A correlative study was made of some structural and functional features of a reasonably synchronized culture of Bacillus cereus strain terminalis during spore formation and maturation. The successive stages of development could be recognized by phase contrast microscopy and in electron micrographs of ultra-thin-sectioned cells. Attempts were made to correlate these changes with the acquisition of heat resistance and the synthesis of dipicolinic acid. The outer coat of the spores was observed to be formed first around the forespore; the exosporium, cortex, and inner coat then appeared sequentially and independently of existing sporangial membranes. Dipicolinic acid synthesis began in the early transitional stage, just after forespore formation, and reached one third of the maximum level before an increase of heat resistance in the population was detectable, indicating the possibility of a correlation only above a threshold level of the compound.

Changes in refractility and optical density occurring in individual spores of Bacillus cereus T and B. megaterium QM B1551 during germination were investigated by use of a Zeiss microscope photometer. The curves revealed that the germination process in single spores had two distinct phases; an initial rapid phase was followed by a second slower phase. Under the experimental condition employed, the first phase of germination of B. cereus spores lasted for approximately 75 i 15 sec, whereas the second phase lasted for 3 to 4.5 min. In B. megaterium spores, the first phase was observed to last for approximately 2 min and the second phase for more than 7 min. The duration of the second phase was dependent on conditions employed for germination. The kinetics of the first phase were strikingly similar under all conditions of physiological germination. Time-lapse phase-contrast microscopy of germinating spores also revealed the biphasic nature of germination. It was postulated that the first phase represents changes induced by an initial partial hydration of the spore and release into the medium of dipicolinic acid, whereas the second phase reflects degradation of the cortex and hydration of the core. MATERLILS AND METHODS Preparation of spores. A phage-resistant strain of B. cereus strain T, isolated from the original strain at the University of Michigan, was grown and sporulated with vigorous aeration in a modified G medium, as reported earlier (6), by use of a Microferm fermentor (model MF-14, New Brunswick Scientific Co., New Brunswick, N.J.). Complete sporulation was usually attained within 10 to 12 hr after inoculation. The free 1011

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The progressive stages in Bdellovibrio bacteriovorus penetration into two strains of Escherichia coli were examined by use of electron microscopic techniques. The initial change observed in the ultrastructure of the host following parasitic attack was the swelling of the cell envelope at the site of attachment. The Bdellovibrio then appeared to pierce the center of this swelling, forming a pore in the outer wall layers of the host. The edges of this entry pore constricted the Bdellovibrio throughout its penetration into the host cell. Although partial disruption of the cytoplasmic membrane was always apparent, the parasite did not appear to actively penetrate through this barrier. An attempt is made to correlate the fine structural changes involved in penetration with the physiological data that have accumulated to date.

The effects of several physical and chemical agents on the survival of Trichophyton mentagrophytes arthrospores were investigated. Although arthrospores of this dermatophyte were highly resistant to chilling and freezing, they were extremely susceptible to moderate heat (above 5000) and desiccation. This high susceptibility could be significantly reduced when they were dried in the presence of exogenous proteins. These arthrospores were markedly susceptible to glutaraldehyde. They appeared to be significantly more resistant than their hyphal counterparts to common antimycotics such as clotrimazole, griseofulvin, miconazole nitrate, and nystatin. Clinical and epidemiological implications of these observations are discussed.