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Aquatic Thermal Tolerance of E.coli

Aquatic Thermal Tolerance of E.coli. J.R. Stragar Grade 9 Pittsburgh Central Catholic High School. E.coli. Escherichia coli ( E.coli ) is one of the most common forms of bacteria found in many environments including the intestinal tracts of many mammals.

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Aquatic Thermal Tolerance of E.coli

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  1. Aquatic Thermal Tolerance of E.coli J.R. Stragar Grade 9 Pittsburgh Central Catholic High School

  2. E.coli • Escherichia coli (E.coli) is one of the most common forms of bacteria found in many environments including the intestinal tracts of many mammals. • E.coli has also been utilized as the most studied prokaryote in biological research. • There are many of different strains of E.coli, most of which are non-pathogenic. However, there are strains which can produce fatal disease in humans and other mammals.

  3. E.coli Recent Outbreaks • One of the more recent outbreaks of E.coli has been the Taco Bell lettuce E.coli outbreak. •  As of Wednesday, December 13, 2006, 71 persons have become ill with Escherichia coli 0157:H7 associated with eating contaminated lettuce at Taco Bell restaurants in the northeastern United States. • Cases were reported to the CDC from five states: New Jersey (33), New York (22), Pennsylvania (13), Delaware (2) and South Carolina (1). • Of the 71 persons with illness, 48 have been confirmed as cases.

  4. E.coli in Different Temperatures • Aside from using drugs to treat an E.coli infection or preservatives to prevent E.coli contamination, many people have sought simpler remedies for reducing exposure to potentially pathogenic microbes. • E.coli is often transmitted in solution (water). • QUESTION: How does the temperature of the aquatic environment effect the survivorship of E.coli? • E.coli can grow in temperatures ranging from 7°C to 50°C, with an optimum temperature of 37°C. • It is destroyed by thorough cooking of foods until all parts reach a temperature of 70°C or higher. • 2 methods utilized to reduce the amount of bacteria in foods have been heating and cooling (refrigeration).

  5. Purpose • To examine the effect of water environment temperature on E.coli survivorship.

  6. Hypotheses • The 50° C water temperature will kill the most E.coli. • The null hypothesis is that temperature will have no effect on the survivorship of E.coli. • Increasing exposure time will result in a decrease in survivorship in all temperatures. • The other null is that incubation time will have no effect on survivorship of E.coli.

  7. Materials • 60 LB agar plates( 1 % tryptone, 5 % yeast extract, 1% NaCl, 1.5 % agar) • LB media (1 % tryptone, 5 % yeast extract, 1% NaCl) • Klett spectrophotometer • Sterile pipette tips • Micropipettors • 4 one liter beakers • Freezer • Vortex • Hot and cold tap water • Incubator • Sidearm flask • Spread plate • Spreader bar • Ethanol • 20 mL Sterile capped test tubes • E.coli B • Sterile dilution fluid

  8. Procedure • Four 1 liter beakers were filled with 500 ml of tap water. The temperatures were adjusted to 5, 10, 30 and 50 degrees C and maintained at these temperatures for the duration of the experiment. • E.coli was grown overnight in sterile LB media. • A sample of the overnight culture was added to fresh media in a sterile sidearm flask. • The cultures were placed in a shaking water bath (37 degrees C) until a density of 50 Klett spectrophotometer units was reached. This represents a cell density of approximately 109 cells/ml. • The culture was diluted in sterile dilution fluid to a concentration of approximately 103 cells/ml. • The solution was mixed by vortexing and allowed to sit at each selected temperature (0, 5,10,30,50° C) for 15 and 30 minutes. • At the end of each time period the solutions were vortexed, and .1 ml aliquots were removed from the tubes and spread on LB agar plates. • The plates were incubated at 37° C for 24 hours. • The resulting colonies were counted. Each colony is assumed to have arisen from one cell.

  9. Conclusion • The evidence (p<.05) strongly supports the alternative hypothesis. The null hypothesis is rejected. All tested temperatures appeared to significantly reduce E.coli survivorship. • The second hypothesis that increased exposure time to a given temperature would adversely affect survivorship is also strongly supported.

  10. Limitations • -20° C Freezing Temperature is hard to maintain throughout vortexing and pippetting • Number of trials

  11. Extensions • Wider range of temperatures • Longer exposure times • More Trials

  12. Sources • United States Department of Agriculture (USDA) • Centers for Disease Control and Prevention (CDC) • Food and Drug Administration (FDA) • World Health Organization (WHO)

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