The Effect of Bleach on Bacteria

The Effect of Bleach on Bacteria Bailey McCue Grade 9

Problem • The purpose of this experiment was to find the weakest solution of bleach in water that would effectively kill E. Coli and B. Cereus bacteria.

Research • Gram negative • Rod shaped facultative anaerobe • Most strains are harmless • Gram positive • Rod shaped facultative anaerobe • Can cause food poisoning 10% bleach in water solution is sufficient to effectively kill most bacteria. (Recommended amount by the CDC) Escherichia Coli Bacillus Cereus

Hypothesis • If different bleach solutions are tested on bacteria, then the weakest solution of bleach in water that will effectively kill bacteria will be found.

Materials • Escherichia Coli bacteria • Bacillus Cereus bacteria • Bleach • Water • 16 agar plates • 48 sterile discs • Inoculating Loop • Forceps • Ruler • Marker • Tape

Procedure • 1. Prepare solutions of 0.5%, 1%, 3%, 5%, 8%, 10%, and 15% bleach in water. • 2. Label each of the agar plates with the solution and the bacteria to be tested. • 3. Inoculate 8 plates with E. Coli and 8 plates B. Cereus using the inoculating loop. • 4. Hold a single sterile disc with the forceps, dip it into a bleach solution, then place it in corresponding agar plate. Do this three times for each bleach solution. • 5. Place all plates in an incubator and allow to incubate over night. • 6. Examine all plates and using a ruler with mm, measure the zones of inhibition. • 7. Safely dispose of all plates.

Variables • The independent variable is the strength of the bleach solution used. (bacteria?) • The dependent variable is the amount of bacteria killed. • The constants are the amount of bacteria, amount of solution applied to each sample, temperature, time, type of bacteria and type of bleach. • The controls were the agar plates with the sterile discs soaked in water

Results

Conclusion • The results of this experiment supported my hypothesis that the if different bleach solutions are tested on bacteria, then the weakest solution of bleach in water that will effectively kill bacteria will be found. • The weakest solution of bleach in water to effectively kill bacteria was the 3% solution. Anything below this solution was ineffective.

Thank You “About E. Coli. Marler Clark, n.d. Web. 22 Feb. 2010. <http://www.about-ecoli.com/>. "Bacillus Cereus." Online Textbook of Bactriology. N.p., n.d. Web. 24 Feb. 2010. <http://www.textbookofbacteriology.net/B.cereus.html>. "Clorox Regular Bleach." Clorox . N.p., n.d. Web. 24 Feb. 2010. <http://www.clorox.com/products/faqs.php?prod_id=clb>. "Escherichia Coli." Centers For Disease Control and Prevention. N.p., n.d. Web. 24 Feb. 2010. <http://www.cdc.gov/nczved/dfbmd/disease_listing/ stec_gi.html#1>. "Is Bleach A Good Disinfectant?" Science in The Real World: Microbes in Action. N.p., n.d. Web. 24 Feb. 2010. <http://www.umsl.edu/~microbes/pdf/ bleach.pdf>. • Thank you for listening to my presentation. Are there any questions?

The Effect of Bleach on Bacteria