In the 13 cases (2 in the nail sample and 11 in the strain
sample) where molds such as S. brevicaulis were the only cultures to grow from three serial microscopy-positive specimens,
infection by these fungi is very likely. However, all nine cases
(including three in which dermatophytosis was confirmed) in
which a mold was detected by direct PCR in a case where only
a single patient specimen was available are considered not to
be authoritatively confirmed. Notwithstanding this cautious interpretation, it should be noted that, as calculated above, probably at least 375 Scopulariopsis sp. cells would need to be
present before a positive reaction with the SCOP primers was
engendered. At least four out of our nine cases very likely had
at least this level of viable Scopulariopsis material present.
Thus, though we must refrain from recording these amplifications as fully confirmed cases, the balance of probability suggests that true infection rather than contamination is the most
parsimonious explanation for our positive SCOP primer results. This interpretation also fits well with the relatively small
number of times the environmentally common S. brevicaulis
was detected. Based on the figures given by Gupta et al. (20) in
their Table 3, growth in culture of insignificant Scopulariopsis
sp. inoculum on nails is nearly 2.5 times as common as growth
from a true Scopulariopsis sp. infection, even in an elderly patient population particularly vulnerable to onychomycotic
molds. If small numbers of contaminating Scopulariopsis sp.
conidia were giving rise to positive amplifications, we would
probably have had many more positive SCOP results. Moreover, some of the nononychomycosis-causing molds predicted
by BLAST to react with the SCOP primer, such as members of
the genera Trichoderma, Lecanicillium, and Coniochaeta, are
very common in the indoor environment. If the SCOP primers
were detecting background levels of fungal contamination on
nail material, the proportion of positive results could be very
high indeed.