Introduction to Fungi, Third Edition

306 PLECTOMYCETES
Patulin
Although patulin is a small (tetraketide-derived)
molecule (Fig. 11.14e), its biosynthesis is complex,
involving the formation and subsequent
cleavage of an aromatic ring (Moss, 1994). Patulin
is produced by several species of Aspergillus and
Penicillium as well as Byssochlamys nivea (see p. 307),
but the most important producer by far is
P. expansum, a cause of brown rot of apples.
Patulin is often detected in apple juices, sometimes
at concentrations greatly exceeding safety
limits set at or below 50 mgl 1 . It is, however,
destroyed during alcoholic fermentation to wine
or cider (Moss & Long, 2002), or by adding
sulphite. It is also formed by A. clavatus in spent
barley from beer brewing which is often fed to
cattle. Patulin may be carcinogenic; it also reacts
with the sulphydryl groups of proteins, thereby
inactivating enzymes (Mahfoud et al., 2002).
A review of safety issues and methods for analysis
and control of patulin levels in food has been
written by Moake et al. (2005).
11.4.5 Pathogenic species
In principle, all species of Aspergillus and Penicillium
and indeed many other types of fungi can
cause health hazards because of the potential of
their spores to act as allergens to those suffering
from hay fever or asthma. Further, many species
of Aspergillus and Penicillium produce mycotoxins
(see above). In the present section we will consider
only those species which cause mycoses, i.e.
infections which require chemotherapy. Good
general reviews have been written by Kwon-
Chung and Bennett (1992) and Summerbell
(2003).
Aspergillus
Two species cause most of the mycotic infections
associated with Aspergillus. These are A. fumigatus
(69% of all reports) and A. flavus (17% of reports)
(Summerbell, 2003). Both produce similar
diseases. Like many other fungal pathogens of
humans, these species primarily cause infections
of the respiratory tract and the lung, although
wound infection can also occur occasionally. In
immunocompetent patients, non-spreading
‘fungus balls’ (aspergillomas) may be formed
in the lung in cavities caused, for example, by
previous tuberculosis. In immunocompromised
patients, invasive aspergillosis may arise, i.e. the
infection spreads throughout the lung and even
to other organs. Aspergillosis is a major cause of
death among cancer patients and is strongly on
the increase among AIDS sufferers. One reason
why A. fumigatus is a more frequent cause of
infection than A. flavus may be that its conidia
are smaller (3 mm diameter or less) and can
penetrate more deeply into the lung. They are
also more buoyant in the air, and Chazalet et al.
(1998) have routinely measured concentrations
above 1 conidium m 3 air even in protected
hospital environments. This means that every
human normally inhales several hundred
conidia of A. fumigatus every day. One disease
caused almost solely by A. fumigatus is allergic
bronchopulmonary aspergillosis, in which infections
occur in patients already suffering from
chronic irritation of the lung, e.g. due to asthma
or cystic fibrosis. The disease can lead to fatal
destruction of the lung tissue. Treatment by
chemotherapy is possible, with amphotericin B
and the triazole itraconazole being the major
current drugs. In-depth reviews on all aspects of
diseases caused by A. fumigatus have been written
by Latgé (1999, 2001).
Aspergillus fumigatus is a particularly thermotolerant
species with an upper growth limit at
52°C (Dix & Webster, 1995), although it can survive
80°C for up to 60 min (Jesenská et al., 1993).
It is one of the most abundant moulds found in
compost heaps and other situations in which the
decay of vegetation generates heat. Workers at
compost sites are therefore subjected to a massive
spore inoculum, although the incidence of aspergillosis
does not seem to be generally higher
among them. This indicates the opportunistic
nature of aspergillosis in man. In fact, the spores
of thermophilic actinomycetes seem to cause
most of the problems associated with ‘compost
worker’s lung’ (van den Bogart et al., 1993).
Penicillium
In general, species of Penicillium are not as
thermotolerant as Aspergillus, with only relatively
few species capable of growing at 37°C. Consequently,
clinical reports of Penicillium infections