Myocardial positron tomography with manganese-52m

The biodistribution of radiomanganese (54Mn) was studied in mice, rats, and dogs. Disappearance of radioactivity from the blood was extremely rapid, with a half-time of approximately 0.8 minutes. This resulted in very favorable myocardium-to-blood ratios, even at early times after administration. The myocardial uptake in dogs was greater than 3% at three and 15 minutes, with myocardium-to-blood ratios of about 40:1 at 15 minutes. Positron tomograms obtained with 52mMn clearly demonstrated regional myocardial perfusion. There was good correlation (r = 0.89) of microsphere-to-radiomanganese distribution in the infarcted dog heart.

The pleiotropic effect of spontaneous single-step variant production in Mycobacterium intracellulare

A strain of M. intracellulare, AT 13786, derived from human sputum, gave rise to transparent and opaque colony forms which were cloned and investigated. From the results the conclusion was drawn that the opaque form was a mutant of the transparent type and possessed alterations in the cell envelope which were responsible for enhanced permeability. The opaque form was more susceptible to a number of antibiotics; it grew faster in standard medium, and was not dependent on tween for dextrose utilization. Tween enhanced the antibiotic susceptibility of the opaque form more than that of the transparent. The avirulent opaque colony form of the pathogenic strain serotype Boone also revealed a loss of tween dependence for dextrose utilization. The significance of the overall change has been discussed with respect to the question of virulence.

Permeability barrier to rifampin in mycobacteria

A strain of Mycobacterium intracellulare that exhibited natural resistance to rifampin was isolated. The ribonucleic acid polymerase was found to be susceptible to rifampin. Studies with Tween 80 suggested that a permeability barrier against rifampin was present in the intact organism. A type strain of Mycobacterium smegmatis, ATCC 607, considered resistant to rifampin also demonstrated a permeability barrier. The possibility that rifampin resistance in naturally occurring strains of mycobacteria and variable levels of resistance in strains of certain species of this organism are due to permeability barriers is discussed.