Spontaneous aggregation of Streptococcus mitis ATCC 903

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Abstract
Glucose or sucrose grown cells of oral S. mitis ATCC 903 bind spontaneously to the surface of each other producing visible microbial aggregates upon incubation in 10 mM phosphate, citrate-phosphate or tris-maleate buffers. Aggregation was delayed and proceeded at a slower rate when bacteria grown in a culture medium with a low carbohydrate/nitrogen ratio were used. Growth in this culture medium resulted in carbohydrate limitation. The aggregation was highly reproducible and was unaffected by pH in the range of 4.4-7.0 but was decreased at pH 8.0 and completely inhibited at pH 9.0. No inhibition of the reaction was observed when a series of simple and complex carbohydrates were added. There was no significant difference in the rate of aggregation at 20, 30 and 37.degree. C. Aggregation occurred at a demonstrable rate at 0.degree. C. Chloramphenicol did not inhibit aggregation. Since inhibition of aggregation was obtained by treatment of bacteria with trypsin or heat it appears that protein or glycoprotein components on the bacterial surface were involved in the reaction.