Antimicrobial Effects of
Human Saliva
Steven Esposito
Pittsburgh Central Catholic High School
Defense Systems of the Body

The immune system is comprised of smaller more specific systems
called defense systems.

Each defense system has a small line of jobs that it carries out.

There are ten main defense systems in the body.
Defense Systems
Defense System
Epithelial surface
Mucosal surface
Lysozyme
Phagocytic cells
Ciliated cells
Fatty acids
Stomach Acid
Normal bacterial flora
Urine excretion
Complement system
Action
Physical barrier prevents pathogen entry
Traps bacteria
Dissolves peptidoglycan
Ingests and destroys pathogens
Moves pathogens away from body
Prevents bacterial growth
Destruction of ingested pathogens
Competes with pathogens
Removes pathogens from body
Mediates phagocytes function
Three Major Salivary Glands



Saliva is a key part of the immune system.
Without it we would be more prone to infection from harmful microbes.
Human saliva is produced by three pairs of major slavery glands
Name
Type Saliva Secreted
Parotid
Saliva with a watery serous consistency
Sublingual and minor slavery glands
Viscous mucous fluid
Submandibular gland
Mixture of watery and viscous fluid
Human Saliva


Is composed mostly of water, about 98-99 percent.
Has a very minuscule amount of electrolytes, mucus,
antibacterial compounds (thiocyanates, hydrogen
peroxide, and secretory immunoglobulin A)
Antibacterial Compounds in Saliva
Secretory immunoglobulin A


Neutralizes bacteria, and enzyme toxins.
Serves as an antibody for bacterial antigens, aggregates bacteria,
inhibits oral tissues adherence.
Thiocyanates

Antimicrobial chemical compounds (SCN)
Hydrogen Peroxide


A weak acid.
Hydrogen peroxide is naturally produced as a byproduct of oxygen
metabolism.
2 Major Enzymes In Saliva
Name
Function
a-amylase
Digests starch and lipid fats in food
Lysozyme
Acts to cause lysis in bacteria
Escherichia coli

A prokaryotic, unicellular,
bacterial cell which can
most frequently be found in
the large intestine of
endothermic animals.

The most studied
prokaryote on earth.

E. coli are a large and
diverse group of bacteria.

Some strands can make one
very sick, causing diarrhea,
while others can cause
urinary tract infections.
Purpose
To assess the effects of various concentrations of
human saliva on the survivorship of E. coli.
Null Hypothesis and Alternative
Hypothesis


The saliva will not significantly effect E. coli
survivorship.
The saliva will significantly effect E. coli
survivorship enough to conclude that saliva is
antimicrobial.
1. Pipettes
2. DH5 Alpha E-Coli
3. 40 LB Agar Plates
Materials
4. Sterile Pipette Tips
5. Spreader Bars
6. Saliva (My Own)
7. 0.22 micron Sterile Filter
8. SDF ( Sterile Dilution Fluid)
9. Test Tubes
10. Incubator
11. Bunsen Burner
12.LB media (0.55 Yeast extract, 1% Tryptone, 1% Sodium Chloride)
13.1.5ml micro-centrifuge.
Procedure
1.
E. coli was grown overnight in sterile LB media.
2.
A Sample of the overnight culture was added to fresh media
in a sterile sidearm flask.
3.
The culture was placed in an incubator at 37°C until a cell
density of 50 Klett spectrophotometer units were reached.
This represents cell densities of approximately 108 cells/mL.
4. The culture was diluted in sterile dilution fluid to a
concentration of approximately 105 cells/mL.
Procedure
5.
Human saliva (my own) was collected and sterile filtered by
means of a 0.22 micron syringe filter.
6.
The following components were pipetted into sterile 1.5mL
micro-centrifuge tubes.
7.
The tubes were allowed to incubate for 15 minutes before plating.
8.
After exposure to saliva 0.1 mL aliquots of cell suspensions were
plated onto nutrient agar.
9.
Incubated agar plates for 24 hours.
10. Counted the colonies of bacteria on the plates.
Concentration of Saliva
Saliva
0 mL
.01 mL
SDF
0.99 mL
0.89 mL 0.49 mL 0 mL
Microbe
0.01 mL
0.01 mL 0.01 mL 0.01 mL
Final
0%
Concentration Saliva
10%
Saliva
.05 mL
50%
Saliva
0.99 mL
99%
Saliva
Average Microbial Survivorship
P-value
3.65E-11
Number of
Colonies
450
400
350
300
250
200
150
100
50
0
0%
Saliva
29.49
26.38
10%
Saliva
50%
Saliva
Concentration of Saliva
25.23
99%
Saliva
Dunnett's Test

Dunnett’s Test purpose- to determine if there
is a significant or insignificant variation
between the variable groups and the control
group.
Dunnett's Test
T-critical= 2.76
T-critical
α= .05
10% Saliva vs.
0% Saliva
29.49
Very Significant
50% Saliva vs.
0% Saliva
26.38
Very Significant
99% Saliva vs.
0% saliva
25.23
Very Significant
Conclusions

The data appeared to be significant enough to reject the null
hypothesis.

The alternative hypothesis was accepted. The saliva will
significantly effect E. coli survivorship enough to
conclude that saliva is antimicrobial


When data was analyzed the 10% concentration of saliva
inhibited microbial growth the most, with 50% and 99%
coming in second and third respectively.
After data was analyzed results showed that the survivorship
of the E. coli was reduced by about 75%.
Limitations and Extensions
Limitations

Some lag time when plating could have resulted in extra cell
replication prior to
Extensions




Saliva from different species could be utilized to see if other
species saliva also has antimicrobial qualities.
Vary the time the saliva samples were exposed to the microbe
before plating.
Synchronize cell plating.
Utilize different microbial models.
Sources

http://www.newworldencyclopedia.org/entry/Saliva

http://digestivesystem.suite101.com/article.cfm/the_
many_purposes_of_saliva

http://www.thejcdp.com/issue039/de_almeida/de_alm
eida.pdf