Bacteria Growth in Refrigerated vs. Non- Refrigerated Ground Beef Biology 110 October 27, 2005 Liz Ringler Fouzia Abidi

Escherichia coli (E. coli) E. coli are bacteria most commonly found in the intestines of humans and animals. E. coli are bacteria most commonly found in the intestines of humans and animals. Although most E. coli stains are harmless the E. coli O157:H7 is harmful to humans. Although most E. coli stains are harmless the E. coli O157:H7 is harmful to humans. In some cases E. coli O157:H7 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.). In some cases E. coli O157:H7 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 O157:H7 is most harmful to young children and the elderly. E. coli O157:H7 is most harmful to young children and the elderly. Most E. coli live symbiotically with us; ex. they help digest our food 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. 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.

E. coli How is E. coli O157:H7 spread? How is E. coli O157:H7 spread? The harmful strain or E. coli O157:H7 is ingested into the body by eating contaminated food, most commonly rare or undercooked beef (E. coli, n.d.). The harmful strain or E. coli O157:H7 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.). 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.). 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.). It can also be spread person-to-person by hands are not washed after using the bathroom or diapering children (E. coli, n.d.).

E. coli and Binary Fission E. coli is a bacteria. E. coli is a bacteria. All bacteria reproduce through a process called binary fission All bacteria reproduce through a process called binary fission

Purpose 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 (2.5°C) Ground beef kept at refrigerated temperature (2.5°C) Determine at which temperature ground beef yields the most bacterial species diversity (colony types).

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 (22°C) will yield a greater bacterial diversity (colony types) than ground beef kept in a refrigerator at 2.5°C. Additionally, the type of agar used to culture bacteria growing in ground beef may play a key in studying bacterial species diversity.

Methods 1) Petri dishes and test tubes were labeled. 2) 1g of ground beef at room temperature was taken and a serial dilution was used to produce different concentrations, ranging from to ) 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). 4) Steps 3 and 4 were repeated for serially diluted concentrations of 1 g of refrigerated ground beef at to ) All Petri dishes were wrapped in Parafilm wrap and incubated for one 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.

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.

Ground Beef at Room Temperature(22°C) Tryptic Soy Agar A ColonyA F SizeU ShapeN MarginG SurfaceU ColorS

Ground Beef at Room Temperature(22°C) Tryptic Soy Agar ColonyAB Size5mm1.5mm Shaperound Marginsmooth Surfacecontoured Colorwhiteyellow A B

Ground Beef at Room Temperature(22°C) Tryptic Soy Agar A B ColonyAB F SizeU8mm ShapeNround MarginGconcentric SurfaceUsmooth ColorS yellow w/black dots

Ground Beef at Room Temperature(22°C) Nutrient Agar A ColonyA Size1mm Shaperound Marginsmooth Surfaceconcentric Colortan

Ground Beef at Room Temperature(22°C) Nutrient Agar A C B D ColonyABCD Size2mmpunctiformpuntiformpunctiform Shaperound irregular Marginsmooth lobateirregular Surfacesmooth wrinkled Coloryellow transparent white transparent

Ground Beef at Room Temperature(22°C) Nutrient Agar A BE D C ColonyABCDE Size5mm3mm5mm.5mm6mm Shaperound irregularround Marginsmooth smooth /irregularsmooth round Surfaceconcentricsnoothsmooth Color white w/ yellow dotyellowcream clear/ white yellow/ transparent

Ground Beef Refrigerated at 2.5°C Typtic Soy Agar No Bacterial Colonies Were Observed

Ground Beef Refigerated at 2.5°C Typtic A B E D C ColonyABCDE F SizeU5mm3.5mm3mm2mm ShapeN round/ irregularround MarginG round/ lobatesmooth SurfaceUsmoothconcentricsmooth ColorSwhite yellowwhite

Ground Beef Refigerated at 2.5°C Typtic Soy Agar A B C ColonyABC F SizeU3mm ShapeN round/ irregular MarginGlobate smooth/ lobate SurfaceUsmooth concentric/ smooth ColorSwhite transparent outside, solid tan inside

Ground Beef Refrigerated at 2.5°C Nutrient Soy Agar A ColonyA Sizepunctiform Shaperound Marginround Surfacewrinkled Colorwhite/ transparent

Ground Beef Refigerated at 2.5°C Nutrient Soy Agar A ColonyA Size2mm Shaperound Marginsmooth Surfacesmooth Colorwhite/yellow

Ground Beef Refigerated at 2.5°C Nutrient Soy Agar No Bacterial Colonies Were Observed

Figures

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.

References Campbell, Neil A., and Jane B. Reese. Biology: 7 th Edition. New York: Benjamin/Cummings Publishing Co., Inc Morgan, I.G., and Brown Carter, M.E., Investigating Biology: A Laboratory Manual for Biology. California: Benjamin/Cummings Publishing Co., Inc E. coli. (n.d.). Retrieved October 28, 2005, from Topics/ecoli.htm Communicable Diseases and Epidemiology Escherichia coli O157:H7 (E. coli) fact sheet. (n.d.). Retrieved October 28, 2005, from metrokc.gov/health/prevcont/ecoli.htm