David McFall
Coffee
•Americans
consume 400
million cups of
coffee per year.
•Coffee has a high
caffeine content due to
its high concentration
in its endosperm.
•Coffee can be
decaffeinated by a
treatment of
methylene chloride.
The Effects of Coffee
Coffee’s side effects are
drawn from the release
of the hormone
epinephrine, shown
here.
The most notable
effects include:
high heart beat
high blood pressure
 higher blood sugar
content
 tense muscles
Epinephrine
How caffeine
interacts with the
body
The binding of the
hormone adenosine to an
adenosine receptor in the
brain brings about sleep.
Caffeine blocks adenosine
from being connected to
the adenosine receptor.
The hormone epinephrine
is then produced. This
creates the notable effects
of caffeine.
Starbucks X-bold Sumatra Roast (CAFF)
20 mg of Caffeine per ounce
Starbucks Decaf House Blend (DCAFF)
0.6 to 1.4 mg of Caffeine per ounce
Escherichia coli
Escherichia coli is a large and
diverse group of gram (-) bacteria.
It is found in the intestinal tract
of most animals, including
humans.
E. coli has been tested in
conjunction with caffeine before
in previous studies.
Estimated to cause infection in
more than 70,000 patients a year
in the United States.
A
study from the Lithuanian State Science and Studies
Foundation concluded that when in high concentration, caffeine
lowers the population of E. coli.
Another study from the Indiana University School of Medicine
supported the previous study.
To determine the effect of coffee on human coliform
populations.
Null Hypothesis: Neither caffeinated nor decaffeinated coffee will
have a significant effect on the survivorhip of E. coli
at any concentration.
Alternative Hypothesis:
E. coli (DH5-alpha)
Klett Spectrophotometer
Latex Gloves
Micropipettes
Micro tubes
Starbucks X-bold Sumatra Roast
Starbucks Decaf House Blend
Sterile Dilution Fluid (SDF) (per 1 liter) (100mM KH2PO4, 100mM K2HPO4, 10mM
MgSO4, 1mM NaCl)
58 LB agar plates
LB media (Per Liter:1% Tryptone, 0.5% Yeast Extract, and 1% NaCl)
2 2 micron syringe Sterile Filters
Bunsen Burners
Spread Bar
Incubator
Ethanol
Matches
Vortex
1. E. coli was grown overnight in sterile LB agar.
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 (37°C) until a density of 50 Klett
spectrophotometer units was reached. This represents a cell density of approximately
108 cells/mL.
4. The culture was diluted in sterile dilution fluid to a concentration of approximately 105
cells/mL.
5. Caffeinated and decaffeinated coffee was mixed with the appropriate amount Sterile
Distillation Fluid to create coffee concentrations of 10%, 1%, and .1%.
6. 100 µL of cell culture was then added to the solutions, yielding a final volume of 10 mL
and a cell density of approximately 103 cells/mL.
7. The solutions were vortexed and allowed to sit at room temperature for 15 minutes.
8. 100 µL aliquots were removed from the tubes and spread on LB plates.
9. The plates were incubated at 37 degrees for 24 hours.
10. The resulting colonies were counted visually. Each colony was assumed to have arisen
from one cell.
11. The appropriate statistical analyses were performed to adequately assess the
hypothesis.
1.
2.
3.
4.
5.
6.
7.
8.
Repeat steps 1-6 in the Preliminary Procedure.
Both brands of coffee were brewed as directed.
The coffee was then sterile filtered.
200 µL of sterile coffee were removed from the tubes and
spread on LB plates. The plates were inverted and incubated
for 30 minutes to allow absorption.
100uL of E. coli (control tube) was spread onto the plates.
The plates were incubated at 37 degrees for 24 hours.
The resulting colonies were counted visually. Each colony
was assumed to have arisen from one cell.
The appropriate statistical analyses were performed to
adequately assess the hypothesis.
Chart of Concentration
Table 1
Control
.01x
.1x
x
E. coli
0.1 ml
0.1 ml
0.1 ml
0.1 ml
Sterile Dilution Fluid
(SDF)
9.9 ml
9.89 ml
9.8 ml
8.9 ml
Coffee
0 ml
0.01 ml
0.1 ml
1 ml
Total Volume
10 ml
10 ml
10 ml
10 ml
Coffee Effects on E. coli Survivorship
700
Colonies of E. coli
600
500
400
300
Control
Decaffeinated
200
Caffeinated
Infused Plates
100
0
Concentrations
T Critical= 3.49 (Significant)
Variable
Concentration
.01x CAFF
.1x CAFF
x CAFF
.01x DCAFF
.1x DCAFF
x DCAFF
T Value
2.2
3.46
4.78
7.63
4.54
3.69
Interpretation
Insignificant
Insignificant
Significant
Significant
Significant
Significant
Did liquid exposure to caffeine significantly effect survivorship?
P-Value 7.29E-8 Significant
Which caffeine exposures significantly effected survivorship?
10% Exposure- T-Value 4.78 Significant
Did caffeinated coffee vary from decaffeinated in survivorship?
0.1% CAFF-P-Value 1.41E-3 Significant
1% CAFF-P-Value 0.28
Insignificant
10% CAFF-P-Value 0.62
Insignificant
Did continuous exposure to coffee (Infused Plates) alter survivorship?
CAFF-P-Value 0.57
Insignificant
DCAFF-P-Value 0.46
Insignificant
It seems as if caffeinated coffee increased the
population of E. coli, but only in the 10%
concentration.
Decaffeinated coffee, on the other hand, seemed
to increase the population of E. coli in all
concentrations.
Plating
was not exactly synchronized(10 minute
lag), which could have resulted in extra time for
bacterial replication. A team of students could
remedy this technical problem.
Test more brands of coffee
Use a different model
Test coffee in conjunction with other caffeinated
beverages, such as tea or energy drinks
Investigate coffee’s ability to recover from stress.
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