Analysis of a viridans group strain reveals a case of bacteremia due to lancefield group G alpha-hemolytic Streptococcus dysgalactiae subsp equisimilis in a patient with pyomyositis and reactive arthritis

Abstract

Streptococcus dysgalactiae is classified by a combination of phenotypic and genotypic characteristics into Lancefield group C alpha-hemolytic Streptococcus dysgalactiae subsp. dysgalactiae and Lancefield group C, group G, and group L beta-hemolytic Streptococcus dysgalactiae subsp. equisimilis. In this study, we report the isolation of a catalase-negative, alpha-hemolytic, optochin- and bacitracin-resistant viridans group strain, which does not grow in 10 or 40% bile, on MacConkey agar or bile esculin agar, or in 6% NaCl, from the blood culture of a 73-year-old woman with pyomyositis and poststreptococcal reactive arthritis. Lancefield grouping revealed that the strain was a group G streptococcus. The Vitek system (GPI) showed that it was unidentified, and the API system (20 STREP) showed that it was 95.7% S. dysgalactiae subsp. dysgalactiae. 16S rRNA gene sequencing showed that it was a strain of S. dysgalactiae. Based on phylogenetic affiliation with 16S rRNA gene or GroEL amino acid (another bacterial gene, in addition to 16S rRNA gene, that is highly conserved) sequences, the strain is most closely related to Lancefield group C beta-hemolytic S. dysgalactiae subsp. equisimilis. PCR amplification and sequencing of the streptolysin S structural gene (sagA) and M protein gene (emm) hypervariable region showed the presence of these suspected primary virulence factors. Further studies would delineate whether the isolate is just a hemolysin-deficient variant of group G beta-hemolytic S. dysgalactiae subsp. equisimilis or a novel type of S. dysgalactiae. The present case showed that group G alpha-hemolytic S. dysgalactiae subsp. equisimilis can be associated with serious invasive infection and poststreptococcal sequelae.

FIG. 1.

Coronal (A) and axial (B) T1- and T2-weighted magnetic resonance imaging of the pelvis showing a multiloculated abscess (arrows) in the subcutaneous area of the right buttock.

FIG. 2.

Phylogenetic tree showing the relationships of Lancefield group G alpha-hemolytic S. dysgalactiae subsp. equisimilis to other types of S. dysgalactiae and other streptococci. The tree was inferred from 16S rRNA data by the neighbor-joining method, and bootstrap values were calculated from 1,000 trees. The scale bar indicates the estimated number of substitutions per 100 bases with the Jukes-Cantor correction. Names and accession numbers (in parentheses) are given as cited in the GenBank database.