The sterility of trypticase soy broth (TSB) that was frozen
and thawed in disposable plastic syringes and infused via syringe
pump was studied to determine whether ambient air or personnel-transferred
contaminants compromised the sterility of the solution. Samples
of TSB (10, 20, 30 mL) were prepared aseptically in syringes of
three different brands--150 samples for each volume (50 for each
manufacturer). The syringes were placed in zip-lock bags, stored
for 24 hours at -15 to -20 degrees C, and thawed for three hours.
Both positive and negative controls were used. For the test samples,
infusion sets were connected to the syringes under aseptic conditions,
and the solution was infused via syringe pump in ambient air into
polyvinyl chloride minibags before incubation. The remaining samples
were prepared in the same manner as the test solutions except that
they were intentionally challenged with Bacillus subtilis introduced
distal to the plunger. All samples were inspected visually for turbidity
after a 14-day incubation period. There was no growth in any of
the test infusion samples or in samples that were intentionally
contaminated. The negative controls showed no growth; all of the
positive controls showed growth. The sterility of solutions frozen
in disposable plastic syringes does not appear to be compromised
by touch contamination of the plunger shaft or by airborne microorganisms
settling on the infusion system.
Exponential gradient maker using a disposable syringe.
Department of Molecular, Cellular and Developmental Biology, University
of Colorado 80309-0347.
With a simple modification, any disposable syringe can become a
reliable and easy to use exponential gradient maker. The modification
consists of two notches, made with a razor blade, in the borders
of the rubber sealing tip of the plunger. A clamp in the tube connected
to the syringe allows control over solution flow. With the clamp
prohibiting drainage, the body of the syringe is filled with the
desired volume of starting solution I. A magnetic stir bar, small
enough to spin inside the syringe is included. The notched plunger
is introduced until no air space remains. This forms the fixed volume,
closed mixing chamber, while the rest of the volume of the syringe
forms the open chamber. The two chambers are connected through the
notches in the plunger. The ending solution II is poured after the
introduction of the plunger. Opening the clamp allows solution I
in the closed chamber to flow out, and the solution II in the open
chamber flows through the notches and mixes with solution I. This
exponential gradient maker can be reused many times, but the low
cost of the components makes it potentially disposable. This feature
is especially useful when using toxic chemicals, or when pouring
polyacrylamide gradient gels, since the apparatus may be disposed
of after contamination or eventual polymerization.
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