The Isolation of L Type Cultures from Bacteroides with the Aid of Penicillin and Their Reversion into the Usual Bacilli

Publisher Website
Google Scholar
Abstract
The growth of 6 Bacteroides strains was studied on ascitic agar plates containing from 1 to 5,000 U. of penicillin per ml. of the medium. Growth in the usual bacillary forms was inhibited and L type colonies developed in abundance in 2 strains with all concns. of penicillin. A few such colonies developed in plates inoculated with 2 other strains and none on those inoculated with the remaining 2 strains. The processes induced by penicillin resulting in the growth of L type colonies are similar without the use of penicillin. The bacilli, in a culture of the previously studied strain 132 after loss of pleomorphism, were induced by penicillin to swell to large forms. In the early stages of transformation these large forms transferred to penicillin-free media returned to the usual bacillary form; in a later stage they produced only L type colonies. The L type colonies of two strains were induced to grow in thioglycolate broth. After prolonged incubation (4 to 64 days), the usual bacilli reappeared in all broth cultures. On agar plates development of bacilli was never observed in L type cultures. Before the L type cultures were inoculated into broth, they were transplanted on agar for a sufficient number of times to exclude the presence of bacilli accidentally included in them. The L type of growth in Streptobacillus moniliformis and that in Bacteroides are similar not only in their derivation from bacilli, in morphology, and in high resistance to penicillin, but also in the fact that, under appropriate conditions, they reproduce the parent bacilli in a similar way.