The Five Second Rule: Fact or Fiction

1
The Five Second Rule Fact or Fiction?

• By Larissa Hurd

2
Problem Statement

• Does time affect the amount of bacteria a food
  particle picks up?

3
Hypothesis

• If the food is left in contact with E.Coli for
  five seconds, then it will have less bacteria
  than food left in contact with E.Coli for ten and
  thirty seconds because the bacteria has more time
  to bond to the food.

4
Variables

• Manipulated- amount of time in seconds
• Responding- how much bacteria is absorbed
• Controlled- no airborne bacteria present during
  lab, type of bacteria (E. Coli), amount of
  bacteria, pressure applied to food, same amount
  of surface area

5
Procedure

• Make 30 LB Agar trays, using sterile technique
• Mix Luria-Bertani antibiotics (Amplicillin 100
  mg/ml, Kanamycin 25 mg/ml, Streptomycin 20 mg/ml,
  Spectinomycin 20 mg/ml) and E. Coli in Steriguard
  III
• Put in incubator shaker overnight
• Take E. Coli solution out and dilute with
  Luria-Bertani and buffered water
• Adjust to uniform density using the
  Spectrophotometer (3 X 106 cells/ml)
• Place crackers and turkey in Steriguard III for
  two minutes under UV light
• Place 3ml diluted E. Coli solution onto bottom of
  plastic container, swab drop out into a into
  quarter-sized circle
• Place cracker on solution for one second
• Lift with tongs and swab one diagonal line across
  cracker
• Swab tray using diagonal zig-zags twice across
• Label tray with food and time
• Clean tray with ethanol and paper towels
• Repeat steps 7-12 using 0 second, 5 second, 10
  second, and 30 second
• Repeat steps 7-13 using turkey (instead of
  cracker)
• Place all trays in oven at 30?C for 24 hours
• Remove trays from oven and count three sections
  of E. Coli on each tray
• Dispose of all trash in bio-hazardous waste bin
  and sterilize work space

6
Data
7
Conclusion

• In looking at my data, I reject my hypothesis
  that if the food is left in contact with E. Coli
  for five seconds, then it will have less bacteria
  than food left in contact with E. Coli for ten
  and thirty seconds because the bacteria has more
  time to bond to the food.
• During my experiment, I learned that after five
  seconds there is not a great difference in how
  much bacteria is picked up by food. At five
  seconds there was an average of 229.67 bacterial
  colonies, at ten seconds, an average of 262.3,
  and at thirty seconds, an average of 236. All
  three of these are in a 33-colony range of each
  other. Basically, this means there is very little
  difference if you drop a piece of food for five
  seconds or thirty seconds. I have also
  discredited the five-second rule since I found
  out there was no difference in the amount of
  bacteria picked up from five seconds to thirty
  seconds. (So essentially, you can call it the
  thirty-second rule.) If you drop a piece of food,
  pick it up as soon as you can, but keep in mind
  there is no difference between leaving it on the
  floor for five seconds or thirty seconds.
• The amount of bacteria absorbed is due also to
  many other factors besides time. So keep in mind
  the environment the food has been dropped in and
  the physical properties of the food. I would like
  to do more testing to see how these factors
  manipulate the bacterial levels. Through my
  experiment, I did not research in depth what
  levels of bacteria cause illness, but if you drop
  food you need to evaluate where you dropped it,
  and how dirty that surface is before worrying
  over how much time has lapsed.