Most
embryologists have encountered the presence of mold in media or even cultures.
There are a number of routes of contamination each of which, offers a control
point. Mold and yeasts, are eukaryotic heterotrophs which, absorb
nutrients though a cell wall and membrane. Molds typically germinate with
branching hyphae developing into mycelium and reproduce both asexually and
sexually by spore formation. Yeast is the unicellular variety and reproduces
largely by budding.
Mold
and yeast are usually spread by airborne suspension of spores or cells, either
from poor aseptic technique or diffusion. The ability of mold to exist in
laboratories is limited by the level of relative humidity in the laboratory.
Relative humidity is the measure of water in the air compared to its saturation
value at a particular temperature. The American Society of Heating Refrigeration
and Air-conditioning Engineers (ASHRAE) typically call for a relative humidity
in occupied spaces of 30-60%. Keeping the relative humidity between these levels
will reduce mold growth and impair spore viability.
Summer
time in North America is when a lab is most likely to have high relative
humidity. Often times, in extremely hot, moist weather, laboratory air
conditioning may not be able to keep the relative humidity level below 60%.
In such cases, it may be advisable to allow the temperature of the lab to rise
by 3-7 degrees resulting in a decrease in relative humidity. In the case
of winter, the level of relative humidity may drop below the 30% minimum.
This will strongly inhibit mold and yeast survivability but may cause drying of
the eyes and nasal mucosa. It may also have an adverse affect on open culture
systems. A humidification system should be able to correct this by
injecting purified steam or boiling water in the supply air stream, but such
systems need tight control and maintenance.
The
source of mold can be as simple as a fouled air handling system with a failed
HEPA filter. Past instances have also included contaminated mineral oil.
The use of laminar benches has also reduced the possibilities of contamination.
The laboratory staff is a significant source of mold and yeast contamination.
Scrubs, hair coverings, booties are common attire in the laboratories but often
times they are worn casually outside the laboratory and then used in the
laboratory. Hair in particular can present a suitable culture site for
mold. Molds and yeasts find the dead cells and other bio effluvia an
ideal nutrient.
With
an effective HEPA filtration system, sound lab technique mold should be fully
controlled. The water pan of the incubator can be its own problem.
Many laboratory staffers have seen white filaments in the water pans. Frequent
changes and disinfection of the pans is required to control this “water
fungus”. Commonly these include the geneses of aspergillus and
penicillium. . Some laboratories have added low concentrations of copper
salts to the pan in an effort to inhibit mold growth.
Confirmation
of the presence of air borne mold can be done by sampling with Air-o-Cell
cassettes followed by microscopic examination. Spore morphology can provide an
indication of genus and enumeration of total spores per cubic meter of air can
be calculated. Sampling with an Andersen sampler with malt extract agar
(MEA) plates followed by incubation will provide data on the number of colony
forming units, i.e. viable spores. Alternative air sampling can use a
Reuter Centrifugal Sampler. Wipe samples using agar blocks can be used to check
laboratory surfaces for mold. Investigation of environmental systems and
personal laboratory practices should be perused to confirm the source of the
mold. And after all is said and done, yeast colonization may actually not
inhibit IVF outcome depending on the yeast species and restriction of the
growth, but continuing teratogenic effects are unknown.
Please
note that Galileo Research Laboratories, its staff, or any of its associated
members are in no way responsible for or necessarily agree with the opinions
presented here.
