Home bacterial incubator.

Paul N Hengen pnh at ncifcrf.gov
Thu May 1 12:38:24 EST 1997


David L. Haviland, Ph.D. (dhavilan at IMM2.IMM.UTH.TMC.EDU) wrote:

> I am helping a couple of eleven year olds to do a "science project."  I 
> suggested that they do a study on the efficacy of hand washing and soap 
> manufacturer's claims of being "antibacterial."  I've made some plates 
> and tried a pilot run by touching the agarose then leaving the plates out 
> on the counter.  Some 36 hours later there are one or two colonies.  

| One idea, get a hold of a decent sized box, say 2-3 cubit feet.  Just put a
| 25W lamp in there.  That will warm it up above room temp but heat leakage
| from the box will likely prevent it going much above 35-ish.  It depends on
| how soon you  need to see results and how often the class meets.  The box
| with the lamp may very well yeild colonies within 24 hours.  (I often turn
| on the 60W bulb in my electric oven a hour before I put my bread in there
| to rise - works quite well, so I see no reason why a similar approach
| wouldn't work for growing bacterial colonies.)  I know, this is the methods
| sub, not rec.food.cooking!

We used to do an experiment like this for 1st year students in our micro lab.
We articifically contaminanted one persons gloved hand with a culture of
indicator bacteria, a Seratia marcescens strain so that if grown at RT, the
colonies would appear as red. The students took turns shaking hands, recording
the persons name, then swabbing the hand to plate any bacteria. Of course the
class did not know before hand who was the "Typhoid Mary". Makes for an
interesting STD-epidemiology study and discussion in the class room, and
it's perfect for high school students. You could do the same, but instead of
shaking hands, you could wash your hands each time with a different technique,
from simple wiping to antibacterial soap.

Anyway, about the incubator, I made one from a plastic box and a fish tank
heater with a thermostat placed in a small tub of water within the box. You can
adjust the thermostat for warm water to heat and humidify the box all in one
deal. Also, there are warming devices like a snake rock or heating pad that
will also work. But I have to say that the RT growth of S.m. is kinda fun and
only takes a weekend to do. Plate on friday -> red colonies on monday.

--
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* Paul N. Hengen, Ph.D.                           /--------------------------/*
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