Comparative Genomic Analyses of <i>Streptococcus pseudopneumoniae</i> Provide Insight into Virulence and Commensalism Dynamics

<div><p><i>Streptococcus pseudopneumoniae</i> (SPPN) is a recently described species of the viridans group streptococci (VGS). Although the pathogenic potential of <i>S. pseudopneumoniae</i> remains uncertain, it is most commonly isolated from patients with underlying medical conditions, such as chronic obstructive pulmonary disease. <i>S. pseudopneumoniae</i> can be distinguished from the closely related species, <i>S. pneumoniae</i> and <i>S. mitis</i>, by phenotypic characteristics, including optochin resistance in the presence of 5% CO₂, bile insolubility, and the lack of the pneumococcal capsule. Previously, we reported the draft genome sequence of <i>S. pseudopneumoniae</i> IS7493, a clinical isolate obtained from an immunocompromised patient with documented pneumonia. Here, we use comparative genomics approaches to identify similarities and key differences between <i>S. pseudopneumoniae</i> IS7493, <i>S. pneumoniae</i> and <i>S. mitis</i>. The genome structure of <i>S. pseudopneumoniae</i> IS7493 is most closely related to that of <i>S. pneumoniae</i> R6, but several recombination events are evident. Analysis of gene content reveals numerous unique features that distinguish <i>S. pseudopneumoniae</i> from other streptococci. The presence of loci for competence, iron transport, pneumolysin production and antimicrobial resistance reinforce the phylogenetic position of <i>S. pseudopneumoniae</i> as an intermediate species between <i>S. pneumoniae</i> and <i>S. mitis</i>. Additionally, the presence of several virulence factors and antibiotic resistance mechanisms suggest the potential of this commensal species to become pathogenic or to contribute to increasing antibiotic resistance levels seen among the VGS.</p>