Mechanism of Production of Candida Lesions in Rabbits

Abstract

PLATES X AND XIT H E respiratory tract is exposed to Candida albicans when this organism colonises the mouth, but serious lung infection rarely occurs. Whether this is due to the low virulence of the organism or to its rapid dispersal from the lungs is not known. Felisati, Bastianini and de Mitri (1959) and Aoyama and Ata (1961) produced lesions in the lungs of rabbits by intratracheal injection of C. albicans, but Kurotchkin and Lim (1933) obtained lung lesions only after sensitising the rabbits previously with injections of killed organisms.The present experiments were undertaken to clarify the pathogenic effects and mechanism of disposal of C. albicans when instilled directly into the lungs in high doses. MATERIALS AND METHODSMale rabbits weighing 13-2 kg were used. C. albicans, strain PCI/501/9 isolated from the sputum of a patient and known to be pathogenic for mice, was grown in Sabouraud's glucose broth cultures at 25°C for 24 hr. The cultures were centrifuged and the organisms re-suspended in normal saline. The suspension consisted only of yeasts with no mycelium, and was adjusted to contain 5-10 x 107 cells per ml by haemocytometer count. Methuh of inoculation.Rabbits were anaesthetised with ether and 1 ml of a saline suspension of yeasts was injected directly into the trachea exposed through a short skin incision in the midline of the neck. After injection, the animal was held upright for about 5 min. In one group of 29 rabbits the suspension contained 5 x 107 and in the other 108 organisms per ml. The animals were killed with ether at intervals after injection of 15, 30 and 45 min., 1, 2, 3,4, 6, 8, 12, 24, 48, 72 hr, 4, 5, 6, 7, 8, 9, 10, 12 days and 2, 3, 4, 5, 6, 7, 8, 9 wk. They were immediately dissected, and portions of lung, liver, spleen, pancreas, heart and kidney inoculated into Sabouraud's medium. The remaining portions of the organs were fixed in 10 per cent. formalin, and parailk sections were stained with haematoxylin and eosin, or by the periodic acid-Schiff method, or, where necessary, with haematoxylin and silver methanamine. The morphological forms of C. albicans in tissue-yeast- RESULTS Mortality.None of the 29 rabbits that received 5 x 107 organisms died. There were three deaths among 29 rabbits that received 108 organisms. Of these, one died with extensive bronchopneumonia and bronchial necrosis 48 hr after injection; one died with severe lesions in the liver and kidney after