Coffee’s Effect on the Population of Escherichia coli

David McFall

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.

Coffee

•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

Brands Tested

20 mg of Caffeine per ounce 0.6 to 1.4 mg of Caffeine per ounce

Starbucks X-bold Sumatra Roast (Coffee A) Starbucks Decaf House Blend (Coffee B)

Escherichia coli

The model for this experiment is Escherichia coli (E. coli).

It is found in the intestinal tract of most animals, including humans.

Most importantly, E. coli has been tested in conjunction with caffeine before in previous studies.

Previous Studies

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.

Purpose:

To determine the effect of coffee on human coli form populations.

Hypotheses:

Null Hypothesis: Neither caffeinated nor decaffeinated coffee will have an

effect on the population of E. coli at any concentration.

Alternative Hypothesis: Caffeinated and decaffeinated coffee will

significantly effect survivorship of E. coli

Materials:

E. coliPermanent MarkerLatex GlovesMicropipettesMicrotubesCaffeinated CoffeeDecaffeinated CoffeeSterile Distillation Fluid58 LB agar plates (Per Liter:1% Tryptone, 0.5% Yeast Extract, and 1% NaCl)LB mediaKlett Spectrophotometer0.22 micron syringe filters2 Sterile FiltersBunsen BurnersSpread BarIncubatorEthanolMatchesVortex

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 (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 of SDFto create coffee concentrations of 10%, 1%, and 0.1%.

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.

Procedure: (Infused Plates)

1. Repeat steps 1-6 in the Preliminary Procedure.2. Both brands of coffee were brewed as directed.3. The coffee was then sterile filtered.4. 200 µL of sterile coffee were removed from the

tubes and spread on LB plates.

5. The plates were incubated at 37 degrees for 24 hours.

6. 100uL of bacteria (control tube) was spread onto each plate.

7. The resulting colonies were counted visually. Each colony was assumed to have arisen from one cell.

8. The appropriate statistical analyses were performed to adequately assess the hypothesis.

Table 1 Control (x2) .01x (x4) .1x (x4) x (x4)

E. coli .1 ml .1 ml .1 ml .1 ml

Sterile Distillation Fluid 9.9 ml 9.89 ml 9.8 ml 8.9 ml

Coffee 0 ml .01 ml .1 ml 1 ml

Total Volume 10 ml 10 ml 10 ml 10 ml

Chart of Concentration

Contro

l.0

1x .1x x

Decaff

eina

ted

Caffei

nate

d 0

100

200

300

400

500

600

700 Average Effect of Coffee on E. coli

ControlDecaffeinatedCaffeinatedInfused Plates

Concentrations

Colo

nie

s o

f E.

coli

P<0.05

P<0.05

P<0.05

P<0.05 P>0.0

5

P>0.05

P>0.05

Dunnett’s Test Analysis

T Critical= 3.49 (Significant)

Variable Concentration T Value Interpretation .01x CAFF 2.2 Insignificant .1x CAFF 3.46 Insignificant x CAFF 4.78 Significant .01x DCAFF 7.63 Significant .1x DCAFF 4.54 Significant x DCAFF 3.69 Significant

Conclusions:

Caffeinated coffee significantly increased the population of E. coli, but only in the 10% concentration.

Decaffeinated coffee significantly increased the population of E. coli in all concentrations.

Future Changes:

Test more brands of coffee

Use a different model

Test coffee in conjunction with other caffeinated beverages, such as tea or energy drinks

Difficulties Encountered:

Plating was not exactly synchronized, which could have resulted in extra time for bacterial replication. A team of students could remedy this technical problem.