Effect of a tetracycline antibiotic on the experimental pathogenicity of Cryptococcus neoformans

The pathogenicity of three stains of Cryptococcus neoformans was experimentally tested by intradermal inoculations into albino rabbits and intraperitoneally into mice. A relationship was found between the number of inoculated cells and the diameter of dermal lesion; moreover, a typical kinetics of lesion evolution and healing has been shown. Treatment of rabbits with deoxytetracycline did not dramatically influence the behavior of dermal lesions. However, in experiments dealing with strain Vi selected for its enhanced dermotropism, the antibiotic did significantly provoke a diminition of the inflammatory area. In mice, the antibiotic caused a marked increase in mortality (as evaluated by both LD50 values and rate of mortality). Neither in rabbits nor in mice, however, were we able to detect a significant effect of the drug on the dissemination of C. neoformans cells in internal organs. There is no simple explanation for the reported observations but it is possible that local factors in the derma or an aspecific antiinflammatory action of deoxytetracycline are responsible for the unusual response of dermal experimental infection to antibiotic treatment.