Bacteria Growth in Bacteria Growth in Refrigerated vs. Non-Refrigerated vs. Non-

Refrigerated Ground BeefRefrigerated Ground BeefBiology 110Biology 110

October 27, 2005October 27, 2005

Liz Ringler Liz Ringler Fouzia AbidiFouzia Abidi

Escherichia coli (E. coli)Escherichia coli (E. coli)• E. coliE. coli are bacteria most commonly found are bacteria most commonly found

in the intestines of humans and animals.in the intestines of humans and animals.• Although most Although most E. coliE. coli stains are harmless stains are harmless

the the E. coliE. coli O157:H7 is harmful to O157:H7 is harmful to humans.humans.

• In some cases In some cases E. coli E. coli O157:H7 causes a O157:H7 causes a complication that damages the kidneys complication that damages the kidneys called hemolytic uremic syndrome, or called hemolytic uremic syndrome, or HUS. This is most common in young HUS. This is most common in young children and the elderly (Communicable, children and the elderly (Communicable, n.d.).n.d.).

• E. coliE. coli O157:H7 is most harmful to young O157:H7 is most harmful to young children and the elderly.children and the elderly.

• Most Most E. coliE. coli live symbiotically with us; ex. live symbiotically with us; ex. they help digest our food they help digest our food

• The presence of The presence of E. coliE. coli and many other and many other kinds of bacteria inside our intestines kinds of bacteria inside our intestines aids in the digestion of cellulose and aids in the digestion of cellulose and produces essential produces essential vitamins, such as vitamins, such as Vitamin K and Vitamin B- complex.Vitamin K and Vitamin B- complex.

E. coliE. coli

How is E. coli How is E. coli O157:H7 O157:H7 spread?spread?

• The harmful strain or The harmful strain or E. coliE. coli O157:H7 O157:H7 is ingested into the body by eating is ingested into the body by eating contaminated food, most commonly contaminated food, most commonly rare or undercooked beef (rare or undercooked beef (E. coliE. coli, , n.d.)n.d.)..

• This bacteria lives in the intestine of This bacteria lives in the intestine of cattle and contaminates the meat cattle and contaminates the meat during the slaughtering process (during the slaughtering process (E. E. colicoli, n.d.), n.d.)..

• Fresh vegetable, unpasteurized fruit Fresh vegetable, unpasteurized fruit juice and raw milk can also cause juice and raw milk can also cause outbreaks (outbreaks (E. coliE. coli, n.d.), n.d.)..

• It can also be spread person-to-person It can also be spread person-to-person by hands are not washed after using by hands are not washed after using the bathroom or diapering children (the bathroom or diapering children (E. E. colicoli, n.d.), n.d.)..

E. coliE. coli and Binary Fission and Binary Fission

• E. coliE. coli is a bacteria. is a bacteria.

• All bacteria reproduce All bacteria reproduce through a process through a process called binary fissioncalled binary fission

PurposePurpose

Examine the bacterial colonies found in:Examine the bacterial colonies found in:• Ground beef kept at room temperature (22°C)Ground beef kept at room temperature (22°C)• Ground beef kept at refrigerated temperature Ground beef kept at refrigerated temperature

(2.5°C)(2.5°C)

Determine at which temperature ground Determine at which temperature ground beef yields the most bacterial species beef yields the most bacterial species diversity (colony types).diversity (colony types).

HypothesisHypothesis

Bacteria grows at a more rapid rate when Bacteria grows at a more rapid rate when temperature is warmer (Campbell and Reese, temperature is warmer (Campbell and Reese, 2005). Using temperature a the variable in the 2005). Using temperature a the variable in the experiment, the ground beef kept at room experiment, the ground beef kept at room temperature (22°C) will yield a greater bacterial temperature (22°C) will yield a greater bacterial diversity (colony types) than ground beef kept in diversity (colony types) than ground beef kept in a refrigerator at 2.5°C. Additionally, the type of a refrigerator at 2.5°C. Additionally, the type of agar used to culture bacteria growing in ground agar used to culture bacteria growing in ground beef may play a key in studying bacterial beef may play a key in studying bacterial species diversity.species diversity.

MethodsMethods1)1) Petri dishes and test tubes were Petri dishes and test tubes were

labeled. labeled. 2)2) 1g of ground beef at room 1g of ground beef at room

temperature was taken and a serial temperature was taken and a serial dilution was used to produce different dilution was used to produce different concentrations, ranging from 10concentrations, ranging from 10 -2-2 to to 1010-7.-7.

3)3) The “Streak Plate method” was used The “Streak Plate method” was used to inoculate two Petri dishes, one to inoculate two Petri dishes, one with nutrient agar and the other with with nutrient agar and the other with tryptic soy agar, for each tryptic soy agar, for each concentration produced through the concentration produced through the serial dilution process (Figure 1). serial dilution process (Figure 1).

4)4) Steps 3 and 4 were repeated for Steps 3 and 4 were repeated for serially diluted concentrations of 1 g serially diluted concentrations of 1 g of refrigerated ground beef at 10of refrigerated ground beef at 10 -3-3 to to 1010-5-5..

5) 5) All Petri dishes were wrapped in All Petri dishes were wrapped in Parafilm wrap and incubated for one Parafilm wrap and incubated for one week at 27°C.week at 27°C.

a. b. c.

Figure 1.

The Streak Plate Method. (a) Streak the dish straight across (b) Turn the dish 90° and continue streaking straight across and towards the center of the dish. (c) Turn the dish another 90° continue streaking until the entire dish is covered.

ControlControl

Two unopened Petri dishes, one containing Two unopened Petri dishes, one containing nutrient agar and the other containing tryptic soy nutrient agar and the other containing tryptic soy agar, to rule out the possibility of contamination agar, to rule out the possibility of contamination of the agars.of the agars.

Ground Beef 10Ground Beef 10-6-6 at Room at Room Temperature(22°C)Temperature(22°C)Tryptic Soy Agar Tryptic Soy Agar

A

Colony A

F

Size U

Shape N

Margin G

Surface U

Color S

Ground Beef 10Ground Beef 10-7-7 at Room at Room Temperature(22°C) Temperature(22°C)

Tryptic Soy AgarTryptic Soy Agar

Colony A B

Size 5mm 1.5mm

Shape round round

Margin smooth smooth

Surface contoured contoured

Color white yellow

A B

Ground Beef 10Ground Beef 10-8-8 at Room at Room Temperature(22°C) Temperature(22°C)

Tryptic Soy AgarTryptic Soy Agar

AB

Colony A B

F

Size U 8mm

Shape N round

Margin G concentric

Surface U smooth

Color Syellow w/black dots

Ground Beef 10Ground Beef 10-6-6 at Room at Room Temperature(22°C)Temperature(22°C)

Nutrient AgarNutrient Agar

A

Colony A

Size 1mm

Shape round

Margin smooth

Surface concentric

Color tan

Ground Beef 10Ground Beef 10-7-7 at Room at Room Temperature(22°C) Temperature(22°C)

Nutrient AgarNutrient Agar

AC

B

D

Colony A B C D

Size 2mm punctiform puntiform punctiform

Shape round round irregular irregular

Margin smooth smooth lobate irregular

Surface smooth smooth wrinkled wrinkled

Color yellow

transparent

whitetransparent white transparent

Ground Beef 10Ground Beef 10-8-8 at Room at Room Temperature(22°C) Temperature(22°C)

Nutrient AgarNutrient Agar

A

BE

DC

Colony A B C D E

Size 5mm 3mm 5mm .5mm 6mm

Shape round round irregular round round

Margin smoothsmooth/irregular smooth smooth round

Surface concentric snooth smooth smooth smooth

Colorwhite w/yellow dot yellow cream

clear/white

yellow/transparent

Ground Beef 10Ground Beef 10-3-3 Refrigerated at 2.5°C Refrigerated at 2.5°CTyptic Soy AgarTyptic Soy Agar

No Bacterial Colonies Were Observed

Ground Beef Refigerated at 2.5°CGround Beef Refigerated at 2.5°CTyptic 10Typtic 10-4-4

A

B

E

D

C

Colony A B C D E

F

Size U 5mm 3.5mm 3mm 2mm

Shape Nround/irregular round round round

Margin Ground/lobate smooth smooth smooth

Surface U smooth concentric smooth smooth

Color S white white yellow white

Ground Beef 10Ground Beef 10-5-5 Refigerated at 2.5°C Refigerated at 2.5°CTyptic Soy AgarTyptic Soy Agar

A

BC

Colony A B C

F

Size U 3mm 3mm

Shape Nround/irregular

round/irregular

Margin G lobatesmooth/lobate

Surface U smoothconcentric/smooth

Color S white

transparent outside,solid tan inside

Ground Beef 10Ground Beef 10-3-3 Refrigerated at 2.5°C Refrigerated at 2.5°CNutrient Soy AgarNutrient Soy Agar

A

Colony A

Size punctiform

Shape round

Margin round

Surface wrinkled

Color white/ transparent

Ground Beef 10Ground Beef 10-4-4 Refigerated at 2.5°C Refigerated at 2.5°CNutrient Soy AgarNutrient Soy Agar

AColony A

Size 2mm

Shape round

Margin smooth

Surface smooth

Color white/yellow

Ground Beef 10Ground Beef 10-5-5 Refigerated at 2.5°C Refigerated at 2.5°CNutrient Soy AgarNutrient Soy Agar

No

Bacterial

Colonies

Were

Observed

FiguresFigures

Ground Beef at Room Temperature

0

1

2

3

4

5

6

Tryptic10-6

Tryptic10-7

Tryptic10-8

Nutrient10-6

Nutrient10-7

Nutrient10-8

Agar Type

Nu

mb

er o

f C

olo

nie

s F

ou

nd

Refrigerated Ground Beef

0

1

2

3

4

5

6

Tryptic10-3

Tryptic10-4

Tryptic10-5

Nutrient10-3

Nutrient10-4

Nutrient10-5

Agar TypeN

um

ber

of

Co

lon

ies

Fo

un

d

ConclusionConclusion

The ground beef kept at room temperature The ground beef kept at room temperature overall housed the most bacterial colony types, overall housed the most bacterial colony types, therefore exhibiting a greater species diversity. therefore exhibiting a greater species diversity. The data herein support the hypothesis tested The data herein support the hypothesis tested and suggest that Nutrient Agar may be a better and suggest that Nutrient Agar may be a better medium for beef bacterial culture. Further medium for beef bacterial culture. Further experimentation is necessary to obtain higher experimentation is necessary to obtain higher numbers of statistical analysis.numbers of statistical analysis.

ReferencesReferences

Campbell, Neil A., and Jane B. Reese. Campbell, Neil A., and Jane B. Reese. Biology: 7Biology: 7thth Edition Edition. New York: . New York: Benjamin/Cummings Publishing Co., Inc. 2005.Benjamin/Cummings Publishing Co., Inc. 2005.

Morgan, I.G., and Brown Carter, M.E., Morgan, I.G., and Brown Carter, M.E., Investigating Biology: A Laboratory Investigating Biology: A Laboratory Manual for BiologyManual for Biology. California: Benjamin/Cummings Publishing Co., Inc. . California: Benjamin/Cummings Publishing Co., Inc. 1993.1993.

E. coli. E. coli. (n.d.). Retrieved October 28, 2005, from http://www.doh.wa.gov/ (n.d.). Retrieved October 28, 2005, from http://www.doh.wa.gov/ Topics/ecoli.htmTopics/ecoli.htm

Communicable Diseases and Epidemiology Communicable Diseases and Epidemiology Escherichia coliEscherichia coli O157:H7 (E. coli) O157:H7 (E. coli) fact sheet. (n.d.). Retrieved October 28, 2005, from http://www. fact sheet. (n.d.). Retrieved October 28, 2005, from http://www. metrokc.gov/health/prevcont/ecoli.htmmetrokc.gov/health/prevcont/ecoli.htm