Interactions Between Streptococcus gordonii and Fusobacterium nucleatum Altered Bacterial Transcriptional Profiling and Attenuated the Immune Responses of Macrophages

Interspecies coaggregation promotes transcriptional changes in oral bacteria, affecting bacterial pathogenicity. Streptococcus gordonii (S. gordonii) and Fusobacterium nucleatum (F. nucleatum) are common oral inhabitants. The present study investigated the transcriptional profiling of S. gordonii and F. nucleatum subsp. polymorphum in response to the dual-species coaggregation using RNA-seq. Macrophages were infected with both species to explore the influence of bacterial coaggregation on both species’ abilities to survive within macrophages and induce inflammatory responses. Results indicated that, after the 30-min dual-species coaggregation, 116 genes were significantly up-regulated, and 151 genes were significantly down-regulated in S. gordonii; 97 genes were significantly down-regulated, and 114 genes were significantly up-regulated in F. nucleatum subsp. polymorphum. Multiple S. gordonii genes were involved in the biosynthesis and export of cell-wall proteins and carbohydrate metabolism. F. nucleatum subsp. polymorphum genes were mostly associated with translation and protein export. The coaggregation led to decreased expression levels of genes associated with lipopolysaccharide and peptidoglycan biosynthesis. Coaggregation between S. gordonii and F. nucleatum subsp. polymorphum significantly promoted both species’ intracellular survival within macrophages and attenuated the production of pro-inflammatory cytokines IL-6 and IL-1β. Physical interactions between these two species promoted a symbiotic lifestyle and repressed macrophage’s killing and pro-inflammatory responses.

Streptococcus gordonii DL1 evades polymorphonuclear leukocyte-mediated killing via resistance to lysozyme

Streptococcus gordonii is an etiological bacterial agent of infective endocarditis. Although the pathogenesis mechanisms are not well understood, the interaction between streptococci and phagocytes is considered important for the development of infective endocarditis. Previous studies show that some S. gordonii strains, including DL1, survive in polymorphonuclear leukocytes (PMNs), whereas other strains such as SK12 are sensitive to PMN-dependent killing. In this study, we assessed the differences between the sensitivity of S. gordonii DL1 and S. gordonii SK12 to PMN-dependent killing. S. gordonii DL1 showed a higher survival when treated with PMNs than SK12. Both S. gordonii DL1 and S. gordonii SK12 showed high resistance to low pH condition. Compared to S. gordonii SK12, S. gordonii DL1 was sensitive to hydrogen peroxide. However, the resistance of S. gordonii DL1 to the tested bactericidal agents, especially lysozyme, was higher than that of SK12. Furthermore, we performed a bactericidal assay by treating a mixture of S. gordonii DL1 and SK12 with PMNs. S. gordonii DL1 did not enhance the survival of S. gordonii SK12 exposed to PMNs. These results indicated that S. gordonii DL1 is resistant to bactericidal agents that degrade bacteria in phagolysosomes. In addition, there was no secretory factor involved in the resistance to bactericidal agents. The findings of this study may help develop treatments for infective endocarditis caused by S. gordonii.

A Challenge of COVID—19: Associated Infective Endocarditis with Streptococcus gordonii in a Young Immunocompetent Patient

The COVID-19 pandemic is a new challenge for the diagnosis and treatment of infective endocarditis (IE). Fever and other unspecific symptoms of coronaviral infection could be misleading or masking its manifestations. We present the case of a young patient admitted for persistent fever, profuse sweating, headache, articular pain, myalgias, and weight loss. She reported regression taste and smell disorders compared to a month earlier when diagnosed with moderate COVID-19 pneumonia. While the RT-PCR SARS-COV-2 test was positive, she was admitted to a COVID-19 ward. Investigations of febrile syndrome revealed two positive blood cultures with Streptococcus gordonii and the presence of vegetations on the aortic valve, supporting a certain diagnosis of IE. After six weeks of antibiotic treatment, the patient had clinical and biologic favorable outcomes. Streptococcus gordonii is a common commensal related to the dental biofilm, although there were no caries in our patient. The influence of COVID-19 infection on the human microbiome by modifying the virulence of some commensal germs may be a risk factor for IE pathogenesis on native valves and requires the vigilance of clinicians for suspicion of this disease.

Novel Virulent Bacteriophage SG005, Which Infects Streptococcus gordonii, Forms a Distinct Clade among Streptococcus Viruses

Bacteriophages are viruses that specifically infect bacteria and are classified as either virulent phages or temperate phages. Despite virulent phages being promising antimicrobial agents due to their bactericidal effects, the implementation of phage therapy depends on the availability of virulent phages against target bacteria. Notably, virulent phages of Streptococcus gordonii, which resides in the oral cavity and is an opportunistic pathogen that can cause periodontitis and endocarditis have previously never been found. We thus attempted to isolate virulent phages against S. gordonii. In the present study, we report for the first time a virulent bacteriophage against S. gordonii, <phi>SG005, discovered from drainage water. <phi>SG005 is composed of a short, non-contractile tail and a long head, revealing Podoviridae characteristics via electron microscopic analysis. In turbidity reduction assays, <phi>SG005 showed efficient bactericidal effects on S. gordonii. Whole-genome sequencing showed that the virus has a DNA genome of 16,127 bp with 21 coding sequences. We identified no prophage-related elements such as integrase in the <phi>SG005 genome, demonstrating that the virus is a virulent phage. Phylogenetic analysis indicated that <phi>SG005 forms a distinct clade among the streptococcus viruses and is positioned next to streptococcus virus C1. Molecular characterization revealed the presence of an anti-CRISPR (Acr) IIA5-like protein in the <phi>SG005 genome. These findings facilitate our understanding of streptococcus viruses and advance the development of phage therapy against S. gordonii infection.

Transcriptomic Responses to Coaggregation between Streptococcus gordonii and Streptococcus oralis

Cell-cell adhesion between oral bacteria plays a key role in the development of polymicrobial communities such as dental plaque. Oral streptococci such as Streptococcus gordonii and Streptococcus oralis are important early colonizers of dental plaque and bind to a wide range of different oral microorganisms, forming multispecies clumps or ‘coaggregates’. S. gordonii actively responds to coaggregation by regulating gene expression. To further understand these responses, we assessed gene regulation in S. gordonii and S. oralis following coaggregation in 25% human saliva. Coaggregates were formed by mixing and, after 30 minutes, RNA was extracted for Dual RNASeq analysis. In S. oralis , 18 genes (6 upregulated and 12 downregulated) were regulated by coaggregation. Significantly downregulated genes encoded functions such as amino acid and antibiotic biosynthesis, ribosome and central carbon metabolism. In total, 28 genes were differentially regulated in Streptococcus gordonii (25 upregulated and 3 downregulated). Many genes associated with transporters and a two component (NisK/SpaK) regulatory system were upregulated following coaggregation. Our comparative analyses of S. gordonii - S. oralis with different previously published S. gordonii pairings ( S. gordonii - Fusobacterium nucleatum and S. gordonii - Veillonella parvula ) suggest that the gene regulation is specific to each pairing and responses do not appear to be conserved. This ability to distinguish between neighboring bacteria may be important for S. gordonii to adapt appropriately during the development of complex biofilms such as dental plaque. Importance Dental plaque is responsible for two of the most prevalent diseases in humans, dental caries and periodontitis. Controlling the formation of dental plaque and preventing the transition from oral health to disease requires a detailed understanding of microbial colonization and biofilm development. Streptococci are among the most common colonizers of dental plaque. This study identifies key genes that are regulated when oral streptococci bind to one another, as they do in the early stages of dental plaque formation. We show that specific genes are regulated in two different oral streptococci following the formation of mixed-species aggregates. The specific responses of S. gordonii to coaggregation with S. oralis are different from coaggregation with other oral bacteria. Targeting the key genes that are upregulated during interspecies interactions may be a powerful approach to control the developing biofilm and maintain oral health.

Structural and functional analysis of the C-terminal region of Streptococcus gordonii SspB

Streptococcus gordonii is a member of the viridans streptococci and is an early colonizer of the tooth surface. Adherence to the tooth surface is enabled by proteins present on the S. gordonii cell surface, among which SspB belongs to one of the most well studied cell-wall-anchored adhesin families: the antigen I/II (AgI/II) family. The C-terminal region of SspB consists of three tandemly connected individual domains that display the DEv-IgG fold. These C-terminal domains contain a conserved Ca2+-binding site and isopeptide bonds, and they adhere to glycoprotein 340 (Gp340; also known as salivary agglutinin, SAG). Here, the structural and functional characterization of the C123 SspB domain at 2.7 Å resolution is reported. Although the individual C-terminal domains of Streptococcus mutans AgI/II and S. gordonii SspB show a high degree of both sequence and structural homology, superposition of these structures highlights substantial differences in their electrostatic surface plots, and this can be attributed to the relative orientation of the individual domains (C1, C2 and C3) with respect to each other and could reflect their specificity in binding to extracellular matrix molecules. Studies further confirmed that affinity for Gp340 or its scavenger receptor cysteine-rich (SRCR) domains requires two of the three domains of C123 SspB, namely C12 or C23, which is different from AgI/II. Using protein–protein docking studies, models for this observed functional difference between C123 SspB and C123 AgI/II in their binding to SRCR1 are presented.

Streptococcus gordonii septic arthritis of the glenohumeral joint following deltoid intramuscular vaccination

A 68-year-old woman presented for left shoulder pain, decreased range of motion (ROM) and fever 7 days following COVID-19 vaccination. Investigations showed a tender left deltoid mass, decreased shoulder ROM and elevated inflammatory markers. MRI demonstrated a large glenohumeral effusion with synovitis, and arthrocentesis confirmed septic arthritis (SA). She required subtotal bursectomy. Intraoperative joint cultures grew Streptococcus gordonii. She completed 6 weeks of antibiotics and is undergoing physical therapy for post-infectious adhesive capsulitis. SA is most commonly due to Staphylococcus aureus and β-haemolytic streptococci, and rarely due to viridans group streptococci including S. gordonii. To avoid inadvertent injection into the glenohumeral joint, vaccination should be performed posteriorly and inferiorly into the deltoid musculature. Progressive pain, fever or decreased passive ROM following vaccination should raise concern for SA. Given its rarity, however, concern for secondary SA should not affect the general population’s consideration for vaccination.