The Effect Of Rifampicin And Dapsone On Experimental Mycobacterium Leprae Infections: Minimum Inhibitory Concentrations And Bactericidal Action

Abstract

STUDIES on the chemotherapy of experimental human leprosy were made possible in 1960 by the demonstration of a limited infection with Mycobacterium Zeprae in the mouse footpad (Shepard, 1960). To begin with they were based mainly on the continuous administration of drugs from the day of inoculation, and subsequent assessment of their ability to suppress the growth of small inocula of M. Zeprae Chang, 1962, 1964;Rees, 1965;Gaugas, 1967). These studies were later extended by an assessment of the therapeutic action of drugs on established infections (Shepard and Chang, 1967), the viability of the organisms after drug treatment being tested by the tedious procedure of subinoculation into new groups of mice. Shepard (1967~) reported a " kinetic " technique of detecting the bactericidal action of drugs based on the treatment of inoculated mice for a limited period and measuring the subsequent delay in growth of the leprosy bacilli. Any delay exceeding that accounted for by bacteriostasis during administration and subsequent excretion of the drugs is taken to indicate that the growth must have developed from a number of viable bacilli smaller than that inoculated and hence that there has been a bactericidal effect. Results obtained with this technique suggested, for example, that dapsone is bactericidal to M . Zeprae, but only after 60 or more days of treatment (Shepard, 1967a.Rifampicin, a recently synthesised derivative of rifamycin, has been shown to be active both in vitro and clinically against M . tuberculosis, with bactericidal action (Grumbach and Rist, 1967;Pallanza et al., 1967;Verbist et al., 1967). When tested in the mouse footpad system it was found to be highly active against M. Zeprae (Rees, Pearson and Waters, 1970;Hilson, Banerjee and Holmes, 1972). The minimal effective dosage of the drug was, however, not determined.The present paper reports the activity of rifampicin against three strains of M. leprae in the mouse footpad by continuous administration, and a comparison between dapsone and rifampicin by means of the kinetic method of Shepard. MATERIALS AND METHODSThe approach employed was to follow the growth of M . leprae in the footpad of control and of drug-treated mice, according to the method of Shepard and Chang (1962).

Rifampicin: The Investigation of a Bactericidal Antileprosy Drug

“…A very rapid fall in the MI (to baseline values within 4 weeks) was observed in our initial, pilot, clinicai trial, implying that the drug possessed powerful bactericidal activity (Rees, Pearson and Waters, 1970). These experimental findings have been confirmed and extended by Holmes and Hilson, 1972;Shepard et aI. , 1971 andFasal, 1972a,b).…”

Characterization of the heat shock response in Mycobacterium bovis BCG

“…M. bovis BCG (Pasteur strain) was grown at 37°C in Dubos broth base supplemented with 10% Dubos medium albumin (Difco) and harvested in mid-exponential-phase growth at a density of 2 x 108/ml. Mycobacteria were counted by the method previously described (6).…”

Susceptibility of Mycobacterium Leprae to the Bactericidal Activity of Mouse Peritoneal Macrophages and to Hydrogen Peroxide

“…leprae had been passaged were also used. Tissue was homogenised in glass grinders in saline containing albumin 0-1%, and bacilli were counted by the method of Holmes and Hilson (1972) with a PTFE-coated microscope slide (C. A. Hendley (Essex) Ltd). The number of acid fast bacilli/circle diameter was counted and used in conjunction with the calibration of the microscope field to calculate the number of bacilli/ml of suspension.…”