Conversion of group B streptococci to the L-phase: Physiological and immunological characterization

Seven strains representative of the five serotypes of group B streptococci were converted to the L-phase by means of penicillin in a liquid medium. The conversion and adaptation to growth in the L-phase of the group B, type III strain 76-043 were studied in detail. This L-phase has been subcultured serially 204 times in liquid medium containing penicillin. Stability of the L-phase was evident by 195 serial subcultures in the absence of penicillin without reversion to the parent bacterial phase. Studies of the kinetics of growth in the cell-wall-defective state showed a lack of correlation between the number of viable units and the turbidity of the culture, as well as a rapid decline in the number of colony-forming units once the minimum pH of the culture was reached. Addition of Na₂HPO₄ or K₂HPO₄ to the growth medium did not prevent the sharp decline in the number of viable units. Group B and type III antigens continued to be detected in culture supernatants but not in HCl extracts of cells of the L-phase of strain 76-043. These immunological markers confirmed the precise bacterial origin of the L-phase.