Exploring the arthritogenicity of Streptococcus dysgalactiae subspecies equisimilis

Streptococcus dysgalactiae subsp. equisimilis infection and its intersection with Streptococcus pyogenes

SUMMARYStreptococcus dysgalactiae subsp. equisimilis (SDSE) is an increasingly recognized cause of disease in humans. Disease manifestations range from non-invasive superficial skin and soft tissue infections to life-threatening streptococcal toxic shock syndrome and necrotizing fasciitis. Invasive disease is usually associated with co-morbidities, immunosuppression, and advancing age. The crude incidence of invasive disease approaches that of the closely related pathogen, Streptococcus pyogenes. Genomic epidemiology using whole-genome sequencing has revealed important insights into global SDSE population dynamics including emerging lineages and spread of anti-microbial resistance. It has also complemented observations of overlapping pathobiology between SDSE and S. pyogenes, including shared virulence factors and mobile gene content, potentially underlying shared pathogen phenotypes. This review provides an overview of the clinical and genomic epidemiology, disease manifestations, treatment, and virulence determinants of human infections with SDSE with a particular focus on its overlap with S. pyogenes. In doing so, we highlight the importance of understanding the overlap of SDSE and S. pyogenes to inform surveillance and disease control strategies.

Inter-species gene flow drives ongoing evolution of Streptococcus pyogenes and Streptococcus dysgalactiae subsp. equisimilis

Streptococcus dysgalactiae subsp. equisimilis (SDSE) is an emerging cause of human infection with invasive disease incidence and clinical manifestations comparable to the closely related species, Streptococcus pyogenes. Through systematic genomic analyses of 501 disseminated SDSE strains, we demonstrate extensive overlap between the genomes of SDSE and S. pyogenes. More than 75% of core genes are shared between the two species with one third demonstrating evidence of cross-species recombination. Twenty-five percent of mobile genetic element (MGE) clusters and 16 of 55 SDSE MGE insertion regions were shared across species. Assessing potential cross-protection from leading S. pyogenes vaccine candidates on SDSE, 12/34 preclinical vaccine antigen genes were shown to be present in >99% of isolates of both species. Relevant to possible vaccine evasion, six vaccine candidate genes demonstrated evidence of inter-species recombination. These findings demonstrate previously unappreciated levels of genomic overlap between these closely related pathogens with implications for streptococcal pathobiology, disease surveillance and prevention.

Analysis of the Genomics and Mouse Virulence of an Emergent Clone of Streptococcus dysgalactiae Subspecies equisimilis

Streptococcus dysgalactiae subsp. equisimilis is a bacterial pathogen that is increasingly recognized as a cause of severe human infections. Much less is known about the genomics and infection pathogenesis of S. dysgalactiae subsp. equisimilis strains compared to the closely related bacterium Streptococcus pyogenes. To address these knowledge deficits, we sequenced to closure the genomes of seven S. dysgalactiae subsp. equisimilis human isolates, including six that were emm type stG62647. Recently, for unknown reasons, strains of this emm type have emerged and caused an increasing number of severe human infections in several countries. The genomes of these seven strains vary between 2.15 and 2.21 Mbp. The core chromosomes of these six S. dysgalactiae subsp. equisimilis stG62647 strains are closely related, differing on average by only 495 single-nucleotide polymorphisms, consistent with a recent descent from a common progenitor. The largest source of genetic diversity among these seven isolates is differences in putative mobile genetic elements, both chromosomal and extrachromosomal. Consistent with the epidemiological observations of increased frequency and severity of infections, both stG62647 strains studied were significantly more virulent than a strain of emm type stC74a in a mouse model of necrotizing myositis, as assessed by bacterial CFU burden, lesion size, and survival curves. Taken together, our genomic and pathogenesis data show the strains of emm type stG62647 we studied are closely genetically related and have enhanced virulence in a mouse model of severe invasive disease. Our findings underscore the need for expanded study of the genomics and molecular pathogenesis of S. dysgalactiae subsp. equisimilis strains causing human infections. IMPORTANCE Our studies addressed a critical knowledge gap in understanding the genomics and virulence of the bacterial pathogen Streptococcus dysgalactiae subsp. equisimilis. S. dysgalactiae subsp. equisimilis strains are responsible for a recent increase in severe human infections in some countries. We determined that certain S. dysgalactiae subsp. equisimilis strains are genetically descended from a common ancestor and that these strains can cause severe infections in a mouse model of necrotizing myositis. Our findings highlight the need for expanded studies on the genomics and pathogenic mechanisms of this understudied subspecies of the Streptococcus family.

Comparison of an automated DNA extraction and 16S rDNA real time PCR/sequencing diagnostic method using optimized reagents with culture during a 15-month study using specimens from sterile body sites

Background

16S rDNA-PCR for the identification of a bacterial species is an established method. However, the DNA extraction reagents as well as the PCR reagents may contain residual bacterial DNA, which consequently generates false-positive PCR results. Additionally, previously used methods are frequently time-consuming. Here, we describe the results obtained with a new technology that uses DNA-free reagents for automated DNA extraction and subsequent real time PCR using sterile clinical specimens.

Results

In total, we compared 803 clinical specimens using real time PCR and culturing. The clinical specimens were mainly of orthopedic origin received at our diagnostic laboratory. In 595 (74.1%) samples, the results were concordant negative, and in 102 (12.7%) the results were concordant positive. A total of 170 (21.2%) clinical specimens were PCR-positive, of which 62 (36.5% from PCR positive, 7.7% in total) gave an additional benefit to the patient since only the PCR result was positive. Many of these 62 positive specimens were strongly positive based on crossingpoint values (54% < Cp 30), and these 62 positive clinical specimens were diagnosed as medically relevant as well. Thirty-eight (4.2%) clinical specimens were culture-positive (25 of them were only enrichment culture positive) but PCR-negative, mainly for S. epidermidis, S. aureus and C. acnes. The turnaround times for negative specimens were 4 hours (automated DNA extraction and real time PCR) and 1 working day for positive specimens (including Sanger sequencing). Melting-curve analysis of SYBR Green-PCR enables the differentiation of specific and unspecific PCR products. Using Ripseq, even mixed infections of 2 bacterial species could be resolved.

Conclusions

For endocarditis cases, the added benefit of PCR is obvious. The crucial innovations of the technology enable timely reporting of explicit reliable results for adequate treatment of patients. Clinical specimens with truly PCR-positive but culture-negative results represent an additional benefit for patients. Very few results at the detection limit still have to be critically examined.

Pathogenicity and drug resistance of animal streptococci responsible for human infections

Bacteria of the genus Streptococcus, earlier considered typically animal, currently have also been causing infections in humans. It is necessary to make clinicians aware of the emergence of new species that may cause the development of human diseases. There is an increasing frequency of isolation of streptococci such as S. suis, S. dysgalactiae, S. iniae and S. equi from people. Isolation of Streptococcus bovis/Streptococcus equinus complex bacteria has also been reported. The streptococcal species described in this review are gaining new properties and virulence factors by which they can thrive in new environments. It shows the potential of these bacteria to changes in the genome and the settlement of new hosts. Information is presented on clinical cases that concern streptococcus species belonging to the groups Bovis, Pyogenic and Suis. We also present the antibiotic resistance profiles of these bacteria. The emerging resistance to β-lactams has been reported. In this review, the classification, clinical characteristics and antibiotic resistance of groups and species of streptococci considered as animal pathogens are summarized.

Singularities of Pyogenic Streptococcal Biofilms - From Formation to Health Implication

Biofilms are generally defined as communities of cells involved in a self-produced extracellular matrix adhered to a surface. In biofilms, the bacteria are less sensitive to host defense mechanisms and antimicrobial agents, due to multiple strategies, that involve modulation of gene expression, controlled metabolic rate, intercellular communication, composition, and 3D architecture of the extracellular matrix. These factors play a key role in streptococci pathogenesis, contributing to therapy failure and promoting persistent infections. The species of the pyogenic group together with Streptococcus pneumoniae are the major pathogens belonging the genus Streptococcus, and its biofilm growth has been investigated, but insights in the genetic origin of biofilm formation are limited. This review summarizes pyogenic streptococci biofilms with details on constitution, formation, and virulence factors associated with formation.

Septic arthritis due to streptococci and enterococci in native joints: a 13 year retrospective study

OBJECTIVES

Streptococcal species are the second most common cause of native joint septic arthritis (SA). However, there are few systematic data about streptococcal SA.

METHODS

The medical records of adults with SA caused by streptococci, pneumococci, and enterococci at our tertiary care centre between 2003 and 2015 were reviewed.

RESULTS

71 patients (34% female) with 83 affected joints were included. Median age was 62 years. A single joint was involved in 62 patients (87%). One or more comorbidities were present in 58 patients (82%). 16 patients (23%) had a concomitant soft-tissue infection overlying the affected joint. The hematogenous route was the dominating pathogenesis (42/71, 59%). 9 (13%) patients were diagnosed with endocarditis. The knee was the most commonly affected joint (27/83, 33%) followed by shoulder (13/83, 16%). ß-haemolytic streptococci were most commonly identified (37/71, 52%) followed by polymicrobial infections (12/71, 17%). Surgical interventions included arthroscopic irrigation and debridement in 31 (44%), arthrotomy in 23 (32%), and amputation in five patients (7%). Median duration of antimicrobial therapy was 42 days. Antibiotic treatment without any surgical intervention was performed in 5 (7%) patients. Outcome was good in 55 (89%) patients; mortality was 13% with four of nine deaths attributed to joint infection. Age and pathogen group independently predicted poor outcome in recursive partitioning analysis.

CONCLUSIONS

Streptococcal SA was mostly due to ß-haemolytic streptococci in older and polymorbid patients. Old age, anginosus group streptococci, enterococci, and polymicrobial infections predicted poor outcome, while antibiotic treatment duration can likely be shortened.