Variability of Tubercle Bacillus. I. Mucoid Phase of the Human-Type Strain H-37

The characteristic attributes of both the rough and the smooth phases of the human tubercle bacillus have been amply recorded, but there has been no indication of the existence of a mucoid phase such as occurs in the dissociative pattern of many other microörganisms. 1 The isolation and subsequent growth of a mucoid phase in the human tubercle strain, H-37, is therefore briefly presented.

The parent strain was a stock culture of H-37 (intermediate rough phase) on Petragnini egg-medium kept under paraffin seal at room temperature 4 months. The growth was dry, rough, crumbly; the organisms were pleomorphic rods, some being hooked or curved, others showing Y-formation or lateral budding. Many rods contained large granules and all organisms were strongly acid-fast.

The first experimental transfers from this growth were made to 3 liquid mediums: (1) a synthetic medium, pH 7.2, (2) 5% glycerol broth, pH 7.6; (3) a double-strength veal-infusion broth, resterilized, with 2% neopeptone (Difco), 5% glycerol, 0.04% asparagin-1, pH 8.0. The transfers were made, not to the surface, but to the bottom of each flask of liquid. In the first 2 mediums the growth was very slow and finely granular, with no later turbidity or pellicle-formation. The organisms were coherent or discrete beaded acid-fast rods. Repeated transfers from these mediums to a variety of solid mediums produced the dry, rough growth only, typical of culture H-37 containing short acid-fast rods.

The growth in neo-peptone glycerol-broth, pH 8.0, at first resembled that in the other 2 mediums. On the 9th day of incubation at 37°C, however, there developed a slight cloud above the granular growth, and on the 10th day the fluid was turbid. A needle withdrawn from the fluid carried with it material that formed a filament 2 feet long before snapping from the surface of the broth.