Comparison of virulence between clinical and environmental isolates of Aspergillus fumigatus.

Using a mixed infection model of murine invasive pulmonary aspergillosis, the comparative virulence of three clinical and four environmental isolates of Aspergillus fumigatus was investigated after intranasal inoculation. Coloured conidiospore mutants were first derived from clinical strains by ultraviolet mutagenesis and then compared with the parental strains and environmental strains. When the slight reductions in virulence associated with the spore colour mutations were taken into account, some environmental strains were shown to be less virulent than their corresponding clinical strains. It has yet to be determined whether these differences can account for the observation that many patients with invasive pulmonary aspergillosis appear to be infected with a single strain of Aspergillus fumigatus.