Pathogenicity Factors in Group C and G Streptococci

Integrative genomic, virulence, and transcriptomic analysis of emergent Streptococcus dysgalactiae subspecies equisimilis (SDSE) emm type stG62647 isolates causing human infections

Streptococcus dysgalactiae subspecies equisimilis (SDSE) is a Gram-positive bacterial pathogen that infects humans and is closely related to group A streptococcus (GAS). Compared with GAS, far less is known about SDSE pathobiology. Increased rates of invasive SDSE infections have recently been reported in many countries. One SDSE emm type (stG62647) is known to cause severe diseases, including necrotizing soft-tissue infections, endocarditis, and osteoarticular infections. To increase our understanding of the molecular pathogenesis of stG62647 SDSE isolates causing human infections, we sequenced to closure the genomes of 120 stG62647 SDSE isolates. The genomes varied in size from 2.1 to 2.24 Mb pairs. The great majority of stG62647 isolates had IS1548 integrated into the silB gene, thereby inactivating it. Regions of difference, such as mobile genetic elements, were the largest source of genomic diversity. All 120 stG62647 isolates were assayed for virulence using a well-established mouse model of necrotizing myositis. An unexpectedly wide range of virulence was identified (20% to 95%), as assessed by near-mortality data. To explore the molecular mechanisms underlying virulence differences, we analyzed RNAseq transcriptome profiles for 38 stG62647 isolates (comprising the 19 least and most virulent) grown in vitro. Genetic polymorphisms were identified from whole-genome sequence data. Collectively, the results suggest that these SDSE isolates use multiple genetic pathways to alter virulence phenotype. The data also suggest that human genetics and underlying medical conditions contribute to disease severity. Our study integrates genomic, mouse virulence, and RNAseq data to advance our understanding of SDSE pathobiology and its molecular pathogenesis.

IMPORTANCE

This study integrated genomic sequencing, mouse virulence assays, and bacterial transcriptomic analysis to advance our understanding of the molecular mechanisms contributing to Streptococcus dysgalactiae subsp. equisimilis emm type stG62647 pathogenesis. We tested a large cohort of genetically closely related stG62647 isolates for virulence using an established mouse model of necrotizing myositis and discovered a broad spectrum of virulence phenotypes, with near-mortality rates ranging from 20% to 95%. This variation was unexpected, given their close genetic proximity. Transcriptome analysis of stG62647 isolates responsible for the lowest and highest near-mortality rates suggested that these isolates used multiple molecular pathways to alter their virulence. In addition, some genes encoding transcriptional regulators and putative virulence factors likely contribute to SDSE emm type stG62647 pathogenesis. These data underscore the complexity of pathogen-host interactions in an emerging SDSE clonal group.

The 1.7 Å crystal structure of the C5a peptidase from Streptococcus agalactiae (ScpB) reveals an active site competent for catalysis

A 1.7 Å structure is presented for an active form of the virulence factor ScpB, the C5a peptidase from Streptococcus agalactiae. The previously reported structure of the ScpB active site mutant exhibited a large separation (~20 Å) between the catalytic His and Ser residues. Significant differences are observed in the catalytic domain between the current and mutant ScpB structures resulting with a high RMSDCα (4.6 Å). The fold of the active form of ScpB is nearly identical to ScpA (RMSDCα 0.2 Å), the C5a-peptidase from Streptococcus pyogenes. Both ScpA and ScpB have comparable activity against human C5a, indicating neither enzyme require host proteins for C5a-ase activity. These studies are a first step in resolving reported differences in the specificities of these enzymes.

Invasive beta-haemolytic streptococcal infections, Finland, 2006 to 2020: increase in Lancefield group C/G infections

BackgroundInvasive infections with beta-haemolytic streptococci of Lancefield groups A (iGAS), B (iGBS) and C/G (iGCGS) are a major cause of morbidity and mortality worldwide.AimWe studied incidence trends of invasive beta-haemolytic streptococcal infections in Finland, focusing on iGCGS.MethodsWe conducted a retrospective register-based study. Cases were defined as isolations from blood and/or cerebrospinal fluid and retrieved from the National Infectious Disease Register where all invasive cases are mandatorily notified.ResultsBetween 2006 and 2020, the mean annual incidence was 4.1 per 100,000 for iGAS (range: 2.1-6.7), 5.2 for iGBS (4.0-6.3) and 10.1 for iGCGS (5.4-17.6). The incidence displayed an increasing trend for all groups, albeit for iGBS only for individuals 45 years and older. The increase was particularly sharp for iGCGS (8% annual relative increase). The incidence rate was higher in males for iGCGS (adjusted incidence rate ratio (IRR) = 1.6; 95% confidence interval (CI): 1.5-1.8) and iGAS (adjusted IRR = 1.3; 95% CI: 1.1-1.4); for iGBS, the association with sex was age-dependent. In adults, iGCGS incidence increased significantly with age. Recurrency was seen for iGCGS and secondarily iGBS, but not for iGAS. Infections with iGCGS and iGBS peaked in July and August.ConclusionsThe incidence of invasive beta-haemolytic streptococcal infections in Finland has been rising since 2006, especially for iGCGS and among the elderly population. However, national surveillance still focuses on iGAS and iGBS, and European Union-wide surveillance is lacking. We recommend that surveillance of iGCGS be enhanced, including systematic collection and typing of isolates, to guide infection prevention strategies.

Phenotypic and Genotypic Characterization of Antimicrobial Resistance in Streptococci Isolated from Human and Animal Clinical Specimens

Recently, the phenomenon of infection of humans as hosts by animal pathogens has been increasing. Streptococcus is an example of a genus in which bacteria overcome the species barrier. Therefore, monitoring infections caused by new species of human pathogens is critical to their spread. Seventy-five isolates belonging to streptococcal species that have recently been reported as a cause of human infections with varying frequency, were tested. The aim of the study was to determine the drug resistance profiles of the tested strains, the occurrence of resistance genes and genes encoding the most important streptococcal virulence factors. All tested isolates retained sensitivity to β-lactam antibiotics. Resistance to tetracyclines occurred in 56% of the tested strains. We have detected the MLS_B type resistance (cross-resistance to macrolide, lincosamide, and streptogramin B) in 20% of the tested strains. 99% of the strains had tetracycline resistance genes. The erm class genes encoding MLS_B resistance were present in 47% of strains. Among the strains with MLS_B resistance, 92% had the streptokinase gene, 58% the streptolysin O gene and 33% the streptolysin S gene. The most extensive resistance concerned isolates that accumulated the most traits and genes, both resistance genes and virulence genes, increasing their pathogenic potential. Among the tested strains, the gene encoding streptokinase was the most common. The results of the prove that bacteria of the species S. uberis, S. dysgalactiae and S. gallolyticus are characterized by a high pathogenic potential and can pose a significant threat in case of infection of the human body.

Recurrent group G Streptococcus bacteremia: A case report and literature review

Streptococci group G is an important opportunistic pathogen and causes a wide variety of infections, including pharyngitis, skin and soft tissue infections, bacteremia, endocarditis, septic arthritis, intra-abdominal infections, meningitis, and streptococcal toxic shock-like syndrome. As a result, we discuss an interesting case of recurrent group G streptococcal bacteremia in a 68-year-old man presenting with altered mental status. We also discuss the risk factors, etiology, pathophysiology, diagnosis, and treatment of group G streptococcal bacteremia.

The Role of Streptococcal Cell-Envelope Proteases in Bacterial Evasion of the Innate Immune System

Bacteria possess the ability to evolve varied and ingenious strategies to outwit the host immune system, instigating an evolutionary arms race. Proteases are amongst the many weapons employed by bacteria, which specifically cleave and neutralize key signalling molecules required for a coordinated immune response. In this article, we focus on a family of S8 subtilisin-like serine proteases expressed as cell-envelope proteases (CEPs) by group A and group B streptococci. Two of these proteases known as Streptococcus pyogenes CEP (SpyCEP) and C5a peptidase cleave the chemokine CXCL8 and the complement fragment C5a, respectively. Both CXCL8 and C5a are potent neutrophil-recruiting chemokines, and by neutralizing their activity, streptococci evade a key defence mechanism of innate immunity. We review the mechanisms by which CXCL8 and C5a recruit neutrophils and the characterization of SpyCEP and C5a peptidase, including both in vitro and in vivo studies. Recently described structural insights into the function of this CEP family are also discussed. We conclude by examining the progress of prototypic vaccines incorporating SpyCEP and C5a peptidase in their preparation. Since streptococci-producing SpyCEP and C5a peptidase are responsible for a considerable global disease burden, targeting these proteases by vaccination strategies or by small-molecule antagonists should provide protection from and promote the resolution of streptococcal infections.

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.