Relationship between proteolytic activity of Aspergillus fumigatus and the fungus' invasiveness of mouse brain

Abstract

This experiment was carried out to determine whether proteolytic activity of Aspergillus fumigatus was enhanced in the mouse brain during advance in growth of hypae, and if any relationship might be demonstrated between the proteolytic activity of the fungus and its invasive ability for the mouse brain.

The K-2 strain of A. fumigatus and male mice of ddy line weighing 22±1 g were used in this experiment. Each mouse was inoculated intravenously with 5×10⁶ conidia of the strain suspended in 0.2 ml. phosphate buffer solution supplemented with 0.01 per cent Tween 80. Mice were sacrified at 4 hours' intervals up to 40 hours after inoculation and at an hour's intervals later. Two mice were assigned for each time. Each brain obtained was fixed in 10 per cent formalin and was cut into three sections from which histopathological specimens were prepared.

The brains over 40 hours after inoculation were markedly swollen and abundant hypae were observed in the specimens. The extent of the fungal growth in the specimens from the mouse brain was 1.60, 7.71 and 10.84 per cent at 32,45 and 49 hours after inoculation, respectively.

For assay of the proteolytic activity in the mouse brain, three groups of fifteen mice each were tested with the K-2 strain. These groups of mice were inoculated with 5×10⁶conidia of the strain and sacrificed 0,32 and 45 hours after inoculation, respectively. Then the brains pooled in each group and four volumes of phosphate buffer solution was added. The material was homogenized and used as test samples (enzyme solution). The proteolytic activity was measured quantitatively by a modification of Anson's method.

The proteolytic activity in the mouse brain sacrificed 0,32 and 45 hours after inoculation was 0.00, 0.08 and 0.13, respectively, as expressed by the optical density.

In conclusion, it was possible to confirm that proteolytic activity increased in the mouse brain in proportion to the growth of hyphae in it.