A STUDY ON EXPERIMENTAL MYCOBACTERIOSES PROVOKED BY ATYPICAL MYCOBACTERIA

Abstract

The therapeutic effects of three combined antituberculous regimens were evaluated in vivo for conventional mice (dd white strain) infected intravenously with Mycobacterium intracellulare, TMC 1469 strain. The three regimens evaluated were SM·PAS·INH, KM·EB·INH and KM·RFP·TH·CS·EB, which were all administered to the animals in dosages roughly comparable with clinical use except INH. Successive viable units of bacilli in the right lungs as well as in the spleens of mice were counted on 1% Ogawa media using 10-fold dilution technique of the homogenized organs at one, three, six, nine and fifteen weeks after challenge of the bacilli, while the administration of the drugs was continued for eight weeks, in six days a week, starting one week after challenge. The histopathological findings were observed in gross pathology and in histologic sections of lung, liver, spleen and kidney as well.
The control untreated mice retained ca.4-5×10⁴ viable units of bacilli in 10mg of spleen during entire experimental period, while the viable units of bacilli in lung spontaneously regressed to roughly one fifth of the count at the end of the experiment, which was ca. 1.6×10³ at the start of the treatment. In spleen, the treatments of all three regimens resulted in considerable decrease of viable unit of bacilli as the treatments went and the viable units of bacilli in 10mg of the organ were roughly one fifteenth in the regimen SM×PAS×INH, one tenth in KM×EB×INH and one hundredth in KM×RFP×TH×CS×EB, respectively of the count at the time immediately before treatment. In lung, the difference in the decreases of the viable units of bacilli was less among the three regimens in the range of one twentieth to one fortieth, though the counts went down more rapidly compared with the successive counts of the control untreated group of mice.
Minimal or moderate therapeutic efficacy was obtained at least in the regimen of KM×RFP×TH×CS×EB, however ca. 8×10² viable units and ca. 7×10³ viable units of bacilli still remained in lung and spleen, respectively, at the time of discontinuation of the treatments. Moreover, the gradual increase of the bacilli after the discontinuation of the treatment observed in the final period of the experiment suggested that even the five-drug regimen of KM×RFP×TH×CS×EB was not potentenough to manage M. intracellulare infection.
The main histopathologic findings of the organs of mice infected with TMC 1469 strain were thickening of alveolar septa, peribronchial cell infiltration, microglanuloma in lungs and both mononuclear cell aggregates and multiple minute granulomas in liver and spleen. No significant differences were noticed among the untreated and three treated groups.
Mycobacterium intracellulare, TMC 1469 strain, used in this study was one of the strains which were kindly provided by the U.S.-Japan Cooperative Medical Science Program-NIAID in 1975. The brochure which was simultaneously provided by NIH described the colony morphology of the strain as smooth, pyramidal, thick center, transparent entire edge. The colony morphology which was again observed by us at the time immediately after the challenge to mice confirmed thin transparent colony in 15.8% and the remaining colonies showed thick opaque dome-shaped type.