FIG. 5.

Ammonia production and its effect upon survival in Alt. 1 and Alt. 2 cultures. (A) S. pyogenes strains CS101, Alt. 1, and Alt. 2 were grown to stationary phase in static TH broth cultures under a 5% CO₂ atmosphere. Early-stationary-phase culture samples were removed and filter sterilized, and ammonia concentrations were determined. For this graph, T₀ is entry into stationary phase (OD₆₀₀ of ∼1.0). The concentration of ammonia present in sterile TH broth is represented by the bar at the left marked “TH.” Each bar represents the mean value from at least three independent cultures. The error bars are the standard deviations from the means. (B) S. pyogenes strains CS101, Alt. 1, and Alt. 2 were grown to stationary phase in static TH broth cultures under a 5% CO₂ atmosphere. Approximately 24 h after entry into stationary phase, exogenous ammonia was added from a 2 M stock to yield a final culture concentration of 20.0 mM, 10.0 mM, or 5.0 mM. Survival was assayed by spotting 50-μl culture samples on TH agar plates at 24-h time intervals, postentry into stationary phase. The formation of any S. pyogenes colonies within the culture spot was scored positively for survival. The lower limit of detection was 20 CFU per ml. Bars represent the mean duration of survival for each culture condition. For this graph, T₀ corresponds with entry into stationary phase. The pH range for each culture condition (pH_i), measured after the addition of exogenous ammonia, is noted next to each survival bar. Each data set is the mean of at least four independent cultures. Error bars represent the standard deviations between these experiments.