The susceptibility testing of 13 strains of Mycobacterium leprae to rifampicin and the determination of minimal effective dosage.

By use of the mouse footpad technique, the susceptibility testing of 13 strains of Mycobacterium leprae to rifampicin (RFP) and the determination of minimal effective dosage (MED) were carried out. Among these strains of M. leprae, 8 were obtained from previously untreated multibacillary leprosy patients and 5 from relapsed leprosy patients without using RFP previously. The results showed that the MED of all strains to RFP were less than or equal to 0.001% FRP in the diet, 5 strains being equal to 0.001%, 5 less than or equal to 0.0001%, 2 greater than or equal to 0.0003% and 1 less than or equal to 0.0003%. The results indicated that the MED value of RFP could be lower than that of other reports. Because the critical concentration of RFP for assessment of RFP-resistant strains is not well established a further study would be worthwhile. The results of the determination of sera RFP concentrations in mice administered the RFP diet were identical with that of Holmes' report. Five of the 13 strains also showed that the growth of bacilli were suppressed by 10 mg/kg RFP using the gavage method.

Preliminary observations on experimental leprosy in tupaias (Tupaia belangeri yunalis).

The Tupaia belangeri yunalis (tree shrew) is one of the primitive primates. They were inoculated subcutaneously in the footpad or intravenously with Mycobacterium leprae from a patient with multibacillary leprosy. As controls, the footpads of CFW mice were inoculated with the same suspension of M. leprae. The results showed growth of acid-fast bacilli (AFB) in the footpads of locally inoculated CFW mice and in the footpads of both locally and intravenously inoculated tupaias. Whereas the numbers of AFB declined in the footpads of CFW mice after 12 months, they increased in the tupaia footpads, up to 2.44 x 19(9) AFB/g of tissue. The footpads of one tupaia were swollen, which on section revealed a granulomatous infiltration, including foamy and heavily infected macrophages. M. leprae were also seen in the branches of cutaneous nerves. Also AFB occurred in some viscera. Preliminary studies indicate that the AFB multiplying in tupaias are M. leprae.

[Multiplication of mycobacterium leprae in nude mice].

This article reported the multiplication of mycobacterium leprae in immune-deficient animals-nude mice (NIH/nu/nu). Mycobacterium leprae taken from multibacillary leprosy patient were inoculated with 1.0 x 10(4)/foot pad into right hind foot pad(FP) of nude mice and CFW mice. The results of bacterial enumeration showed that acid-fast bacillus (AFB) in the nude mice continuously multiplied. At 21 months after inoculation, the numbers of AFB increased by over 108,000-folds and reached greater than 1.08 x 10(9)/FP (greater than 5.4 x 10(10)/g tissues), while the CFW mice developed only 3.68 x 10(6)/FP and exhibited their characteristic limited growth pattern. It is indicated that the phase of logarithmic growth was prolonged in nude mice. The AFB multiplied were identified as mycobacterium leprae by following identification test: (1) failure to growth on artificial media; (2) loss of acid-fastness by pyridine extraction; (3) typical growth curve of mycobacterium leprae in foot-pad and sensitivity to antileprosy drugs. The histopathological examination of nude mice foot-pad inoculated were found lepromatous lesions, in which enormous numbers of AFB were seen on 476 days postinoculation, AFB disseminated into the fear, nose, sciatic nerve, testicle, lymphnodes, liver, spleen, lung, and noninoculated foot-pad. As mentioned above, it is considered that experimental leprosy was established in nude mice.