Teaching Under the Microscope
by Christine Dunnington Fenton M.Sc.
Member of the New Zealand
The most favoured practical lesson for
Microbiology must be environmental sampling. You know the one, open
agar plates on the windowsill, swabs taken from all sorts of places
then smeared on a plate. Incubate, and then look at all the pretty
Yes, it allows students to 'see' the unseen - all
the microbe life from supposedly clean surfaces and the fuzzy bits that
we breathe in. But is it good Science and more importantly, is it safe?
Can concentrating unknown microorganisms and exposing the plates for
inspection by inexperienced and curious students be wise?
I personally have known a fourth form boy
ask which colonies should he lick so he can get a day off school! A
horrifying thought. The normal environmental sample could concentrate
pathogens and other nuisance organisms in enormously high numbers. For
instance Serratia marcescens has known carcinogenic properties
and has red to pink colonies - very attractive.
Mucor, Penicillium and Aspergillus
moulds are fascinating and they grow very easily on bread but can
affect people with asthma and allergies. Any of which could be present
on an environmental sample.
"The Guidance Manual for NZ Schools"
(Safety and Biotechnology Education, Ministry of Education), recommends
that you NEVER work with unknown living materials.
Rather than doing the typical environmental
sample you purchase known microorganisms to work with. Bakers' yeast (Saccharomyces
cerevisiae ) and yoghurt bacteria from commercial home yoghurt
packs can be used safely. Another alternative is to use laminated
colour photographs of the cultures grown on petri dishes or a web camera with the display piped through
the computer onto a monitor in the classroom.
However, I feel like the traditional
environmental sample can still be done safely by following these
NEVER sample from body fluids.
This includes swabs taken from the mouth, nose or sneezing and coughing
directly onto plates.
NEVER sample from sinks,
toilets, rubbish bins and taps.
ALWAYS use sterile swabs to take
samples with. Clean or new does NOT mean sterile.
Once you have exposed your petri dish
plates then seal them with "parafilm" or sellotape or even glad wrap so
that the lid cannot be removed.
ALWAYS incubate at room
temperature. Be aware that this is not a "safe" temperature - some
pathogens can grow at temperatures below 37o C - they just
reproduce at a slower rate.
ALWAYS adequately destroy plates
after examination. Do not just thrown in the bin! (yes, this happens).
Either pressure cook the plates at 15 lbs pressure for 15 minutes then
discard or bag the plates up and microwave until the plastic melts,
then discard. Alternatively you can incinerate or soak in 10% bleach
(NOTE: household bleach is only 3% sodium hypo-chlorite) for 3 days.
Anything else is unacceptable and unwise.
Presenting Microbiology to the students in
an interesting way to spark the interest of budding young Geneticists
and Microbiologists is of course very important. But for many the lab
practicals done at High School will be the only time they are exposed
to life under the microscope so let's keep it as safe as possible.
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