Factors affecting the survival of Neisseria sicca

Cultures of Neisseria sicca incubated at 37 degrees C died rapidly (within 36 h) after growth ceased. Re-suspending cells in a brain heart infusion broth and storing at 4 degrees C greatly reduced the rate of decline in viability (decimal reduction time 6 days). An important factor in maintaining viability was apparently the presence of external energy source(s). Survival comparable to that in broth was obtained by incubation in Ringer's solution with pyruvate plus glucose (but not with pyruvate or glucose alone). Medium pH had little effect on survival in the range pH 7.0 to 8.5. Energy sources also promoted survival of cells in Ringer's solution or a buffered salts solution at 37 degrees C. Highest levels of survival (up to 30% at 24 h) were obtained with pyruvate, lactate, proline and glutamate. A number of other amino acids and the tricarboxylic acid cycle intermediates, isocitrate, oxoglutarate, succinate, fumarate, malate and oxaloacetate, enhanced survival to a lesser extent.