Virulence Studies of Aspergillus nidulans Mutants Requiring Lysine or p-Aminobenzoic Acid in Invasive Pulmonary Aspergillosis

To identify steps in fungal intermediary metabolism required by Aspergiflus spp. during invasive pulmonary aspergillosis, we have developed murine models involving Aspergillus nidulans as the inoculum. The advantages of using A. nidulans overAspergillusfiumigatus orAspergilusflavus, which are the most common agents of clinical disease, are the well-understood genetics of A. nidulans and a large range of mutants of this species which are affected in a variety of metabolic pathways. Comparison of the virulence of A. nidulans strains carrying mutations which block the biosynthesis of lysine (lysA2)and p-aminobenzoic acid (pabaAIl)shows that lysA2 strains have reduced virulence while pabaAl strains are entirely nonpathogenic. The pathogenicity ofpabaAI strains can be restored by supplementing the drinking water of animals with p-aminobenzoic acid. The results indicate that the availability of lysine in the lung is limited, and p-aminobenzoic acid is probably not available at all. Thus, models of invasive pulmonary aspergillosis involving A. nidulans can be used to identify metabolic pathways that may be essential for the pathogenicity of A. fiumigatus, the predominant pathogenic species, suggesting potential new targets for antifungal therapy.