Accuracy of phenotypic and genotypic testing for identification of Streptococcus pneumoniae and description of Streptococcus pseudopneumoniae sp. nov

Abstract

We have identified an unusual group of viridans group streptococci that resemble Streptococcus pneumoniae. DNA-DNA homology studies suggested that a subset of these isolates represent a novel species that may be included in the S. oralis-S. mitis group of viridans group streptococci. We suggest that this novel species be termed Streptococcus pseudopneumoniae. A combination of phenotypic and genetic reactions allows its identification. S. pseudopneumoniae strains do not have pneumococcal capsules, are resistant to optochin (inhibition zones, less than 14 mm) when they are incubated under an atmosphere of increased CO2 but are susceptible to optochin (inhibition zones, >14 mm) when they are incubated in ambient atmospheres, are not soluble in bile, and are positive by the GenProbe AccuProbe Pneumococcus test. The bile solubility test is more specific than the optochin test for identification of S. pneumoniae. Genetic tests for pneumolysin (ply) and manganese-dependent superoxide dismutase (sodA) and identification tests with a commercial probe, AccuProbe Pneumococcus, do not discriminate between the new species and S. pneumoniae.

FIG. 1.

Phylogenetic tree, based on comparative analysis of the sodA gene sequences, showing the relationship of S. pseudopneumoniae sp. nov. and related species of the genus Streptococcus.

FIG. 2.

Phylogenetic tree, based on comparative analysis of the 16S rDNA sequences, showing the relationship of S. pseudopneumoniae sp. nov. and related species of the Smit group. The limit criterion used to show the bootstrap numbers was above 85%, and S. pyogenes was used as the outgroup.