The Effect of Saliva on Bacteria Mackenzie Abate 9 th Grade

Problem/Rationale Does saliva have an effect on bacteria? If so, what is this effect? The reason I wanted to do this project was because I wanted another opportunity to work with bacteria. I find it very interesting. Also, I have always heard people say “a dog’s mouth is cleaner than a human’s.” By testing the saliva’s effect on bacteria, I tested the cleanliness of the mouth.

Research E. coli Gram negative Motile Facultative anaerobe Heterotrophic Mixed acid fermentation: lactate, succinate, ethanol, carbon dioxide and acetate Conjugation, transformation and transduction B. cereus Gram positive Facultative anaerobe Endospore forming From maltose, glucose and salicin fermentation, acid is made. Two types of food poisoning

Research S. mutans Gram positive Nonmotile Metabolizes sucrose to lactic acid Beta-hemolytic Allowed to grip to teeth because of receptors Found mainly on teeth S. epidermidis Gram positive Nonmotile Facultative anaerobe Grows on plastic objects in body Ferments maltose, not xylose, sucrose or trehelose.

Research Saliva – 98% water – Two main enzymes: Lysozyme: antibacterial Amylase: digestion – Oral Hygiene: teeth and mouth; residue, particles, and epithelial tissue.

Research Amylase – Enzyme – breaks down carbs from polysaccharides to disaccarides Lysozyme – Enzyme – “lyses” certain bacteria; breaks down cell walls; rinses away energy sources

Hypothesis If varied types of saliva are used on bacteria, then human saliva will have the most inhibitory effect on the bacteria.

Materials Bacteria: E. coli, B. cereus, S. mutans and S. epidermidis Amylase Lysozyme Additional Materials – Blank disks – Plates of agar – Innoculating loop – Autoclave – Matches – Incubator – Disposable gloves – Safety goggles

Procedure Saliva will be extracted 2 tabs will be soaked in each saliva type 2 tabs will be soaked in amylase 2 tabs will be soaked in water 2 tabs will remain blank The E. coli and B. cereus will be plated using sterile technique The tabs will then be added to the bacterial plates The plates will be sealed and stored at 37 degrees Celsius Bacterial growth will be observed over the period of 3 days The zone of inhibition will be measured

Procedure II Saliva will be extracted 2 tabs will be soaked in each saliva type 2 tabs will be soaked in water 2 tabs will remain blank The S. mutans and S. epidermidis will be plated using sterile technique The tabs will then be added to the bacterial plates The plates will be sealed and stored at 37 degrees Celsius Bacterial growth will be observed over the period of 3 days The zone of inhibition will be measured

Procedure (cont’d) I furthered my research and discovered that the enzyme lysozyme is the enzyme in saliva that breaks down bacteria. – 2 tabs will be soaked in water – 2 tabs will remain blank – All four types of bacteria will be plated again using sterile technique. – Plates will be sealed and stored and 37 degrees Celsius – Bacterial growth will be observed over a period of three days – The zone will be measured on the third day

Data

Conclusion My hypothesis stated that if three different types of saliva were used to inhibit bacterial growth, then human saliva would be the most effective in doing so. This hypothesis was not supported by the data because saliva’s inhibitory effect was equivalent to that of water.

Conclusion What went wrong – A fungus grew on a few of the plates. It possibly came from the air or careless sterile technique. Improvements – More careful with sterile technique, the bacteria and tabs.

Thank you! National Center for Biotechnology Information. N.p., Oct Web. 30 Nov Leboffe, Michael J., and Burton E. Pierce. A Photographic Atlas for the Microbiology Laboratory. Englewood: Morton Publishing, n.d. Print. Sherwood, Lauralee. Human Physiology. N.p.: Thomson, n.d. Print. Tenovuo ‌, Jorma. "Antimicrobial function of human saliva - how important is it for oral health?" Informahealthcare.com. N.p., n.d. Web. 30 Nov Any questions?