The classification of the oral streptococci has long remained a difficult area of streptococcal taxonomy. This article reviews the current classification of these bacteria into four species groups, and each group is described in detail. The often confusing changes that have taken place in the classification, identification and nomenclature of the member species are reviewed against a historical background of gradually improving techniques and approaches, leading towards a natural classification based primarily on genotypic evidence. Identification schemes currently in use employing biochemical tests are also reviewed, together with alternative molecular approaches.

The associations of Streptococcus intermedius, S. constellatus, and S. anginosus (the three species of the S. mileri group) with clinical infections and sites of isolation were investigated by using a simple biochemical scheme to identify a collection of 153 clinical isolates. S. intermedius was associated with abscesses of the brain and liver, while both S. anginosus and S. constellatus were isolated from a wider range of sites and infections. S. anginosus strains predominated in both genitourinary and gastrointestinal sources and exhibited a wider range of phenotypes, particularly in the ability to ferment mannitol and/or raffinose.

The aims of this present study were (1) to assess the antimicrobial effect of ozone from a novel ozone–generating device (Heolozone, USA) [0.052% (v/v) in air delivered at a rate of 13.33 ml·s^–1] on primary root carious lesions (PRCLs) and (2) to evaluate the efficacy of ozone specifically on Streptococcus mutans and Streptococcus sobrinus. In study 1, 40 soft PRCLs from freshly extracted teeth were randomly divided into two groups to test the antimicrobial effect on PRCLs from exposure to ozonated water for either 10 or 20 s. Half of a lesion was removed using a sterile excavator. Subsequently, the remaining lesion was exposed to the ozonised water for a period of either 10 or 20 s (corresponding to 0.069 or 0.138 ml of ozone, respectively). Using paired Student t tests, a significant (p<0.001) reduction (mean ± SE) was observed in the ozone–treated groups with either a 10–second (log₁₀ 3.57±0.37) or 20–second (log₁₀ 3.77±0.42) ozone application compared with the control groups (log₁₀ 5.91±0.15 and log₁₀ 6.18±0.21, respectively). In study 2, 40 sterile saliva–coated glass beads were randomly divided into two groups for each micro–organism. One glass bead was put into each bijou bottle with 3 ml of Todd–Hewitt broth. S. mutans and S. sobrinus were inoculated anaerobically overnight. Each glass bead was then washed with 2 ml of phosphate–buffered saline. Immediately, 10 s of ozone gas was applied to each glass bead in the test groups. There was a significant (p<0.0001) reduction (mean ± SE) in ozone–treated samples for S. mutans (log₁₀ 1.01±0.27) and S. sobrinus (log₁₀ 1.09±0.36) compared with the control samples (log₁₀ 3.93±0.07 and log₁₀ 4.61±0.13, respectively). This treatment regime is an effective, quick, conservative and simple method to kill micro–organisms in PRCLs. Ozone gas application for a period of 10 s was also capable of reducing the numbers of S. mutans and S. sobrinus on saliva–coated glass beads in vitro.

Penicillin-resistant strains of Streptococcus pneumoniae possess forms of penicillin-binding proteins (PBPs) that have a low affinity for penicillin compared to those from penicillin-sensitive strains. PBP genes from penicillin-resistant isolates are very variable and have a mosaic structure composed of blocks of nucleotides that are similar to those found in PBP genes from penicillin-sensitive isolates and blocks that differ by up to 21%. These chromosomally encoded mosaic genes have presumably arisen following transformation and homologous recombination with PBP genes from a number of closely related species. This study shows that PBP2B genes from many penicillin-resistant isolates of S. pneumoniae contain blocks of nucleotides originating from Streptococcus mitis. In several instances it would appear that this material alone is sufficient to produce a low affinity PBP2B. In other examples PBP2B genes possess blocks of nucleotides from S. mitis and at least one additional unidentified species. Mosaic structure was also found in the PBP2B genes of penicillin-sensitive isolates of S. mitis or S. pneumoniae. These mosaics did not confer penicillin resistance but nevertheless reveal something of the extent to which localized recombination occurs in these naturally transformable streptococci.