Re: Dust Mites, The Scourge of the Laboratory

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

Frank, I'm assuming that you are referring to the last part of my
contribution, that is to 'mould tracks' NOT being followed by
contamination in some or all of the bottles in the same plastic bags

Up until now, I've simply regarded it as an oddity and tucked it away as
potential trivia.  It really is difficult to explain without coming
around to a conclusion that the tracks must have been caused by mites
and, for some reason, these mites have died in situ or become extremely
lazy.

Occasionally, we get way behind with subculturing and varieties not in
great demand ( in fact, not in demand) get left behind and are only
subbed when they are on their last legs, so to speak.  Under these
circumstances, these old cultures have often grown vigorously and are
a.a. (apparently aseptic) but are either harbouring fungal spores or
have spores inhibited by old culture medium.  Whatever, on subbing,
massive losses of cultures occur due to major mould contamination - BUT
the pattern of contamination never, in my experience, resembles 'mould
tracks'.  'Mould tracks' mean mites (or may be thrips) YES?!

If my 'mould tracks' are caused by mites, the question is why haven't
they spread to other bottles in the tray covered with a plastic bag?  We
use screw-on lids to our glass and/or polycarbonate vessels BUT these
are not tightly screwed-on (we prefer to 'harden' cultures off to some
extent in their culture vessels).

Presently, I'm keeping an eye on two lots of Spathiphyllum cultures,
each variety involving 11 culture vessels and in two plastic bags.  Both
varieties were way overdue for subculture (9 months old), both were a.a
, both were treated with 1%(w/v) 'available chlorine' for 1 to 4 hours
and only the tips of the plants were used for subbing.  One out of 11
cultures showed mould contamination after about four weeks incubation -
that was four weeks ago (that is, the cultures are now 8 weeks old).  I
have not removed the mouldy culture bottles intent now to map the spread
(if any) to the other vessels.  Now, this is an example where there are
no 'mould tracks'.  My conclusion is that, if there are any mites in
either one of the two plastic bags, please stand up and be counted!

I welcome input from members particularly if they amount to something testable.

----- Original Message -----
From: "Frank Sadow" <lab@TARAVALLEY.COM>
To: <PLANT-TC@LISTS.UMN.EDU>
Sent: Tuesday, October 18, 2005 6:22 AM
Subject: Re:  Dust Mites, The Scourge of the Laboratory

> thanks RON-and your conclusion,assumption,recommendation  is??
>
> Dr. RONALD de FOSSARD wrote:
>
> >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!