Abstract
The main target organ of Aspergillus fumigatus is the lung, and therefore, and it is natural that many medical mycologists have tried to make animal models of pulmonary aspergillosis. However, A. fumigatus also has a predilection for the brain. Even though the frequency of cerebral aspergillosis is approximately 6%, almost all patients die within a few months. The study of animal models of cerebral aspergillosis is thus very important for prevention and therapy of the disease.
In 1969, the authors isolated a strain of A. fumigatus which has a remarkable predilection for the mouse brain. Their successive studies revealed a few other strains of A. fumigatus also having a predilection for the mouse brain. This property is genetically stable and passed on to the new generation. When the strains possessing this property are inoculated on brain heart infusion agar medium supplemented with skim milk at a rate of 2%, their growth rates slow down and clear melting rings appear around their colonies. There is thus a definite relationship between the invasiveness of the mouse brain by A. fumigatus and its proteolytic activity.
It is important from the standpoint of preventive medicine to understand the percentage of such strains existing in nature. This time, the authors investigated 149 strains of A. fumigatus which consist of 26 strains stored at the Research Center, 83 isolated from soil in Japan and given to them by Dr. Y. Horie, and 40 isolated from soil in Colombia. All the strains were inoculated on brain heart infusion agar medium supplemented with skim milk and incubated at 37°C for 6 days. Clear melting rings appeared around the colonies of only two strains which had been isolated from patients with aspergillosis. When the conidia of the two strains were inoculated intravenously into mice, they affected the mouse brain remarkably within 4 days.
