Often referred to as “pure alcohol” • Ethyl alcohol without additives or denaturants • Is a group of chemical compounds whose molecules contain a hydroxyl group bonded to a carbon atom • Made by the fermentation of sugars

6. Hypothesis • If there is a higher percentage of alcohol content, the alcohol will greater inhibit the growth of the bacteria. • Also, if there is an equal percentage of alcohol used on the Staphylococcus Epidermidis and Escherichia Coli, then the Staphylococcus Epidermidis will be greater affected by the alcohol.

7. Materials • 5 Petri dishes of Staphylococcus epidermidis(gram-positive bacteria) • 5 Petri dishes of Escherichia coli (gram-negative bacteria) • 4 different dilutions of ethanol alcohol at 10 mL each with dilutions of 25%, 50%, 75%, and 100% • 40 sterile disks submerged in the dilutions of ethanol alcohol (4 on each dish) • Sharpie • Tape • Goggles and gloves were used for safety

8. Variables • Independent Variables -dilutions of ethanol alcohol • Dependent Variables -the effects of the alcoholic dilutions of the bacteria • Constants -the temperature of the incubator -time each Petri dish spent in the incubator • Controlled Variables -Petri dish of Staphylococcus epidermidisand Escherichia coli that contained two blank disks and two water submerged disks

9. Procedure • The dilutions of ethanol alcohol were created by using the alcohol and a specified amount of water. • Aseptic technique was used to swab the two types of bacteria onto five Petri dishes each. • The sterile disks were immersed into different dilutions (one disk for each percentage of alcohol) and then four were placed on each Petri dish. • For the controlled variable, two disks submerged in water, and two blank disks were placed in each Petri dish. • The Petri dishes were then placed in the incubator and left there for two days. • Observations on the dishes were made both days. • Then measurements were taken of which bacteria’s growth was greater inhibited and which alcohol dilution caused it.

10. Data

11. Data (continued)

12. Data (continued)

13. Data (continued)

14. Conclusion • The hypothesis was not supported by the data. • I hypothesized that the dilution of 100% ethanol alcohol would greater inhibit the growth of the Staphylococcus epidermidis more than it would inhibit the growth of Escherichia coli. I also hypothesized that there would be a significant difference between the 25% and 100% dilutions of alcohol with the 100% being most effective. • The dilutions of alcohol had no significant difference in inhibiting the bacteria’s growth regardless of the percent of alcohol content. • The alcohol had a greater inhibitory effect on the Escherichia coli than the Staphylococcus epidermidis. • This is most likely the result of the overuse of alcoholic sterilizers in hand sanitizers and hospitals because bacteria are becoming immune to the alcohol’s ability to be lethal.

15. Conclusion (continued) • Improvements could be made to the experiment by testing more than one type of gram-negative and gram-positive bacterium. • Also, one of the new forms of bacteria that could be tested should be found somewhere besides the human body. • Further experimentation could be done by testing ethanol alcohol on other forms of bacteria that may be found in hospitals to greater verify this immunity of Staphylococcus epidermidis to ethanol alcohol

16. Works Cited Bukhari, Mohammad. "Staphylococcus Epidermidis." University of Connecticut- Department of Molecular and Cell Biology. N.p., 27 Sept. 2004. Web. 10 Feb.      2011. <http://web.uconn.edu/mcbstaff/graf/Student%20presentations/      S%20epidermidis/sepidermidis.html >. "The cell wall surrounds and holds in the microbe." The Microbial World. University of Wisconsin-Madison, 2006. Web. 31 Jan. 2011. <http://www.microbiologytext.com/ index.php?module=Book&func=displayarticle&art_id=60>. "Comparative Characteristics of Gram-Positive and Gram-Negative Bacteria." University of Maryland . N.p., n.d. Web. 10 Feb. 2011.      <http://www.life.umd.edu/classroom/bsci424/BSCI223WebSiteFiles/      GramPosvsGramNeg.htm>.

17. Works Cited (continued) "Peptidoglycan." Dorland's Medical Dictionary for Health Consumers. The Free Dictionary, 2007. Web. 31 Jan. 2011. <http://medical-dictionary.thefreedictionary.com/peptidoglycan>. "Pure Alcohol (Ethanol)." Pharmacology Company. N.p., n.d. Web. 30 Jan. 2011.      <http://www.pharmco-prod.com/pages/ep1.pdf>. Seida, Caitlin. "How Alcohol Kills Bacteria." Associated Content from Yahoo. N.p., n.d. Web. 1 Dec. 2010. <http://www.associatedcontent.com/article/      2066479/how_alcohol_kills_bacteria.html>. Shakhashiri. "Ethanol." Science Fun. N.p., 5 Feb. 2009. Web. 29 Jan. 2011.      <http://scifun.chem.wisc.edu/chemweek/pdf/ethanol.pdf>.