Comparative study of pathogenicity and antigenicity of six Paracoccidioides brasiliensis strains

Abstract

A comparative study of antigenicity and patho-genicity for rats of six Paracoccidioides brasiliensis strains was carried out. The antigenic capacity "in vitro" of cytoplasmic extract from each strain was determined by immuno-diffusion test against 6 serum samples obtained from rats experimentally infected with Paracoccidioides brasiliensis, that had presented positive reactions with a metabolic control antigen. The cytoplasmic extracts were used at final concentration of 100 mg/ml. All of them showed 2 or 3 precipitation bands in this assay. One hundred twenty Wistar rats both sexes weighing approximately 200 g, were inoculated intracardiacally with suspensions of the yeast phase of different P. brasiliensis strains. Two concentrations containing 3x10(7) and 5x10(7) cells/ml of each isolate were prepared. The inoculated animals were divided in two groups, one was left to its spontaneous outcome and the percentages of deaths were registered and the other rats were sacrificed at 14, 28, 56 and 70 days post-infection. The following parameters were taken into account for evaluation: A) presence of macroscopic granulomas in lung, liver, spleen and kidney; B) presence of P. brasiliensis in microscopic exams of the same organs, in wet preparations and in hystologic sections stained by H&E; C) culture of lung and D) immunodiffusion test using pre-mortem serum samples and the homologous antigen. The correlation between the most important parameters studied in each strain are summarized as follow:As no significant differences between the two inocula employed for each strain was observed, the before-mention results are the average of those obtained with each inoculation doses. The most virulent strain was a recent isolate from an acute disseminated form of the juvenil type. A morphological atypic isolate, which produced a very mild experimental infection with viable P. brasiliensis determined 100% of positive immunodifussion tests. The strain 339 did not produce infection in the rats, and the animals inoculated did not presented antibodies. Nevertheless this strain is useful to prepare antigens for Serologic reactions. No correlation between antigenicity or pathogenicity and the time during which these strains were mantained "in vitro" could be established.