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Ascospore:
Ascobolus
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Deuteromycete:
Stemphylium
.
Basidiospore:
Coprinus
.
Deuteromycete:
Cladosporium
.
Ascomycete:
Didymella
.
Basidiomycete:
Agrocybe
.
Deuteromycete:
Periconia
.
Ascomcyete:
Xylaria
.
Deuteromycete:
Alternaria
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INTRODUCTION
- To date
no perfect identification technique has been found for fungal spores.
The two principle methods used are culturing and visual identification
and there are advantages and disadvantages to both these methods. Detailed
information on sampling principles and procedures, instruments, equipment
and counting techniques can be found at the European
Aerobiology Information site.
CULTURING
- Spores
are collected onto petri-dishes containing a nutrient medium. The dishes
are incubated to allow spores to germinate and form colonies, which
can then be identified and counted. This method is limited for five
reasons.
- 1) This
type of study is usually limited by the types of spores which will grow.
Basidiomycetes and ascomycetes cannot be grown on culture media or if
grown develop into alternative anamorphic forms which cannot be identified,
(Lacey, 1996). This method is restricted generally to studies of fungi
imperfecti.
- 2) Differences
in competitive abilities for various genera will influence growth and
Singh et al., (1995) postulates that the growth of Alternaria
is inhibited by the presence of Aspergillus flavus and Aspergillus niger
in particular. Therefore the colonies which are counted may not be representative
of the spores which were present in the air.
- 3) The
culture plates are overloaded very quickly, so that each plate represents
only the spores present for a very brief period, (10 to 30 minutes).
- 4) Only
viable spores can be cultured although there is no evidence to suggest
that there is any difference in the allergic responses, by atopic individuals,
between viable and none viable spores.
- 5) Colonies
may have derived from hyphal fragments rather than spores, (Ebner and
Haselwandter, 1989).
- 6) Culture
results are dependant upon the choice of culture medium and incubation
temperature.
- 7) Sexual
spores present in the air may germinate to produce the asexual (imperfect)
growth form which may not be identified as being the same fungi. For
example, the parasitic fungi Trichophyton which causes skin
diseases in Humans and other animals is the conidial or imperfect (asexual)
anamorph of the Ascomycota fungi Arthroderma.
- The principle
advantage of cultuing is that it can allow the proportions of Aspergillus
and Penicillium to be determined. This is not possible using visual
identification methods.
VISUAL
IDENTIFICATION
- Visual
identification is based upon morphological features such as colour,
size and shape. One of the most frequently used samplers is the Burkard
Volumetric spore trap. Here a drum which is covered with a length of
cellophane tape which is rotated slowly (2 mm/hr) part an inlet orifice.
The tape is coated with a sticky surface. The most frequently used tape
coating is a Vaseline/paraffin mix to provide a sticky surface. Air
is sucked in at a constant rate (10 litres/min.) and the spores are
impacted on to the sticky tape coating. This tape is cut into sections
and mounted on to glass slides for visual identification. Each 48 mm
of tape represents a 24 hr period, so because the drum moves at a known
distance in a specified time, diurnal as well as seasonal variation
can be assessed.
- The principle
advantages of this method over culturing technique include an increased
range of types of spores which can be recorded and the ability to study
diurnal as well as seasonal trends. In addition the spores do not have
to germinate into colonies before they can be identified which allows
airborne concentrations for groups which cannot be cultured, such as
ascomycetes and basidiomycetes, to be recorded. Using volumetric sampling,
together with visual identification, in contrast to culture methods,
has demonstrated the high numbers of ascospores and basidiospores present
in the air.
- The major
disadvantages with visual identification are:
- 1) Many
spores are morphologically similar and cannot be identified to genus
level. Examples include many basidiospores which Kendrick (1990) states
are often impossible to identify with any degree of certainty. Morphological
similarities are used to produce groups of spores such as Aspergillus
and Penicillium, which form the Aspergillus/Penicillium
group.
- 2) In
addition to morphological similarities many spores, particularly ascomycetes
and basidiomycetes, are small and hyaline (colourless) and can be extremely
difficult to see. Therefore the concentrations recorded for these types
may be an under estimation of the actual numbers present.
- 3) The
trapping efficiency of volumetric samplers reduces once the spore diameter
falls below 5 micrometres, (D'Amato and Spieksma, 1995). Therefore these
spores will be underestimated when the resultant tape is examined.
- For studies
where accurate estimations of most airborne spore concentrations are
required the visual identification method is preferable. However, the
ideal method would involve both culturing and visual identification
surveys symaltaniously. This would allow groups such as Penicillium/Aspergillus
to be divided and their proportions to be assessed individually.
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SITE INDEX
Home
Introduction
Fungi Imperfecti/Deuteromycota
Ascomycota
Basidiomycota
Fungal Spores and Allergy
Assessing the Effects
Sampling Spores
Culturing
Visual Identification
Details and Images of some common spore types
References
Links
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