Abstract
During a study made on the typing of local strains of B. typhosus, colonies of various appearances were noted on plating of these old cultures. This afforded the opportunity of determining by the bacteriophage-typing technic 1 whether or not various kinds of colonies derived from a parent stock culture would belong to the same type of V-forms. The observations made regarding this point are here-with communicated.
A collection of 79 strains of B. typhosus reported previously 2 was studied. These cultures were kept in semisolid agar media for 3 months to 1 1/2 years with subculturing every 3 months. Upon spreading of these stock cultures on nutrient agar plate (1.5% agar, pH 7.6) followed by incubation at 37°C for 16-20 hours the following kinds of colonies were encountered:
All normal and variant colonies have smooth surfaces and their suspensions in 0.9% saline are stable. They, however, vary greatly in regard to the colony outline, opacity and size. Thus the colony outline may be smooth and round or irregular, rough with fan-like margin, the opacity may be opaque, mosaic or with varying degrees of translucency and the colony size may vary from 1 to 5 mm in diameter. On repeated subculturing the variant colonies showing irregular margins may become smooth and round, and the translucency or mosaic appearance may revert to that of normal opacity. Thus no complete or stable rough colonies have been encountered. These colonies may be regarded as colony variants probably degradation of S form with varying degrees of roughness.
Of 79 strains studied, 27 strains gave only the normal colonies, 3 strains only the variant colonies and the remaining 49 strains gave mixtures of normal colonies with one or more kinds of variant colonies.
Get full access to this article
View all access options for this article.