Efficacy of a selective isolation procedure for members of the Pseudallescheria boydii complex

Members of the P. boydii species complex (Microascaceae) are frequently involved in human opportunistic disease. Studies indicate that the prevalent habitat of P. boydii sensu lato is in agriculturally exploited or otherwise human-impacted soils. Quantitative analysis of fungal indicators in the environment can be exploited for monitoring of general environmental changes, as well as for understanding local population changes and its epidemiological consequences. In this study we present the development and testing of a semi-selective isolation procedure for P. boydii and related species. Three general media, DG18, rose bengal agar and five variations of modified Leonian's agar with and without benomyl were tested. Germination percentages of P. boydii, S. prolificans, Petriella spp. and Aspergillus fumigatus (control) were evaluated. Tests were carried out on the success of P. boydii isolation from inoculum mixed with A. fumigatus. Subsequently the procedure was applied to water, sediment and soil samples. On the newly introduced semi-selective medium (SceSel+), the germination of P. boydii was superior or similar to that seen on the other media tested. P. boydii was isolated from mixed cultures only on SceSel+ but not on SceSel without benomyl. Isolation from environmental sources with SceSel+ was successful, and human impacted soil was confirmed as the predominant habitat of P. boydii.