Delineation of Streptococcus dysgalactiae, Its Subspecies, and Its Clinical and Phylogenetic Relationship to Streptococcus pyogenes

Abstract

The taxonomic status and structure of Streptococcus dysgalactiae have been the object of much confusion. Bacteria belonging to this species are usually referred to as Lancefield group C or group G streptococci in clinical settings in spite of the fact that these terms lack precision and prevent recognition of the exact clinical relevance of these bacteria. The purpose of this study was to develop an improved basis for delineation and identification of the individual species of the pyogenic group of streptococci in the clinical microbiology laboratory, with a special focus on S. dysgalactiae. We critically reexamined the genetic relationships of the species S. dysgalactiae, Streptococcus pyogenes, Streptococcus canis, and Streptococcus equi, which may share Lancefield group antigens, by phylogenetic reconstruction based on multilocus sequence analysis (MLSA) and 16S rRNA gene sequences and by emm typing combined with phenotypic characterization. Analysis of concatenated sequences of seven genes previously used for examination of viridans streptococci distinguished robust and coherent clusters. S. dysgalactiae consists of two separate clusters consistent with the two recognized subspecies dysgalactiae and equisimilis. Both taxa share alleles with S. pyogenes in several housekeeping genes, which invalidates identification based on single-locus sequencing. S. dysgalactiae, S. canis, and S. pyogenes constitute a closely related branch within the genus Streptococcus indicative of recent descent from a common ancestor, while S. equi is highly divergent from other species of the pyogenic group streptococci. The results provide an improved basis for identification of clinically important pyogenic group streptococci and explain the overlapping spectrum of infections caused by the species associated with humans.

Novel Molecular Method for Identification of Streptococcus pneumoniae Applicable to Clinical Microbiology and 16S rRNA Sequence-Based Microbiome Studies

“…Frequent homologous recombination within and between Streptococcus species renders identification based on sequences of single loci problematic (5,14,15,17,18,23). With this background, it is remarkable that the cytosine at position 203 in the 16S rRNA gene of S. pneumoniae appears to be fully conserved in the population of S. pneumoniae while strains of all other mitis group streptococci have an adenosine at this position.…”

“…Multilocus sequence analysis (MLSA) eliminates the potential problems resulting from homologous recombination and has been applied with success in the identification of several bacterial species that are difficult to differentiate by simpler methods (5,13,17,18,23,29,25,33). Schemes based on four to seven gene loci have proven valuable in differentiation of Streptococcus species (5,17,18). Specifically, an MLSA-based procedure for identification of S. pneu-moniae was reported by Hanage et al (16).…”

“…As a result of improved sequencing technologies, identification based on sequence comparisons of multiple housekeeping genes has become technically and economically feasible. Multilocus sequence analysis (MLSA) eliminates the potential problems resulting from homologous recombination and has been applied with success in the identification of several bacterial species that are difficult to differentiate by simpler methods (5,13,17,18,23,29,25,33). Schemes based on four to seven gene loci have proven valuable in differentiation of Streptococcus species (5, 17, 18).…”

Identification of Gram-Positive Cocci by Use of Matrix-Assisted Laser Desorption Ionization–Time of Flight Mass Spectrometry: Comparison of Different Preparation Methods and Implementation of a Practical Algorithm for Routine Diagnostics

“…Members of the S. mitis group, including S. pneumoniae, are closely related, and even the discriminatory power of the 16S rRNA gene is too low for reliable differentiation (2). However, due to clinical reasons, the differentiation of S. pneumoniae is of critical importance, and additional tests are required in case of a MALDI-TOF MS S. pneumoniae identification, (24). Nevertheless, differentiation of these two species is required in the clinical environment.…”

Adult Invasive and Noninvasive Infections Due to Streptococcus dysgalactiae subsp. equisimilis in France from 2006 to 2010

“…Most previous studies have characterized strains only from invasive infections. However, three studies compared invasive and noninvasive infections, and these studies found a correlation between emm type and invasive disease potential (3,27,31). In these studies, stG6, stG10, stG480, stG485, stG2078, and stG6792 were described as invasive emm types.…”