Spontaneous aggregation of Streptococcus mitis ATCC 903

Abstract

– 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.

Rapid labelling of bacteria with [14C]palmitic acid and its application in an aggregation assay

“…The modification of the bacterial surface by heat, trypsin and/3-galactosidase treatment did not reduce or enhance the amount of bound fatty acid as compared to unmodified bacteria. These treatments change the surface properties of S. mitis ATCC903, as indicated by inhibition of aggregation of this strain [1]. However, the results emphasize the importance of keeping a constant pH and avoiding the use of detergents during labelling and subsequent experimental procedures.…”

“…S. mitis is known to undergo homotypic aggregation, i.e. the bacteria bind to cells of the same species forming large visible aggregates [1]. After incubation of labelled S. mitis for 90 min, the cells have sedimented to the bottom of the tube and only free fatty acid remains in the upper part of the suspension.…”

“…To demonstrate the usefulness of the labelling procedure, labelled bacteria were used in an aggregation assay of S. mitis ATCC903. This strain was chosen because of its ability to aggregate spontaneously [1]. The bacteria were first suspended in [14C]palmitic acid and shaken at 37°C in a water bath for 5 min as described in MATERIALS AND METHODS.…”

Development of aggregating ability in cells of Streptococcus mitis ATCC 903 grown under glucose‐limiting conditions in continuous culture

“…Strains of other oral streptococci, e.g. S. mitis and S. sanguis, may display homotypic aggregation which is not mediated by dextran (1,20). Although S. mitis is one of the dominating species in the dental plaque (9, 10) very litde attention has been paid to the possible importance of this organism in plaque ecology.…”

“…We have previously described some characteristics of homotypic aggregation of S. mitis ATCC 903 (1). Cells growri io batch cuiture where growth was limited by exhaustioo ofthe carbon source (glucose or sucrose) displayed a reduced abiiity to aggregate.…”