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cleaning up slime

Leon Avery leon at EATWORMS.SWMED.EDU
Sat Jan 14 09:50:48 EST 1995

> We are having problems with various types of "slime" on our worm
> plates, which we believe is bacterial contamination.  It causes the
> worms to burrow, making scoring and crosses difficult to impossible.
> Does anyone know of any solution to this problem?  We have tried the
> bleach/NaOH treatment recommended in the worm book, with marginal
> success.  It helps, but the worms come back.  We have also tried
> plates with 200 microgram/ml streptomycin with no luck.  Has anyone
> tried other antibiotics against these creatures?  Does anyone know
> of any other solution to this problem?

In my experience, bleach treatment is absolutely effective at getting
rid of bacterial or fungal contaminants.  I do it as follows: mix 2.5
ml commercial bleach, 2.3 ml water, and 0.2 ml 50% NaOH.  Use within a
few weeks.  (The worms should dissolve; if they don't your solution or
your bleach is too old.)  Put a drop in the center of a fresh seeded
plate.  Pick 5-10 gravid adult hermaphrodites into the drop.  Next
day, pick some of the L1s that have hatched to a new plate.  I've
heard that one occasionally gets a few contaminants surviving on the
first bleach plate--that's the reason for picking to a new plate on
the second day.  In practice, this has never happened to me.

We include 200 ug/ml streptomycin and 10 ug/ml nystatin in our plates.
Most worm people don't do this; they say all their contaminants
rapidly become Str-R, and then it's just as bad as before.  I think
these people are expecting too much: if you put some effort into
keeping your plates clean, strep will make that effort more effective,
but it won't eliminate the problem all by itself.  Most bacteria that
drop in from the air are Str-S.  Occasionally you'll get a Str-R
contaminant, and then you have to clean it up by repeated transfers or
bleach.  The nystatin does a good job on yeast contaminants, I think
(at least I used to see lots of these before I used it, and none
after), but is almost completely useless on molds.  They're our main
problem.  We deal with it mostly by discarding (gently) or parafilming
plates that become moldy, so the spores don't get released into the

It really is possible to keep worms relatively free of contamination.
Keep trying.

If you're using the NGM recipe in the worm book, I would recommend
increasing the agar from 1.7% to 2% or 2.2%.  This doesn't prevent all
burrowing, but it enormously reduces the problem.

Leon Avery					   (214) 648-2420 (office)
Department of Biochemistry			            -2768 (lab)
University of Texas Southwestern Medical Center             -8856 (fax)
5323 Harry Hines Blvd				   leon at eatworms.swmed.edu
Dallas, TX  75235-9038			  http://eatworms.swmed.edu/~leon/

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