testing the fist-bump hypothesis

Microbiology 3004
Spring 2013
Fist-bump hypothesis – notes for instructors
Testing the fist-bump hypothesis – notes for instructors
Some potentially pathogenic microorganisms can be transferred from person to person by direct
physical contact. Therefore, reducing direct physical contact should reduce the risk of
spreading disease. Two common greetings are the traditional handshake and the more recent
fist-bump. Because the fist-bump involves less physical contact between two individuals, it
would seem that the fist-bump would transfer fewer microorganisms from one person to another
when compared to the number of microorganisms transferred during a handshake.
Develop a protocol that will test the hypothesis that the fist-bump transfers fewer
microorganisms than a handshake.
Note to instructors:
This lab gives students an opportunity to work in small groups and devise an experimental
protocol to test the fist-bump hypothesis. The instructor needs to steer students away from
impractical protocols - that is protocols that may be excellent ideas but are impractical in the
teaching lab, such as those that require equipment or resources that are unavailable or those
that would require more time or materials than are available. The instructor should work with
the students to identify design flaws in their experimental protocols and to check to see if
positive and negative controls have been included.
The hope is that students will come up with reasonable protocols that can be used to test the
fist-bump hypothesis. However, you should know what has worked well in the past so that you
can steer the students in a direction that is likely to yield usable data. Here is the rough outline
for the approach that has worked best so far:
1. The groups will need sterile water, fresh culture of LAB (or S. marcescens), NA plates,
sterile empty bottles (plastic or glass), sterile glass or plastic beakers, gloves, pipettes,
2. In ~500 ml of sterile water in a plastic beaker prepare a dilute solution of LAB.
3. Two students double-glove their right hands.
4. One student (the donor) dips a gloved hand into the dilute solution of LAB. After
“inoculating” the hand, carefully let excess water drip off the glove back into the
5. The two students then shake hands, firmly for at least 2 seconds.
6. Then the recipient student carefully removes the outer glove and places it in a sterile
bottle with ~25-100 ml of sterile water. The donor keeps their glove on.
7. Repeat the previous steps, but perform with a fist-bump instead of a handshake.
8. An untouched glove should be used as a negative control.
9. Vigorously shake the bottles containing the gloves for 3 minutes.
10. Plate ~100 ul from each bottle onto NA plates. Then plate 90 ul of sterile water onto NA
plates and add 10 ul from the bottles and spread. Dilutions might be necessary
depending on how concentrated the bacteria are more dilutions may be necessary.
11. Take ~4 ml from each bottle and place it into small test tubes for use in the
spectrophotometer. Students should take OD measurements.
12. Take 100 ul from each bottle and transfer it into labeled microcentrifuge tubes. Spin at
12Kxg for 5 minutes. Remove the supernatant. Freeze the pellets. This can be used
for qPCR if times allows.