PATHOGENIC MOLDS
DISEASE CAUSING MOLD
Pathogenic molds usually
produce some type of
infection. The word
pathogenic literally
means, "capable of
causing disease". A
normal, healthy
individual can probably
resist infection by
these organisms
regardless of dose,
however, pathogenic
molds can cause serious
health effects in
persons with suppressed,
underdeveloped, or
compromised immune
systems. In some cases,
high exposure may cause
hypersensitivity
pneumonitis (an acute
response to exposure to
an organism). People
with compromised immune
systems would be,
infants and small
children whose immune
systems are not fully
developed, elderly
people whose immune
systems are essentially
worn out, and anyone
exposed to AIDS,
chemotherapy, pneumonia,
bronchitis, and other
respiratory infections.
Bipolaris Species
The U.S. Government's
Occupational Safety and
Health Administration [OSHA]
lists the following as
the health effects of
Bipolaris mold:
Allergen, Irritant,
Hypersensitivity
pneumonitis, Dermatitis.
Bipolaris australiensis
showing sympodial
development of pale
brown, fusiform to
ellipsoidal,
pseudoseptate,
poroconidia on a
geniculate or zig-zag
rachis.
Colonies are moderately
fast growing, effuse,
grey to blackish brown,
suede-like to floccose
with a black reverse.
Microscopic morphology
shows sympodial
development of pale
brown pigmented,
pseudoseptate conidia on
a geniculate or zig-zag
rachis. Conidia are
produced through pores
in the conidiophore wall
(poroconidia) and are
straight, fusiform to
ellipsoidal, rounded at
both ends, smooth to
finely roughened and
germinating only from
the ends (bipolar).
Description and Natural
Habitats
Bipolaris is a
dematiaceous,
filamentous fungus. It
is cosmopolitan in
nature and is isolated
from plant debris and
soil. The pathogenic
species have known
teleomorphic states in
the genus Cochliobolus
and produce ascospores.
Species
The genus Bipolaris
contains several
species. Among these,
three well-known
pathogenic species are
Bipolaris spicifera,
Bipolaris australiensis,
and Bipolaris
hawaiiensis. The genus
Bipolaris contains about
45 species which are
mostly subtropical and
tropical plant
parasites. However,
several species notably
B. australiensis, B.
hawaiiensis and B.
spicifera, are well
documented human
pathogens. Clinical
manifestations include
mycotic keratitis,
subcutaneous
phaeohyphomycosis,
sinusitis, peritonitis
in patients on
continuous ambulatory
peritoneal dialysis (CAPD),
and cerebral and
disseminated infections.
Pathogenicity and
Clinical Significance
Bipolaris is one of the
causative agents of
phaeohyphomycosis. The
clinical spectrum is
diverse, including
allergic and chronic
invasive sinusitis,
keratitis,
endophthalmitis,
endocarditis,
endarteritis,
osteomyelitis,
meningoencephalitis,
peritonitis, otitis
media (in agricultural
field workers),and
fungemia as well as
cutaneous and pulmonary
infections and allergic
bronchopulmonary
disease. Bipolaris can
infect both
immunocompetent and
immunocompromised host.
As well as being
isolated as saprophytes
on plants, Bipolaris may
be pathogenic to certain
plant species,
particularly to
Graminiae and also to
animals, such as the
dog. It may cause nasal
mycotic granuloma in the
cattle. Bipolaris may
also be isolated as a
laboratory contaminant.
Macroscopic Features
Bipolaris colonies grow
rapidly, reaching a
diameter of 3 to 9 cm
following incubation at
25°C for 7 days on
potato dextrose agar.
The colony becomes
mature within 5 days.
The texture is velvety
to woolly. The surface
of the colony is
initially white to
grayish brown and
becomes olive green to
black with a raised
grayish periphery as it
matures. The reverse is
also darkly pigmented
and olive to black in
color.
Microscopic Features
The hyphae are septate
and brown. Conidiophores
(4.5-6 µm wide) are
brown, simple or
branched, geniculate and
sympodial, bending at
the points where each
conidium arises from.
This property leads to
the zigzag appearance of
the conidiophore. The
conidia, which are also
called poroconidia, are
3- to 6-celled, fusoid
to cylindrical in shape,
light to dark brown in
color and have sympodial
geniculate growth
pattern. The
poroconidium (30-35 µm x
11-13.5 µm) is
distoseptate and has a
scarcely protuberant,
darkly pigmented hilum.
This basal scar
indicates the point of
attachment to the
conidiophore. From the
terminal cell of the
conidium, germ tubes may
develop and elongate in
the direction of
longitudinal axis of the
conidium.
Teleomorph production of
Bipolaris is
heterothallic. The
perithecium is black in
color, and round to
ellipsoidal in shape.
The ascospores are
flagelliform or filiform,
hyaline in nature and
are found in clavate-shaped
or cylindrical asci.
Each ascus contains
eight ascospores.
Laboratory Precautions
No special precautions
other than general
laboratory precautions
are required.
Susceptibility
In vitro susceptibility
testing procedures have
not been standardized
for dematiaceous fungi
yet. Very limited data
are available on
susceptibility of
Bipolaris. These data
suggest that
itraconazole MICs are
variable and
voriconazole MICs are
considerably low.
Amphotericin B and
ketoconazole are used in
treatment of Bipolaris
infections. Surgical
debridement may be
indicated in some cases,
such as sinusitis.
