Problems in Experimental Candida Infection of Congenitally Athymic (Nude) Mice

Abstract

There are several conflicting reports related to the susceptibility of congenitally athymic (Nude) mice to the experimental murine infection with Candida albicans. Some workers including present authors claimed that the nude mouse was more susceptible to candida infection while Cutler and Rogers reported to the contrary. Experiments were designed to elucidate the discrepancy among these reports by using C. albicans 9938 which was supplied by J. E. Cutler (Department of Microbiology, Montana State University) and C. albicans 7N which had been maintained in our labolatory. Detailed physiological studies on the properties of the two strains revealed that C. albicans 9938 failed to form typical chlamydospores on the media tested and showed much less ability to form germ tubes in the serum medium. Furthermore, it was found that strain 9938 was approximately one-tenth less virulent than strain 7N and about one-third of cells in inoculum were dead with strain 9938, whereas almost all cells were alive with strain 7N under the condition used by Cutler. The number of low virulent strain 9938 in the kidney, as determined by viable cell count, decreased since the day after infection with nude mice, while the number did not decrease with normal littermates. However, no significant difference was observed between the final survival rates of both groups of mice. On the other hand, no significant difference between mouse strains in the proliferation and disappearance in the kidney, as well as the survival rate, was observed with highly virulent strain 7N. By the histopathological studies, it was revealed that nude mice had a greater ability to clear candida from infected foci in the kidney than normal littermates in the early stage of infection. But with the lapse of time after infection, a strong response of inflammatory cells to candida was observed in normal littermates in contrast with a weak response in nude mice. The above results seem to indicate the importance of selecting proper strains of C. albicans for the determination of the susceptibility of the mouse. The colony forming units in the organs of C. albicans infected mice did not accurately reflect the pathological changes possibly owing to the tangled filamentous growth of C. albicans in the tissue.