of different compositions. This method has been previously used to osmotically stress bacteria and to dose microcolonies of bacteria and Candida spp. during rapid drug susceptibility testing. Microcolony-based methods combined with fluorogenic dyes and imaging may offer particular advantages with respect to studying filamentous fungi, a group of organisms for which dispersed growth in liquid culture is not necessarily the most relevant. In this study, PAO culture was used to explore the lethality of caspofungin and anidulafungin to A. fumigatus, and also the recovery from these drugs, by imaging individual microcolonies and by quantifying the effects. limitation, but this was not relevant to the microcolony studies presented in this work. Growth of A. LGX818 fumigatus and A. terreus with anidulafungin and caspofungin Results Germination and growth of A. fumigatus and A. terreus on PAO Dispersal and germination of conidia on PAO. Conidia purified from clinical isolates and a reference strains of A. fumigatus and A. terreus were inoculated onto 3668 mm strips of PAO placed on Sabouraud agar to a density of from 5 to 50 cfu/mm2. After incubation for 4 to 10 h at 37uC the fungi on PAO strips were stained with Fun-1/calcofluor white and the percentage germination assessed. Both germinated and ungerminated conidia of both species could be imaged and distinguished upon PAO by this method. The distribution of conidia immediately after inoculation was predominantly of single spores. The median swelling and outgrowth times for all strains tested were similar on PAO placed on Sabouraud agar compared to growth directly on the same agar. This suggests conidia can be inoculated to single cfu on PAO and germination occurs with the same efficiency to that seen on agar. Growth of mycelia on PAO. Hyphal extension rates were calculated from transmission light microscopy, and were found to be similar on PAO compared to culture directly on the same agar medium. Scanning electron microscopy suggested that the tips of vegetative mycelia of A. fumigatus were lifted off the surface of the PAO during growth; observation by light microscopy supported this conclusion. Visible colonies of all strains tested were smaller on PAO compared to agar, when observed after 24 and 36 h. The formation of conidiophores on PAO was delayed by 12 to 24 h. Taken together, these data suggest that PAO is suitable for the culture of fungi to microcolonies with no nutrient limitation caused by the interposition of a 40% porous filter between agar and the fungus, the changes in surface properties of the growth surface having a major impact. Macroscopic growth was somewhat restricted, presumably by nutrient Microcolony Analysis of Aspergillus Conidial Swellinga Strain JBZ11 JBZ17 JBZ32 CWZ93 CWZ855 ATCC204305 CWZ59 A. fumigatus A. fumigatus A. fumigatus A. fumigatus A. fumigatus A. fumigatus A. terreus Agar 4.5 h 4h 4.5 h 5h 4.5 h 4h 6h PAO 4h 5h 4.5 h 5h 5h 4.5 h 6h Outgrowtha Agar 6.5 h 6h 7h 7h 6.5 h 7h 8h PAO 7h 6h 7h 6.5 h 
6.5 h 7h 8.5 h Hyphal ” Extension b Agar 24.9+/24 18.0+/22 19.0+/25 22.5+/26 16+/23 20.0+/24 11.0 PAO 19.1+/24 16.1+/23 16.8+/24 20.6+/247 17+/24 16+/23 8.9 a Calculated from the area of.100 conidia or microcolonies per data points; taking measurements every 30 min after inoculation. ANOVA with Tukey post hoc “2436504 test was to determine first time point with a significant increase in area comparing unswollen conidia at T = 0 with subsequent time points to determine swelling tim
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