THE DEVELOPMENT OF PROTEUS CULTURES IN THE PRESENCE OF PENICILLIN

Abstract

An interesting effect of penicillin was observed in agar plates containing the antibiotic and inoculated with Streptobacillus monilifoimis and Bacteroides (Dienes, 1948c). The cultures of these species undergo a peculiar transformation under certain conditions. The bacilli swell into large round forms, the culture autolyzes, and a new growth appears that is similar in appearance and mor-phology to the pleuropneumonia group of organisms. Penicillin greatly favors this transformation. In the absence of penicillin only a few pleuropneumonialike colonies develop among the bacterial colonies; when penicillin is incorporated in the media, such colonies grow abundantly in pure culture. Some Bacteroides strains that do not produce pleuropneumonialike colonies without penicillin produce them abundantly on penicillin plates. It became apparent when the experiments were extended to other species that penicillin exerts a similar effect on many gram-negative bacilli. Pleuropneumonialike colonies have been iso-lated with the help of penicillin from Proteus (Dienes, 1948a), Hemophilus influenzae (Dienes, 1947), and Eberthella typhosa (Dienes, 1948b), from several