Geographic Distribution of “+” and “−” Isolates of Blastomyces (Ajellomyces) Dermatitidis in North America1

Two hundred and six isolates received from the states and provinces in North America generally recognized as being endemic for Blastomyces dermatitidis were paired individually with each of 3 “+” and 3 “−” tester strains of Ajellomyces dermatitidis. One hundred and twentynine of the isolates were found to be sexually fertile. The failure of 77 cultures to initiate ascospore production was explained by the fact that 44 were known to be more than a year old. Depending on storage conditions, however, some old cultures (notably, one stored at −20 F in 1949) had retained their sexual potency. No evidence was found that more than one species of B. dermatitidis was present in North America. Sterility was considered to be caused by the previously discovered tendency of this fungus to become sterile during repeated propagation by mycelial transfers. This concept was supported by the observation that almost all primary isolates were fertile when paired with strains B784, B788 or their descendants. That isolates from widely scattered geographic areas paired with each other also supported this idea of one species. Evidence for ascospore infection was considered to be tenable but not proved. The apparent distribution of both “+” and “−” isolates throughout the endemic region with few, if any, pockets of all “−” or all “+” infections was considered to be compatible with the idea that ascospores were operative in infection. However, it was considered advisable to wait until studies can be made of this distribution of “+” and “−” infections at the intra-state level before deciding whether or not the “+” and “−” infections are intermingled. Male and female patients were equally infected by both “+” and “−” strains of the fungus. All the “+” isolates were found to have some pigment in the mycelium while the “−” cultures were more often than not white. Attempts to produce a white “+” strain failed. No evidence was obtained which showed that the strains with pigmented mycelium were more infectious as a group than white ones.