Mold

*Many* thanks to Ala Rekrut for shedding light on questions about
the health hazards of non-viable mold spores (that is, spores or
conidia that have lost the capacity to generate active mold growth).
Although most writers clearly distinguish between active mold and
dormant spores, none of the literature I've read (including
Florian's excellent, highly readable paper and Brezner's LJ article
on microwaving for insect extermination) is authoritative on *this*
question.  Most writers indicate that spores are extremely difficult
to eradicate (that is, to render non-viable).  My questions have to
do with the residual allergenicity or toxicity of non-viable spores.
Ala's comments seem to indicate that even "killed" spores remain
hazardous to people--can you provide me with a citation, or is this
a common sense precaution based on the absence of evidence to the
contrary?

I've been e-corresponding with a microbiologist named Phil Geis on
this subject.  He's provided a number of citations on microwaving
and microbiological species.  Summaries of what I found most
pertinent are attached.  I'll be glad to forward the whole list with
full abstracts to anyone who asks.  He asked if I thought a review
of this literature would be helpful--I said I did.  Any other
opinions?

    Chen, S.Y; Dickson, D.R; Mitchell, D.J.
    "Effects of soil treatments of the survival of soil micro-
    organisms". Journal of Nematology 27(4 SUPPL.): 661-663
    Abstract:  Improved methods are needed for reducing or
    eliminating specific soil inhabiting microorganisms (e.g.
    nematodes). Microwave heating of soil decreases soilborne fungi
    and bacteria, but not Pasteuria spp. Bacterial and fungal
    colony-forming units were reduced to nondetectable levels in
    microwaved heated field soil (650 watts) at 5.2% moisture when
    treated for 6 minutes and 4 minutes, respectively.

    Stephenson, M.M.P; Kushalappa, A.C; Raghavan, G,S,V.
    "Effect of selected combinations of microwave treatment factors
    on inactivation of Ustilago nuda from barley seed". Seed Science
    and Technology 24(3): 557-570
    Abstract: The effects of combinations of absorbed microwave
    power (AMP) and pulsing (PUL) on barley seeds highly infected
    (68.9%) with the loose smut pathogen Ustilago nuda (Jens.)
    Rostr. were investigated. ...moisture content of the seeds was
    fixed at 21% on a dry weight basis and the microwave treatment
    duration at 75 min. Barley seed germination and seedling vigour,
    the latter measured as the mean plumule length (MPL), were not
    significantly affected by most of the microwave treatments
    compared to a non-treated control, except at high levels of AMP
    and PUL. The percentage of seed germination was highly
    correlated with the MPL (r = 0.86)....The effectiveness of
    microwave treatments to inactivate U. nuda was evaluated based
    on seedling infection (SI) at the second true leaf stage and
    plant infection or smutted plants at maturity (PI). There was a
    poor correlation between %SI and %PI (r = 0.46)....SI and PI
    were reduced to 26.7 and 11.6%, respectively, for the best
    microwave treatments, as compared to 50.1 and 45.3%, for the
    untreated control. Therefore, up to 74.3% reduction of the
    effective inoculum was achieved by using 0.5 W/g AMP and 50/10 s
    of PUL. At 0.5 W/g AMP, when PUL was reduced to 40/20 s, the
    effective inoculum was reduced by more than 56.0% without
    significantly affecting seed germination and vigour.

    Rosaspina, S; Salvatorelli, G; Anzanel, D; Bovolenta, R.
    "Effect of microwave radiation on Candida albicans". Microbios
    78(314): 55-59
    Abstract: Microwave exposure (90 s) provides an effective, rapid
    sterilization for surgical scalpel blades which have been
    contaminated with Candida albicans. SEM analysis showed that
    microwave irradiation induced a morphological modification of
    the cells. The longer the exposure time the greater such
    alterations and this micro-organism in effect fractures after 9
    min. No evidence was found of morphological alteration of the
    fungus after being submerged in boiling water for the same
    amount of time even though cell death was actually achieved.

    Schading, R.L; Carruthers, R.I; Mullin-Schading, B.A
    "Rapid determination of conidial viability for entomopathogenic
    hyphomycetes using fluorescence microscopy techniques".
    Biocontrol Science and Technology 5(2): 201-208
    Abstract: The viability of conidia from two species of
    deuteromycetes fungi pathogenic to insects was determined using
    two fluorochrome stains, fluorescein diacetate (FDA) and
    propidium iodide (PI)....FDA fluoresces bright green in viable
    conidia and PI fluoresces red in non-viable conidia,...Conidia
    from two isolates of Paecilomyces fumosoroseus (Wize) Brown and
    Smith and two isolates of Beauveria bassiana (Balsamo) Vuillemin
    were evaluated. Conidia were suspended in deionized water and
    half of each suspension was treated with microwave radiation to
    kill all the conidia. Conidia were tested for viability in
    non-microwaved suspensions in a mixture (ca. 1:1) of viable and
    non-viable conidial suspensions, and in the microwaved
    suspensions that contained all non-viable conidia. No
    significant differences were observed...between germination
    tests...[and] viability tests conducted with [fluorochrome
    stains.] One isolate of B. bassiana that had been damaged in
    storage was also tested. Differences were observed between the
    actual germination and the percentage of viability determined
    using FDA or FDA plus PL[.] Damaged conidia maintained a measure
    of viability and fluoresced green, but did not fully germinate.

Karen Motylewski
Director, Preservation and Conservation Studies
Graduate School of Library and Information Science
SZB 564/D7000, University of Texas at Austin
Austin, TX 78712-1276
512-471-8290
Fax: 512-471-8285

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                  Conservation DistList Instance 11:42
                Distributed: Wednesday, November 5, 1997
                       Message Id: cdl-11-42-003
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