Re: Dust Mites, The Scourge of the Laboratory

["Dr. RONALD de FOSSARD" <rfossard@AUSTARNET.COM.AU>]

I first met mites nearly 25 years ago when they very nearly closed down
one of Australia's first commercial laboratories.  Mould contamination
was everywhere and the owners were throwing out hundreds of culture
vessels every day.  At that time, we just didn't believe that mites
could gain entry to our cultures.  Mite specialists at the New South
Wales Department of Agriculture were called in and confirmed the
presence of mites.

Two points:-
(1)  Mites are very difficult to see.  I had to use x40 magnification
with a stereomicroscope to see them AND it helps to make them move - try
warming the culture vessels.
(2)  Our mite specialists told us that once you've got them they'll
always be around in their experience.

AND YES remove all contaminated cultures  from the incubation areas.

Among the prophylactic measures we take against contamination,
HEPA-filters are operated 24/7 and all cultures are 'bagged'.  Our
standard nursery seed trays can 20 x 250mL culture vessels and we place
this tray of cultures in a plastic bag and simply fold the opening under
the tray - we do not heat seal it.  The idea of the plastic bag is, of
course, to isolate contamination should it occur.

Apart from mopping floors, our main additional treatment is to 'bomb'
the rooms once a week with a Mortein flea bomb (a.i. permethrin and
fenoxycarb).

Mites certainly do not like bleach - in the past, we have added 1%(w/v)
'available chlorine' to contaminated cultures rather than carry
contaminated cultures through the rest of the lab.

I think it's a good idea to assume mite contamination when widespread
mould contamination is encountered and to act on this basis.  BUT quite
recently, I found two bottles (one in each of two plastic bag wrapped
tray of cultures) with mould tracks, tracks which I have always assumed
to indicate mites on walk-about.  This time curiosity got the better of
common sense and, instead of opening the bags to remove the contaminated
botles, I left them untouched testing the idea that the mites would
easily get out of the contaminated bottles and contaminate the other 19
bottles in each tray.  Contamination did NOT occur!