Exploring the arthritogenicity of Streptococcus dysgalactiae subspecies equisimilis

Oddvar Oppegaard,Steinar Skrede,Bård Reiakvam Kittang,Haima Mylvaganam

doi:10.1186/s12866-018-1160-5

Abstract

BackgroundDuring the past decades, Streptococcus dysgalactiae subspecies equisimilis (SDSE) has been increasingly recognized as an important human pathogen. Osteoarticular infections is one of the predominant disease manifestations of SDSE, but the pathogenetic rationale for its arthritogenicity has yet to be unravelled. We aimed to explore if the rising incidence of osteoarticular infections caused by this pathogen in our region emanated from clonal expansion of strains with enhanced tropism for bone and joint tissue components or orthopaedic implants.ResultsTwenty-nine SDSE-isolates associated with osteoarticular infections were retrospectively identified. Their genomic content and affinity for fibronectin, collagen and stainless steel were compared to 24 temporally and geographically matched SDSE blood culture isolates obtained from patients without bone or joint infections.Despite a thorough genetic and phenotypic dissection, neither the presence or absence of any single gene, nor the binding abilities of the SDSE isolates, were predictive of clinical entity. SNP analysis revealed a heterogenous population, and a correlation between phylogenetic relationships and disease manifestation was not evident. However, we identified a strong concordance between phenotypic binding abilities and genetic variations in the pilus-region, also denoted as the FCT-region (Fibronectin binding, Collagen binding and T-antigen). This observation could be related to the ample and varied repertoire of putative adhesins residing within this region, including proteins predicted to adhere to fibronectin and collagen, as well as fibrinogen.ConclusionsSDSE strains associated with osteoarticular infections do not emanate from subpopulation characterized by distinct genetic or phenotypic traits. The genetic architecture of the pilus region was predictive of the adhesive properties of the SDSE-isolates, but its role in tissue tropism needs further investigation. To the best of our knowledge, this is the first comprehensive characterization of the genetic landscape of the SDSE pilus region.

Highlights

During the past decades, Streptococcus dysgalactiae subspecies equisimilis (SDSE) has been increasingly recognized as an important human pathogen
Patients with a recent history of septic arthritis or osteomyelitis caused by S. pyogenes had increased anti-Cpa-titers, suggesting a role for this virulence factor in the pathogenesis of Osteoarticular infection (OAI) [15]
From a total of 42 clinical OAI cases, 29 bacterial isolates were available for analysis; 16 were obtained from blood cultures and 13 detected in synovial fluid or tissue specimens

Summary

Introduction

Streptococcus dysgalactiae subspecies equisimilis (SDSE) has been increasingly recognized as an important human pathogen. Cpa is part of the pilus-apparatus in S. pyogenes, encoded by the FCT-region (Fibronectin binding, Collagen binding and T-antigen). This region displays a substantial genetic heterogeneity, and nine different FCT-variants have been characterized [16]. In a recent effort to delineate S. pyogenes strains according to their tropism for skin or throat, the FCT-region and the emm-region were identified as two of the most likely determinants [17]. Homologues of both these regions are present in SDSE, and a correlation to their propensity for OAIs is conceivable

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