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infection in medium

Chris Jones jonesc at phage.cshl.org
Mon Oct 31 15:33:38 EST 1994

In article <199410281220.FAA20722 at net.bio.net>
A910741%JPNTMU00.BITNET at PUCC.PRINCETON.EDU ("Y. Fuyama") writes:

> At 12:08 AM 10/27/94 -0700, gendjc at luxor.latrobe.edu.au wrote:
> >Can anyone help? We've been getting more and more infections of our
> >fly medium. I don't know if they're two different types or not. One sees
> >the medium turn yellower-pale orange with a mucoid surface that flies
> >get stuck in. Another type seems to be where the medium gradually
> >turns from yellow-orange-amber-deep orangy brown. Tis is not associated
> >with the slimeys in fact the medium seems to dry out a bit. Anyway, it's
> >giving us hell and I think incidence is increasing. Our medium uses
> >agar, raw sugar, and yeast. In addition, one of us studies an infection in
> >thflies which is killed by tetracycline so he must avoid using that in
> >the medium.
> >Any ideas?

In the past we've had a lot of trouble with bacterial infestations of
the medium, usually of the milky-white-slime ilk, but who's to say what
kinds of bugs like your food? Anyway, we now routinely apply one of 4
combinations of  antibiotics to every batch of food, rotating them to
avoid encouraging resistance by the bacteria.

1) Ampicillin + chloramphenicol (each at 50 ug/ml final) Stock
solutions = each @ 1000x, Amp in water, CAM in EtOH. Mix just before
using to avoid precipitation of the CAM.

2) Gentamycin + Doxycycline (each at 50 ug/ml final) Stock = each @
1000x in water, can make as a mixed stock.

3)Amoxicillin + Cefamandole (100 ug/ml and 150 ug/ml respectively)
Stock = each @ 1000x in water, can make as a mixed stock. (pH may need
to be raised slightly for complete suspension.)

4) Hexamethylene tetramine, mandelate salt (= methenamine mandelate)
 (4 mg/ml) Stock = 400 mg/ml (Yes, that's 0.4 g/ml!)

Store stock solutions in aliquots at -20oC.

DO NOT add antibiotics to hot food, as this will seriously affect their
potency.  Add as a dilution from stock to the surface once the food has
solidified to give the final concentrations shown. For convenience, we
dilute the stocks so that we add 70 ul of solution to vials and 500 ul
of solution to bottles -- note that this enables you to make a single
dilution (assuming your bottles contain about 7 times as much food as
the vials) -- and dry the food as long as needed.

The latter two combinations are bacteriocidal against all four
candidate contaminant cultures we've tested.  Fly viability appears
unaffected by any of them.

Hope this helps. (And if the original poster could contact me, there's
a vacationing colleague who would be interested in any info you might
have on tetracycline effects in Drosophila; thanks).

Chris Jones (jonesc at cshl.org)
Disclaimer: yeah, yeah, yeah...

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