Tumors and other lesions induced in germ-free rats exposed to Aspergillus versicolor alone

This investigation was designed to determine whether any lesion would be induced in germ-free animals exposed to Aspergillus versicolor alone. Twenty-one male Wistar germ-free rats bred in our Laboratory were monoassociated by A. versicolor while 20 male germ-free rats of the same strain were used as controls. All rats were maintained on our home-made pellet diet for 2 years. Animals that died or were killed were autopsied and examined pathohistologically. Eighteen of the 21 monoassociated rats (86%) had necrosis in the liver, 16 of them (76%) had foamy cell granuloma in the lung, 11 of them (52%) had fibrosis in the pancreas and 12 of them (57%) had nephron lesions in the kidney, while none of the germ-free control rats had such lesions, indicating that these lesions were induced by A. versicolor. Further, 62% of the monoassociated rats had tumors in the pleura, lung and endocrine organs, while 15% of the controls had tumors only in endocrine organs. It was noted that two of the monoassociated rats developed pleural mesotheliomas and another developed a squamous cell carcinoma in the lung, presumably due to conidiospore inhalation. This investigation showed that A. versicolor, a common mold, at a high concentration in the absence of other microbes, induced severe organ damage and some tumors in rats.