Abstract
An acid-fast organism isolated by Chapin 1 from a leprous rat in 1912 has been kept in the culture collection of the National Tuberculosis Association for considerable time. Transfers distributed over the country from this and other sources have been designated as “bacillus of rat leprosy”, mycobacterium of “rat leprosy”, “rat leprosy bacillus”, etc. This mycobacterium is probably not identical with acid-fast organisms in tissue from actually leprous rats. 2 , 3 , 4 , 5 These observers found it very difficult, if not impossible, to cultivate the organisms but stated that the disease could be transmitted from rat to rat by injecting infected tissue. The organism under discussion was received some years ago from the National Tuberculosis Association and labelled “Rat leprosy bacillus No. 368”. It grows luxuriantly on Petroff's or Lowenstein's egg medium (pH 7.4) after an incubation of about 4 days. The growth membrane appears deeply orange colored. Growth also takes place on slants of nutrient agar containing no glycerol at pH 7.4, but acid-fast properties are lost after a week of incubation on this medium. Such properties may be regained after planting on the egg media which contain glycerol. The organisms measure from 0.3 to 3.0 mu. in length and about 0.3 mu. in breadth. Numerous granules have been observed on acid-fast and gram-stained preparations. The organism is acid-fast and gram-positive.
After several transfers on petri plates of Petroff's egg medium one of these cultures, initially R in character, was incubated for several weeks at 37.5°C. Upon examination, typical S colonies as well as the usual R colonies were found. The S colony is smooth, round, domed and glistening moist in appearance, and measures 1/2 to 2 mm.
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