The growth rate regulates the composition and density of the fibrillar coat on the surface ofStreptococcus salivariusK+cells

Aggregation of 27 oral bacteria by human whole saliva. Influence of culture medium, calcium, and bacterial cell concentration, and interference by autoaggregation

Twenty-seven oral strains of the genera Actinomyces (5), Bacteroides (3), and Streptococcus (19) were tested for aggregation by human whole saliva, as well as the effect of culture medium, Ca-ions, and bacteria concentration thereupon. Of the media tested, GF-broth gave rise to less interference by autoaggregation or higher aggregation titers than BHI and TSB, and was used throughout this study. In most cases, Ca-ions (1 mM) only enhanced the rate of induced aggregation, whereas raising the bacteria concentration increased the rate of both induced- and autoaggregation. The final titers, ranging from 1-64, were hardly affected by these parameters, except those of S. rattus HG 59 and S. mutans HG 199, which were respectively increased and decreased by Ca-ions. Saliva-induced aggregation was observed for 21 strains of A. viscosus, A. naeslundii, A. israelii, B. gingivalis, B. intermedius, S. cricetus, S. mutans, S. rattus, S. sanguis, and S. sobrinus, mostly within 15 min to 3 h. Seventeen of these strains also showed autoaggregation, usually well after the onset of induced aggregation. Any potential induced aggregation of B. gingivalis HG 91 was always masked by autoaggregation, as well as that of the S. mutans strains under a particular set of conditions. The aggregation rate and titer varied considerably in a mutually unrelated and strain-dependent way. These microtiterplate data were matched by the 5 spectrophotometric patterns observed for saliva-bacterial interaction, which moreover, gave the better differentiation between induced and autoaggregation. In conclusion, most strains tested can show rapid saliva-induced aggregation in a strain-dependent way, yet strongly affected by the experimental conditions and interference from autoaggregation.

Fermentation products, amino acid utilization, maintenance energies and growth yields for the fibrillar Streptococcus salivarius HB and a non-fibrillar mutant HB-B grown in continuous culture under glucose limitation

The fibrillar strain Streptococcus salivarius HB and a non-fibrillar mutant, strain HB-B, were grown in a defined medium under glucose limitation in a chemostat. Fermentation balances were produced for both strains in batch culture and at growth rates between 0.1/h and 1.1/h. In batch culture both strains fermented glucose to lactate, but in continuous culture glucose was fermented to formate, acetate and ethanol with increasing amounts of lactate as the growth rate was increased. Lactate never became the major fermentation product even at the highest growth rate. Amino acid analysis showed that only lysine was more than 50% utilized, while proline and tyrosine showed net production. The non-fibrillar strain HB-B showed, in general, a reduced utilization of amino acids compared with the fibrillar strain HB. Calculated growth yields and maintenance energies for the two strains showed that there was a reduction in the true growth yield and the maintenance energy coefficient of the non-fibrillar strain HB-B when compared with the fibrillar strain HB. The increase in the maintenance energy of the fibrillar strain HB (1.382 mmol/g/h) when compared with the non-fibrillar strain HB-B (0.546 mmol/g/h) of 153% is proposed to be the energy required for the maintenance of the fibrillar surface of the cell.