Varieties of Acid Fast Bacilli and Their Relationship to Disease in Man

Less than a century ago it was found that leprosy and tuberculosis were due to bacteria which, when stained, could not be decolorized, even with acids. Since that time many other kinds of acid fast bacilli have been discovered. Some of these are parasites which evoke disease only in man or in man and other mammals. Some cause lesions in various warm or cold blooded animal species while others are entirely saprophytic, living freely on animal secretions or excretions, on plants, or even in soil, water and other inanimate materials. Recognition of the differences between the various mycobacterial species have been greatly facilitated by recently introduced methods for their investigations. The acid fast bacillus of human leprosy, M. leprae, was described a decade before the discovery of the tubercle bacillus. Differences in the form and staining properties of these two kinds of acid fast bacilli were pointed out by Koch in his original presentation in 1882. The bacillus of rat leprosy, or Stefansky’s bacillus, is a similar acid fast organism which is found in smears or sections from nodules or other lesions in rats or mice. Neither the human nor the rodent leprosy bacilli have yet been successfully cultivated, and the various acid fast and other bacteria which have been obtained from leprous lesions are probably contaminants, and not the cause of the disease. The bacillus of bovine enteritis, or Johne’s bacillus, is an acid fast organism which may be cultivated from intestinal discharges or other specimens from affected cattle or sheep only after long incubation on complex media to which has been added an extract of killed mycobacteria. Myco bacterium ulcerans is another acid fast bacillus which does not grow under the usual bacteriological techniques. It may be cultivated on glycerol-free medium at temperatures below 33#{176}C, but not in the ordinary incubator temperature of 37#{176}C. It was first found in ulcerative skin lesions in men and animals in Australia, and later in other countries. M. balnei is an acid fast bacillus which also grows best at temperatures lower than that of the human body, though it may be adapted to grow at 37#{176}C. It has been found in keratotic skin lesions in persons using certain swimming pools, and from the water or sides of the pools in some instances. Acid fast bacilli which have been seen in skin lesions, lymph nodes and other materials from tuberculin reacting cattle and guinea pigs but which have not been successfully cultivated might have grown, in some instances, if special cultural techniques had been used. All acid fast bacilli are also alcohol fast, and therefore apparently gram positive, non-sporulating, non-encapsulated, non-motile, and non-branch-