Filamentous forms of Streptococcus cremoris and Streptococcus lactis. Observations on structure and susceptibility to lysis

Abstract

Filamentous cultures of Streptococcus cremoris and Streptococcus lactis were isolated from growth which formed in orifices of medium inlet tubes of chemostats. Filamentous variants were maintained by biweekly transfer in agar stab cultures. Bacteria from parent and filamentous cultures grown in broth had the same DNA base content and the same bacteriophage susceptibility. Electron micrographs showed that filamentous streptococci had apparently normal cell walls and slightly enlarged cross walls. Filaments appeared to result from failure of daughter cells to separate after division. Filamentous cells were less readily autolyzed and were less susceptible to lysis by Iysozyme than normal cells. The results suggest that filament formation in lactic streptococci was associated with lower autolysin activity.