Introduction to Fungi, Third Edition

260 ARCHIASCOMYCETES
There are many oddities about Pneumocystis
(Stringer, 1996, 2002). One is that this fungus
lacks ergosterol, utilizing cholesterol instead
as its major membrane sterol. This explains
the insensitivity of Pneumocystis to amphotericin
B, the most important drug against fungal
infections of humans (see Fig. 10.9). In contrast,
although the cell wall of trophic cells of
Pneumocystis is unusually thin, this fungus is susceptible
to inhibitors of b-(1,3)-glucan synthesis
such as echinocandins (Schmatz et al., 1990).
Thirdly, there are only two rRNA gene repeat
units, in contrast to other fungi which contain
some 50 250 copies of it (see Fig. 1.24).