Pseudobacteriophage of Bacillus anthracis.

During the examination of some old stock cultures in November, 1924, there was found an agar slant of Bacillus anthracis which had the appearance of undergoing lysis by bacteriophage. The film of growth was interrupted by well defined partly confluent denuded areas, many of them containing small centrally located secondary colonies. Transplants of the culture to agar gave similar appearances after incubation for two days at 37° C. and one or more days at room temperature. Transplants to broth did not show clearing but the plaques again appeared when the broth cultures were transplanted to agar. An older agar slant culture from which the culture first mentioned above had been inoculated did not show plaques nor did fresh transplants of this culture, but when this “negative” strain was inoculated with material from one of the plaques of the “positive” strain plaques appeared in subsequent transplants. Filtrates of broth cultures of the positive strain were inactive when added to the negative strain.

Plaques on agar plates examined under the microscope were found to contain a nucleus of free spores, the remainder to the plaque being made up of pale remnants of bacilli and amorphous granular detritus. The matrix of growth surrounding the plaques was composed of typically curled but apparently sporefree anthrax filaments. Fishings from the centers of plaques yielded cultures of typical sporulating Bacillus anthracis. Fishings from the matrix yielded cultures of non-sporulating bacilli otherwise like B. anthracis, hereafter referred to as the nonsporulating strain.

After prolonged growth on agar, on potato or in broth at 37°C. and at 20°C. the non-sporulating strain failed to produae visible spores and did not resist heating for twenty minutes at 75°C. Cultures of this sporulating strain resisted similar exposure to heat.