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 inhibit the growth of E. Coli and B. Cereus bacteria.

Research • Gram negative • Rod shaped facultative anaerobe • Most strains are harmless • Can cause food poisoning • Frequently used as a model organism • Gram positive • Rod shaped facultative anaerobe • Capable of forming spores • Known to cause food poisoning Escherichia Coli Bacillus Cereus 10% bleach in water solution is sufficient to effectively kill most bacteria. (Recommended amount by the CDC)

Hypothesis • If different bleach solutions are tested on bacteria, then the weakest solution of bleach in water that will effectively inhibit the growth of bacteria will be found and this will be the 10% solution.

Materials • Escherichia Coli bacteria • Bacillus Cereus bacteria • Bleach • Water • 16 agar plates • 48 sterile discs • Inoculating Loop • Forceps • Incubator • 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. • The dependent variable is the amount of bacteria growth inhibited. • 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 • Although the 10% solution did inhibit the growth of both forms of bacteria, it was not the weakest solution to have an effect. • 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