Chapter 25: Hand washing
Doesn't everyone always tell you to wash your hands? Sure. And for a number
of good reasons. Your hands are the most likely body surface to pick up germs,
and thus serve as one of the most important means of transmission of pathogens.
Viruses, such as those that cause the common cold, and bacteria (e.g. E. coli)
are easily transmitted this way. And yet these microbes are not normally found
living on your hands & fingers. They are considered to be transient microbes.
Your skin secretes fats, oils, and other substances which coat your skin,
especially on your fingertips. These can then trap microorganisms from the
environment. Good hand-washing protocols are designed to remove these fats and
oils, and the accompanying transient microbes which are sometimes associated
with disease. Hand-washing does not, however, get rid of the normal resident
microbiota found on your skin.
A good hand-washing protocol includes using hot water, soap, and vigorous
rubbing (friction) to dislodge microbes and dissolve the oily film that
traps transient microbes. You use hot water and soap for the same reason that
you'd use these to wash greasy dishes!
Recently, many antimicrobial soap products have also come on the market. The
foam & alcohol-based soap now used on the Plattsburgh campus in one example. We
will use this type of soap, as well as standard liquid/solid soap, and compare
their relative effectiveness in doing the job. To evaluate the effectiveness of
hand-washing, we will make "before" and "after" fingerprint impressions on agar
and count the number and variety of microbial colonies that grow after
Materials & Methods
Each student will need 2 TSA plates
- Use the soap dispensers in the bathrooms at the end of the 3rd floor
- Use the Hand sanitizer dispenser on the second floor (outside room 205)
- Important: Do NOT wash your hands at the start of today's lab!
- You will be assigned one of 4 hand washing
- Hot water & traditional soap:
- Cold water & traditional soap:
- Hot water alone:
- Cold water alone:
- Label your TSA plates "before" and "after"
- Place a fingerprint of all 5 fingers onto the agar surface of the 'before'
- Follow the hand-washing protocol assigned to you
- Place a fingerprint of all 5 fingers onto the agar surface of the 'after'
- Bring both plates up front to be incubated
After 24 - 48 hours of incubation
- Count the number of colonies on each agar plate. Add up the colonies from
all 5 fingers. There will likely be a lot of colonies to count! Put a small
dot onto the back of the agar plate as you count a colony - this will help
you not lose track of which colonies you have already counted.
- Next, determine how many different kinds of colonies you have on your agar
plates. Note down the physical characteristics of the colonies in your
notebook. For example, you may note that a colony is white and small.
- Small white round colonies (probably S. epidermidis)
- Small round yellow colonies (S. aureus or Micrococcus)
- Large opaque white colonies (Bacillus)
- Beige 'slimy' medium colonies (probably Gram-negative bacteria)
- Large slimy-looking colonies (Yeasts)
- Record your data on your data sheet and on-line. Copy other students'
data on your data sheet as well
- After all lab sections have uploaded their data, download the class
data. Copy it into an excel spreadsheet. Sort the data by protocol.
Calculate the average for each category. Calculate the average CHANGE in
© 2003 - 2015 Josť de Ondarza, Ph.D.