Streptococcus pseudopneumoniae

Streptococcus pseudopneumoniae is a novel species belonging to the viridans group streptococci (VGS). Accurate species identification is challenging due to significant homology to other VGS. Whole-genome sequencing of S. pseudopneumoniae suggests it most likely originated from Streptococcus pneumoniae, sharing many of its virulence genes. There are several limitations when using traditional phenotypic identification methods to identify this organism. Other identification approaches include genotypic methods, pherotype analysis, and matrix-assisted laser desorption ionization–time of flight mass spectrometry. S. pseudopneumoniae is most commonly isolated from respiratory specimens, and its associations with chronic obstructive pulmonary disease and aspiration pneumonia have been previously described, suggesting that the organism treads the fine line between commensal and pathogen. Recent isolation of S. pseudopneumoniae from blood raises the important question of its clinical relevance. Antimicrobial susceptibility profiles of S. pseudopneumoniae indicate a higher level of resistance than other VGS. However, further information may be required to determine the choice of breakpoints.