Origin of L Type Colonies in Bacterial Cultures. †

Abstract

Small secondary colonies, corresponding morphologically to young colonies of the L1 strain isolated by Klieneberger from cultures of Streptobacillus moniliformis, have been observed occasionally in cultures of various Gram negative bacteria. 1 In all cultures in which such secondary colonies developed a large number of bacteria swelled up into large deeply stained, spherical or fusiform bodies. It was first seen in a culture of Bacillus influenzæ that occasionally L type of colonies developed from the large bodies. Later this process was observed repeatedly in the cultures of 2 colon bacillus strains.

After 24 hours of growth the colonies of these strains consisted mainly of large spherical bodies. In order to observe the development of these large bodies in these 2 strains different procedures proved to be helpful. The colonies of one strain were very tenacious and when an impression of the colonies was made on blood agar plates only the large bodies, with very few bacteria, were transferred. After 6 to 12 hours fine curved filaments grew from the large bodies into the agar and after 24 hours about two-thirds of them developed into tiny L type colonies. With the other strain a similar process was observed when a broth culture was transferred on blood agar plates after varying time intervals. In the transplant made after 24 hours' growth many large bodies were visible on the agar surface. Only a few bacterial colonies developed in these plates but after 6 to 12 hours the large bodies began to germinate and produced L type colonies. Transplants made from the broth culture after 48 hours, gave only abundant bacterial growth. With either strain, L type colonies developed only at the places where large bodies were present.