Bacteria Growth in Refrigerated vs. Non-Refrigerated Ground Beef

1
Bacteria Growth in Refrigerated vs.
Non-Refrigerated Ground Beef

• Biology 110
• October 27, 2005
• Liz Ringler
• Fouzia Abidi

2
Escherichia coli (E. coli)

• E. coli are bacteria most commonly found in the
  intestines of humans and animals.
• Although most E. coli stains are harmless the E.
  coli O157H7 is harmful to humans.
• In some cases E. coli O157H7 causes a
  complication that damages the kidneys called
  hemolytic uremic syndrome, or HUS. This is most
  common in young children and the elderly
  (Communicable, n.d.).
• E. coli O157H7 is most harmful to young children
  and the elderly.
• Most E. coli live symbiotically with us ex. they
  help digest our food
• The presence of E. coli and many other kinds of
  bacteria inside our intestines aids in the
  digestion of cellulose and produces essential
  vitamins, such as Vitamin K and Vitamin B-
  complex.

3
E. coli

• How is E. coli O157H7 spread?
• The harmful strain or E. coli O157H7 is ingested
  into the body by eating contaminated food, most
  commonly rare or undercooked beef (E. coli,
  n.d.).
• This bacteria lives in the intestine of cattle
  and contaminates the meat during the slaughtering
  process (E. coli, n.d.).
• Fresh vegetable, unpasteurized fruit juice and
  raw milk can also cause outbreaks (E. coli,
  n.d.).
• It can also be spread person-to-person by hands
  are not washed after using the bathroom or
  diapering children (E. coli, n.d.).

4
E. coli and Binary Fission

• E. coli is a bacteria.
• All bacteria reproduce through a process called
  binary fission

5
Purpose

• Examine the bacterial colonies found in
• Ground beef kept at room temperature (22C)
• Ground beef kept at refrigerated temperature
  (2.5C)
• Determine at which temperature ground beef yields
  the most bacterial species diversity (colony
  types).

6
Hypothesis

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

7
Methods

• Petri dishes and test tubes were labeled.
• 1g of ground beef at room temperature was taken
  and a serial dilution was used to produce
  different concentrations, ranging from 10-2 to
  10-7.
• The Streak Plate method was used to inoculate
  two Petri dishes, one with nutrient agar and the
  other with tryptic soy agar, for each
  concentration produced through the serial
  dilution process (Figure 1).
• Steps 3 and 4 were repeated for serially diluted
  concentrations of 1 g of refrigerated ground beef
  at 10-3 to
• 10-5.
• 5) All Petri dishes were wrapped in Parafilm
  wrap and incubated for one week at 27C.

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.
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Control

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

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Ground Beef 10-6 at Room Temperature(22C)Tryptic
Soy Agar
Colony A
F
Size U
Shape N
Margin G
Surface U
Color S
A
10
Ground Beef 10-7 at Room Temperature(22C)
Tryptic Soy Agar
Colony A B
Size 5mm 1.5mm
Shape round round
Margin smooth smooth
Surface contoured contoured
Color white yellow
A
B
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Ground Beef 10-8 at Room Temperature(22C)
Tryptic Soy Agar
Colony A B
F
Size U 8mm
Shape N round
Margin G concentric
Surface U smooth
Color S yellow w/black dots
A
B
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Ground Beef 10-6 at Room Temperature(22C)Nutrien
t Agar
Colony A
Size 1mm
Shape round
Margin smooth
Surface concentric
Color tan
A
13
Ground Beef 10-7 at Room Temperature(22C)
Nutrient Agar
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 white transparent white transparent
D
B
C
A
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Ground Beef 10-8 at Room Temperature(22C)
Nutrient Agar
Colony A B C D E
Size 5mm 3mm 5mm .5mm 6mm
Shape round round irregular round round
Margin smooth smooth/irregular smooth smooth round
Surface concentric snooth smooth smooth smooth
Color white w/yellow dot yellow cream clear/white yellow/transparent
A
D
C
B
E
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Ground Beef 10-3 Refrigerated at 2.5CTyptic Soy
Agar
No Bacterial Colonies Were Observed
16
Ground Beef Refigerated at 2.5CTyptic 10-4
Colony A B C D E
F
Size U 5mm 3.5mm 3mm 2mm
Shape N round/irregular round round round
Margin G round/lobate smooth smooth smooth
Surface U smooth concentric smooth smooth
Color S white white yellow white
D
E
C
B
A
17
Ground Beef 10-5 Refigerated at 2.5CTyptic Soy
Agar
Colony A B C
F
Size U 3mm 3mm
Shape N round/irregular round/irregular
Margin G lobate smooth/lobate
Surface U smooth concentric/smooth
Color S white transparent outside,solid tan inside
A
B
C
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Ground Beef 10-3 Refrigerated at 2.5CNutrient
Soy Agar
Colony A
Size punctiform
Shape round
Margin round
Surface wrinkled
Color white/ transparent
A
19
Ground Beef 10-4 Refigerated at 2.5CNutrient
Soy Agar
Colony A
Size 2mm
Shape round
Margin smooth
Surface smooth
Color white/yellow
A
20
Ground Beef 10-5 Refigerated at 2.5CNutrient
Soy Agar

• No
• Bacterial
• Colonies
• Were
• Observed

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Figures
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Conclusion

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

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References

• Campbell, Neil A., and Jane B. Reese. Biology
  7th Edition. New York Benjamin/Cummings
  Publishing Co., Inc. 2005.
• Morgan, I.G., and Brown Carter, M.E.,
  Investigating Biology A Laboratory Manual for
  Biology. California Benjamin/Cummings Publishing
  Co., Inc. 1993.
• E. coli. (n.d.). Retrieved October 28, 2005, from
  http//www.doh.wa.gov/ Topics/ecoli.htm
• Communicable Diseases and Epidemiology
  Escherichia coli O157H7 (E. coli) fact sheet.
  (n.d.). Retrieved October 28, 2005, from
  http//www. metrokc.gov/health/prevcont/ecoli.htm