– Glucose or sucrose grown cells of Streptococcus mitis ATCC 903 bind spontaneously to thesurface 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 ration were used. Growth in this culture medium resulted in carbohydrate limitation. The aggregation was highly reproducible and was unaffected by pH in therange 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. The was no significant difference in the rate of aggregation at 20,30 and 37°C. Aggregation occurred at a demonstrable rate at 0°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.
Abaas. S. & Holme. T. Ion interactions in the aggregation of streptococcus mitis. Acta path. microbiol. immunol. scand. Sect. B, 91: 31 1-316. 1983.Spontaneous aggregation of Sireprococcus miiis ATCC 903 was highly dependent on various electrolytes such as sodium chloride, sodium phosphate or potassium phosphate with an optimum at I0 mM concentration. No aggregation was obtained in distilled water. Addition of a number of mono-or divalent ions to bacteria incubated in 10 mM phosphate or tris-maleate buffers resulted in an inhibition of aggregation. A 50% inhibition of aggregation was obtained at low concentrations of calcium, magnesium, sulphate and carbonate ions. Other mono-and divalent ions tested were needed in significantly higher concentrations in order to obtain the same inhibition. Aggregation inhibition by calcium or magnesium salts was reversed by chelation with EDTA. Washing bacteria previously treated with magnesium or calcium salts resulted in a complete recovery of aggregating ability. Spontaneously aggregated cells were completely dissociated at 10 mM magnesium sulphate or I00 mM sodium chloride. The results indicate that electrostatic interactions are of major importance for aggregation of S . mitis ATCC 903 whereas hydrophobic interaction plays a minor role.
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