ION INTERACTIONS IN THE AGGREGATION OF STREPTOCOCCUS MITIS

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Abstract
Spontaneous aggregation of S. mitis ATCC 903 was highly dependent on various electrolytes such as NaCl, NaH2PO4 or KH2PO4 with an optimum at 10 mM concentration. No aggregation was obtained in distilled H2O. Addition of a number of mono- or divalent ions to bacteria incubated in 10 mM PO43- or tris-maleate buffers resulted in an inhibition of aggregation. A 50% inhibition of aggregation was obtained at low concentrations of Ca2+, Mg2+, SO42- and CO32. Other mono- and divalent ions tested were needed in significantly higher concentrations in order to obtain the same inhibition. Aggregation inhibition by Ca or Mg salts was reversed by chelation with EDTA. Washing bacteria previously treated with Mg or Ca salts resulted in a complete recovery of aggregating ability. Spontaneously aggregated cells were completely dissociated at 10 mM MgSO4 or 100 mM NaCl. Thus, electrostatic interactions are of major importance for aggregation of S. mitis ATCC 903; hydrophobic interaction plays a minor role. [Aggregation plays a role in the development of dental plaques.].