Abstract
The successful colonial growth of leptospirae was accomplished with many strains under the microaerophil condition. The colonial growth was more distinct under the microaerophil condition than under the aerophil one, although the colonies of some strains developed aerobically. Patterns of suitable microaerophil conditions present differences among strains. Strains of the same serotype occasionally showed different microaerophil character. Specific range of CO2 requirement was observed in certain serotypes. Of the 5 strains of L. aulumnalis, 4 formed colonies only in a small amount of CO2. Colonial growth of L. icterohaemorrhagiae usually succeeded in closed dishes or in 1% CO2 and not under a supply of more than 3% CO2. The colony type of many strains was usually round, while mosaic or pin-head colonies were observed in some strains. These were considered specific to each strain. Size or figure of the colony of same strain, however, varied with the atmospheric condition. Generally, colonies were larger and thinner in air, while they were smaller, thicker and clearer under the microaerophil condition as the CO2 concentration increased. Leptospiral cells proliferated hemispherically into the solid medium and never on the surface of the medium, irrespective of aerophil or microaerophil incubations or of the agar content of the medium. The characteristic development and figure of the colonies were sufficiently specific to leptospirae. From these findings, microaerophil incubation is considered to be one of the most important factors for the colonial growth of leptospirae.
