Computational bioprospecting of phytoconstituents as potential inhibitors for peptide deformylase from Streptococcus oralis: An opportunistic pathogen.

Streptococcus oralis an opportunistic bacterium has been reported to be involved in various blood borne infections like subacute bacterial endocarditis, septicemia, bacterial meningitis and in some cases dental caries too. Among various targets the peptide deformylase, of S.oralis appears to be most potent druggable target as it is involved in protein synthesis is opted for the current study. Due to unavailability of PDB structure of peptide deformylase from S. oralis the study initiates with homology modelling of the protein and 6OW2 of S pneumoniae is considered as the template. Thereafter, Molecular docking, Molecular dynamic simulation, ADME analysis, and MMPBSA analysis was carried out to explore the inhibitory potential of phyto-constituents as potential inhibitors for Peptide deformylase from S.oralis. Actinonin was considered as reference drug. Among 2370 phyto compounds the best observations were recorded for A1-Barrigenol (IMPHY010984) with binding affinity of -8.5 kcal/mol. Calculated RMSD, RMSF, Binding Free Energy for IMPHY010984 averaged at about 0.10 ± 0.03 nm, 0.08 ± 0.05 nm, 131 ± 21 kJ/mol respectively whereas the RMSD, RMSF, Binding Free Energy recorded for reference drug averaged at about 0.19 ± 0.04 nm, 0.11 ± 0.08 nm, -94 ± 18 kJ/mol respectively. Based on in silico observations IMPHY010984 is proved out as superior candidate over reference drug. The study reflects the potential of IMPHY010984 as prophylactic therapeutics for S.oralis.

Combinations of Daptomycin plus Ceftriaxone, but Not Ascending Daptomycin Dose-Regimens, Are Effective in Experimental Endocarditis Caused by Streptococcus mitis-oralis Strains: Target Tissue Clearances and Prevention of Emergence of Daptomycin-Resistance.

The Streptococcus mitis-oralis subgroup of the viridans group streptococci (VGS) are the most common cause of infective endocarditis (IE) in many parts of the world. These organisms are frequently resistant in vitro to standard ß-lactams (e.g., penicillin; ceftriaxone [CRO]), and have the notable capacity for rapidly developing high-level and durable daptomycin resistance (DAP-R) during exposures in vitro, ex vivo, and in vivo. In this study, we used 2 prototypic DAP-susceptible (DAP-S) S. mitis-oralis strains (351; and SF100), which both evolved stable, high-level DAP-R in vitro within 1 to 3 days of DAP passage (5 to 20 µg/mL DAP). Of note, the combination of DAP + CRO prevented this rapid emergence of DAP-R in both strains during in vitro passage. The experimental rabbit IE model was then employed to quantify both the clearance of these strains from multiple target tissues, as well as the emergence of DAP-R in vivo under the following treatment conditions: (i) ascending DAP-alone dose-strategies encompassing human standard-dose and high-dose-regimens; and (ii) combinations of DAP + CRO on these same metrics. Ascending DAP-alone dose-regimens (4 to 18 mg/kg/d) were relatively ineffective at either reducing target organ bioburdens or preventing emergence of DAP-R in vivo. In contrast, the combination of DAP (4 or 8 mg/kg/d) + CRO was effective at clearing both strains from multiple target tissues (often with sterilization of bio-burdens in such organs), as well as preventing the emergence of DAP-R. In patients with serious S. mitis-oralis infections such as IE, especially caused by strains exhibiting intrinsic ß-lactam resistance, initial therapy with combinations of DAP + CRO may be warranted.

Spatiotemporal monitoring of a periodontal multispecies biofilm model: demonstration of prebiotic treatment responses.

Biofilms are complex polymicrobial communities which are often associated with human infections such as the oral disease periodontitis. Studying these complex communities under controlled conditions requires in vitro biofilm model systems that mimic the natural environment as close as possible. This study established a multispecies periodontal model in the drip flow biofilm reactor in order to mimic the continuous flow of nutrients at the air-liquid interface in the oral cavity. The design is engineered to enable real-time characterization. A community of five bacteria, Streptococcus gordonii-GFPmut3*, Streptococcus oralis-GFPmut3*, Streptococcus sanguinis-pVMCherry, Fusobacterium nucleatum, and Porphyromonas gingivalis-SNAP26 is visualized using two distinct fluorescent proteins and the SNAP-tag. The biofilm in the reactor develops into a heterogeneous, spatially uniform, dense, and metabolically active biofilm with relative cell abundances similar to those in a healthy individual. Metabolic activity, structural features, and bacterial composition of the biofilm remain stable from 3 to 6 days. As a proof of concept for our periodontal model, the 3 days developed biofilm is exposed to a prebiotic treatment with L-arginine. Multifaceted effects of L-arginine on the oral biofilm were validated by this model setup. L-arginine showed to inhibit growth and incorporation of the pathogenic species and to reduce biofilm thickness and volume. Additionally, L-arginine is metabolized by Streptococcus gordonii-GFPmut3* and Streptococcus sanguinis-pVMCherry, producing high levels of ornithine and ammonium in the biofilm. In conclusion, our drip flow reactor setup is promising in studying spatiotemporal behavior of a multispecies periodontal community.ImportancePeriodontitis is a multifactorial chronic inflammatory disease in the oral cavity associated with the accumulation of microorganisms in a biofilm. Not the presence of the biofilm as such, but changes in the microbiota (i.e., dysbiosis) drive the development of periodontitis, resulting in the destruction of tooth-supporting tissues. In this respect, novel treatment approaches focus on maintaining the health-associated homeostasis of the resident oral microbiota. To get insight in dynamic biofilm responses, our research presents the establishment of a periodontal biofilm model including Streptococcus gordonii, Streptococcus oralis, Streptococcus sanguinis, Fusobacterium nucleatum, and Porphyromonas gingivalis. The added value of the model setup is the combination of simulating continuously changing natural mouth conditions with spatiotemporal biofilm profiling using non-destructive characterization tools. These applications are limited for periodontal biofilm research and would contribute in understanding treatment mechanisms, short- or long-term exposure effects, the adaptation potential of the biofilm and thus treatment strategies.

Invasive Streptococcus oralis Expressing Serotype 3 Pneumococcal Capsule, Japan.

We report 2 adult cases of invasive disease in Japan caused by Streptococcus oralis that expressed the serotype 3 pneumococcal capsule and formed mucoid colonies. Whole-genome sequencing revealed that the identical serotype 3 pneumococcal capsule locus and hyl fragment were recombined into the genomes of 2 distinct S. oralis strains.

Clinical and microbiological features of intratumor abscess with bloodstream infection caused by Plesiomonas shigelloides, Citrobacter freundii, Streptococcus mitis/oralis, Clostridium perfringens, and Candida albicans in a patient with cholangiocarcinoma: A case report.

Plesiomonas shigelloides is a gram-negative facultative anaerobic bacillus, usually found in soil and freshwater, which causes self-limited diarrhea, although reports of bacteremia are rare. Here, we report the first case of an intratumoral abscess with mixed bacteremia caused by P. shigelloides, Citrobacter freundii, Streptococcus mitis/oralis, Clostridium perfringens, and Candida albicans in a patient with recurrent postoperative cholangiocarcinoma. A 77-year-old man with hilar cholangiocarcinoma and hypertension was admitted to our hospital with fever and abdominal pain. He had visited Vietnam for 3 years, 20 years ago. Abdominal computed tomography showed air within the recurrent tumor at the left liver lobectomy resection margin site, which was diagnosed as an intratumor abscess perforating the intestinal tract. P. shigelloides, C. freundii, S. mitis/oralis, C. perfringens, and C. albicans were isolated in blood culture. P. shigelloides was identified using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS) and 16S ribosomal RNA (16S rRNA) sequencing. Piperacillin-tazobactam was administered for almost a week, ampicillin-sulbactam and levofloxacin for almost 3 weeks, and antifungal agents for almost 2 weeks, and the patient was discharged thereafter. Although bloodstream infections caused by P. shigelloides in patients with cancer are extremely rare, long-term colonization and the potential for future intra-abdominal infections were implicated.

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 min, RNA was extracted for dual transcriptome sequencing (RNA-Seq) 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 those to coaggregation with other oral bacteria. Targeting the key genes that are upregulated during interspecies interactions may be a powerful approach to control the development of biofilm and maintain oral health.

Streptococcus oralis MitraClip endocarditis following a dental procedure: a case report.

BACKGROUND: Transcatheter edge-to-edge mitral valve repair using the MitraClip device is increasingly used for high surgical risk patients with severe mitral regurgitation (MR). Previous guidelines for infective endocarditis prophylaxis prior to dental procedures focused on high-risk patients, but without explicit recommendation for MitraClip recipients. We believe this could be the first reported case to identify Streptococcus oralis as the causative organism. CASE PRESENTATION: An 87-year-old male with severe MR treated with two MitraClip devices three months prior to index admission, presented with worsening malaise and intermittent chills on a background of multiple comorbid conditions. The patient had dental work a month prior to presentation, including a root canal procedure, without antibiotic prophylaxis. Vitals were significant for fever and hypotension. On physical examination, there was a holosystolic murmur at the apex radiating to the axilla, bilateral pitting edema in the lower extremities, and elevated jugular venous pulsation. A transthoracic echocardiogram showed severe MR with a possible echodensity on the mitral valve, prompting a transesophageal echocardiogram, which demonstrated a pedunculated, mobile mass on the posterior leaflet of the mitral valve. Five blood cultures grew gram positive cocci in pairs and chains, later identified as Streptococcus oralis, with minimum inhibitory concentration to penicillin 0.06 mg/L. Initial empiric antibiotics were switched to ceftriaxone 2 gr daily and subsequent blood cultures remained negative. However, the patient developed pulmonary edema and worsening hemodynamic instability requiring vasopressors. As surgical risk for re-operation was considered prohibitive, the decision was made to continue medical management and comfort-directed care. The patient died a week later. CONCLUSIONS: Despite low incidence, infective endocarditis should be included in the differential among MitraClip recipients. The explicit inclusion of this growing patient population in the group requiring prophylaxis prior to dental procedures in the 2020 ACC/AHA valvular heart disease guidelines is an important step forward.

Dual-Light Photodynamic Therapy Effectively Eliminates Streptococcus Oralis Biofilms.

PURPOSE: During cancer treatment, oral mucositis due to radiotherapy or chemotherapy often leads to disruption of the oral mucosa, enabling microbes to invade bloodstream. Viridans streptococcal species are part of the healthy oral microbiota but can be frequently isolated from the blood of neutropenic patients.  We have previously shown the antibacterial efficacy of dual-light, the combination of antibacterial blue light (aBL) and indocyanine green photodynamic therapy (aPDT). METHODS: Here, we investigated the dual-light antibacterial action against four-day Streptococcus oralis biofilm. In addition, while keeping the total radiant exposure constant at 100J/cm2, we investigated the effect of changing the different relative light energies of aBL and aPDT to the antibacterial potential. RESULTS: The dual-light had a significant antibacterial effect in all the tested combinations. CONCLUSION: Dual-light can be used as an effective disinfectant against S. oralis biofilm.

Pathogenic and antimicrobial resistance genes in Streptococcus oralis strains revealed by comparative genome analysis.

Streptococcus oralis is an early colonizer bacterium in dental plaques and is considered a potential pathogen of infective endocarditis (IE) disease. In this study, we built a complete genome map of Streptococcus oralis strain SOT, Streptococcus oralis strain SOD and Streptococcus infantis strain SO and performed comparative genomic analysis among these three strains. The results showed that there are five genomic islands (GIs) in strain SOT and one CRISPR in strain SOD. Each genome harbors various pathogenic genes related to diseases and drug resistance, while the antibiotic resistance genes in strains SOT and SOD were quite similar but different from those in strain SO. In addition, we identified 17 main virulence factors and capsule-related genes in three strains. These results suggest the pathogenic potential of Streptococcus strains, which lay a foundation for the prevention and treatment of a Streptococcus oralis infection.

Evaluation of the Antimicrobial Effect of Thymoquinone against Different Dental Pathogens: An In Vitro Study.

This study aimed to evaluate the antimicrobial effect of Thymoquinone (TQ) on four different oral microorganisms. Minimum Bactericidal Concentration (MBC), Minimum Inhibition Concentration (MIC), Broth microdilution, and Well diffusion tests were used to determine the optimum antimicrobial concentrations of TQ against Streptococcus salivarius, Streptococcus oralis, Streptococcus mutans, and Staphylococcus aureus over 1, 3, 6, 12 and 24 h. Chlorhexidine 0.12% was selected as a positive control. The inhibitory effect of TQ on bacterial growth was most noticeable with S. salivarius, while the least affected was S. aureus. TQ's MBC and MIC for S. oralis and S. aureus were comparable 2 mg/mL and 3 mg/mL, respectively. S. salivarius was most resistant to TQ and displayed a value of 5 mg/mL and 4 mg/mL for MIC and MBC, respectively. The viable count of different strains after exposure to TQ's MBC values was most noticeable with S. aureus followed by S. oralis and S. mutans, while S. salivarius was least affected. This study emphasized the promising antimicrobial effect of TQ against the four main oral microorganisms. It has a potential preventive effect against dental caries as well as other oral diseases.

Commensal and pathogenic biofilms differently modulate peri-implant oral mucosa in an organotypic model.

The impact of oral commensal and pathogenic bacteria on peri-implant mucosa is not well understood, despite the high prevalence of peri-implant infections. Hence, we investigated responses of the peri-implant mucosa to Streptococcus oralis or Aggregatibacter actinomycetemcomitans biofilms using a novel in vitro peri-implant mucosa-biofilm model. Our 3D model combined three components, organotypic oral mucosa, implant material, and oral biofilm, with structural assembly close to native situation. S. oralis induced a protective stress response in the peri-implant mucosa through upregulation of heat shock protein (HSP70) genes. Attenuated inflammatory response was indicated by reduced cytokine levels of interleukin-6 (IL-6), interleukin-8 (CXCL8), and monocyte chemoattractant protein-1 (CCL2). The inflammatory balance was preserved through increased levels of tumor necrosis factor-alpha (TNF-α). A. actinomycetemcomitans induced downregulation of genes important for cell survival and host inflammatory response. The reduced cytokine levels of chemokine ligand 1 (CXCL1), CXCL8, and CCL2 also indicated a diminished inflammatory response. The induced immune balance by S. oralis may support oral health, whereas the reduced inflammatory response to A. actinomycetemcomitans may provide colonisation advantage and facilitate later tissue invasion. The comprehensive characterisation of peri-implant mucosa-biofilm interactions using our 3D model can provide new knowledge to improve strategies for prevention and therapy of peri-implant disease.

Bloodstream infection by multidrug-resistant Streptococcus oralis in a leukemic patient with febrile neutropenia after hematopoietic stem cell transplantation.

We reported the case of a patient with leukemia who developed febrile neutropenia after hematopoietic stem cell transplantation. Blood culture results revealed the presence of Streptococcus oralis, while antimicrobial susceptibility testing showed the resistance to penicillin and cephem. Furthermore, isolates were not susceptible to either meropenem or daptomycin but not to vancomycin. S oralis is known to belong to Streptococcus mitis group and be a causative agent of bacteremia in the neutropenic patients, but multidrug resistance of S oralis is rare. Our findings suggest that we might pay attention to the emergence of the microorganisms acquiring multidrug resistance in neutropenic patients.

Effects of a sub-minimum inhibitory concentration of chlorhexidine gluconate on the development of in vitro multi-species biofilms.

Following antimicrobial administrations in oral environments, bacteria become exposed to a sub-minimum inhibitory concentration (sub-MIC), which can induce in vitro single-species biofilms. This study explored the effects of chlorhexidine gluconate (CHG) at a sub-MIC on in vitro multi-species biofilms comprising Streptococcus mutans, Streptococcus oralis and Actinomyces naeslundii. CHG at a sub-MIC was found to induce in vitro biofilm growth, although the bacterial growth was not significantly different from that in the control. The gene transcription related to S. mutans multi-species biofilm formation with CHG at a sub-MIC was significantly higher than that of the control, but this was not found in S. mutans single-species biofilms. The bio-volume of extracellular polysaccharides with CHG at a sub-MIC was significantly higher than that of the control. This suggests that CHG at a sub-MIC may promote the development of multi-species biofilms by affecting the gene transcription related to S. mutans biofilm formation.

Anti-biofilm activity of a novel pit and fissure self-adhesive sealant modified with metallic monomers.

Dental plaque is a biofilm composed of a complex oral microbial community. The accumulation of plaque in the pit and fissures of dental elements often leads to the development of tooth decay (dental caries). Here, potent anti-biofilm materials were developed by incorporating zinc methacrylates or di-n-butyl-dimethacrylate-tin into the light-curable sealant and their physical, mechanical, and biological properties were evaluated. The data revealed that 5% di-n-butyl-dimethacrylate-tin (SnM 5%) incorporated sealant showed strong anti-biofilm efficacy against various single-species (Streptococcus mutans or Streptococcus oralis or Candida albicans) and S. mutans-C. albicans cross-kingdom dual-species biofilms without either impairing the mechanical properties of the sealant or causing cytotoxicities against mouse fibroblasts. The findings indicate that the incorporation of SnM 5% in the experimental pit and fissure self-adhesive sealant may have the potential to be part of current chemotherapeutic strategies to prevent the formation of cariogenic oral biofilms that cause dental caries.

Material characterization and Streptococcus oralis adhesion on Polyetheretherketone (PEEK) and titanium surfaces used in implantology.

The aim of this study was to evaluate the interaction between Streptococcus oralis and Polyetheretherketone (PEEK), a novel material recently introduced in implantology. The topographical characterization and the Streptococcus oralis adhesion on this material were compared with other titanium surfaces, currently used for the production of dental implants: machined and double etched (DAE). The superficial micro-roughness of the PEEK discs was analyzed by scanning electron microscopy (SEM) and, the Energy Dispersive Spectrometer (EDS) analyzed their chemical composition. Atomic Force Microscopy (AFM) was used to characterize the micro-topography and the sessile method to evaluate the wettability of the samples. Microbiological analysis measured the colony forming units (CFUs), the biomass (OD570 detection) and the cell viability after 24 and 48 h after Streptococcus oralis cultivation on the different discs, that were previously incubated with saliva. Results showed that PEEK was characterized by a micro-roughness that was similar to machined titanium but at nano-level the nano-roughness was significantly higher in respect to the other samples. The EDS showed that PEEK superficial composition was characterized mainly by Carbonium and Oxygen. The hydrophilicity and wetting properties of PEEK were similar to machined titanium; on the contrary, double etched discs (DAE) samples were characterized by significantly higher levels (p < 0.05). PEEK was characterized by significant lower CFUs, biomass and viable cells in respect to the titanium surfaces. No differences were found between machined and DAE. The anti-adhesive and antibacterial properties showed by PEEK at 24 and 48 h against a pioneer such as S. oralis, could have an important role in the prevention of all pathologies connected with biofilm formation, like peri-implantitis in dentistry or prosthetic failures in orthopedics.

The Bacterial Anti-Adhesive Activity of Double-Etched Titanium (DAE) as a Dental Implant Surface.

This work aimed to compare the capability of Streptococcus oralis to adhere to a novel surface, double-etched titanium (DAE), in respect to machined and single-etched titanium. The secondary outcome was to establish which topographical features could affect the interaction between the implant surface and bacteria. The samples' superficial features were characterized using scanning electron microscopy (SEM) and energy dispersive x-ray spectrometry (EDS), and the wetting properties were tested through sessile methods. The novel surface, the double-etched titanium (DAE), was also analyzed with atomic force microscopy (AFM). S. oralis was inoculated on discs previously incubated in saliva, and then the colony-forming units (CFUs), biomass, and cellular viability were measured at 24 and 48h. SEM observation showed that DAE was characterized by higher porosity and Oxygen (%) in the superficial layer and the measurement of the wetting properties showed higher hydrophilicity. AFM confirmed the presence of a higher superficial nano-roughness. Microbiological analysis showed that DAE discs, coated by pellicle's proteins, were characterized by significantly lower CFUs at 24 and 48 h with respect to the other two groups. In particular, a significant inverse relationship was shown between the CFUs at 48 h and the values of the wetted area and a direct correlation with the water contact angle. The biomass at 24 h was slightly lower on DAE, but results were not significant concerning the other groups, both at 24 and 48 h. The DAE treatment not only modifies the superficial topography and increased hydrophilicity, but it also increases the Oxygen percentage in the superficial layer, which could contribute to the inhibition of S. oralis adhesion. DAE can be considered a promising treatment for titanium implants to counteract a colonization pioneer microorganism, such as S. oralis.

[Creation of a molecular genetic test system for early diagnosis and evaluation of the effectiveness of treatment of inflammatory periodontal diseases.]

Inflammatory periodontal diseases represent a serious dental and general medical problem due to the high prevalence among the adult population, the presence of clinical forms leading to the destruction of the dentition and tooth loss, insufficient treatment effectiveness and the frequency of relapse, including in connection with the formation of biofilms. A molecular genetic test system has been developed to evaluate the content of periodontopathogenic microorganisms Porphyromonas gingivalis, Treponema denticola, Streptococcus oralis, Streptococcus sanguis and Streptococcus sobrinus in the contents of periodontal pockets. The analytical characteristics of the test system were determined, and testing was carried out on clinical samples of patients with chronic generalized periodontitis of moderate severity. The constructed diagnostic kit allowed us to conduct a comparative analysis of the effectiveness of various types of treatment of inflammatory periodontal diseases based on quantitative data on the content of bacteria in the contents of periodontal pockets.

Phosphatidylcholine Biosynthesis in Mitis Group Streptococci via Host Metabolite Scavenging.

The mitis group streptococci include the major human pathogen Streptococcus pneumoniae and the opportunistic pathogens Streptococcus mitis and Streptococcus oralis, which are human oral cavity colonizers and agents of bacteremia and infective endocarditis in immunocompromised patients. Bacterial membrane lipids play crucial roles in microbe-host interactions; for many pathogens, however, the composition of the membrane is poorly understood. In this study, we characterized the lipidomes of selected species of mitis group streptococci and investigated the mechanistic basis for biosynthesis of the phospholipid phosphatidylcholine (PC). PC is a major lipid in eukaryotic cellular membranes, but it is considered to be comparatively rare in bacterial taxa. Using liquid chromatography-mass spectrometry in conjunction with stable isotope tracing, we determined that mitis group streptococci synthesize PC via a rare host-metabolite-scavenging pathway, the glycerophosphocholine (GPC) pathway, which is largely uncharacterized in bacteria. Our work demonstrates that mitis group streptococci, including S. pneumoniae, remodel their membranes in response to the major human metabolites GPC and lysophosphatidylcholine.IMPORTANCE We lack fundamental information about the composition of the cellular membrane even for the best-studied pathogens of critical significance for human health. The mitis group streptococci are closely linked to humans in health and disease, but their membrane biology is poorly understood. Here, we demonstrate that these streptococci scavenge major human metabolites and use them to synthesize the membrane phospholipid PC. Our work is significant because it identifies a mechanism by which the major human pathogen S. pneumoniae and the primary human oral colonizers S. mitis and S. oralis remodel their membranes in response to host metabolites.

Streptococcus oralis subsp. dentisani Produces Monolateral Serine-Rich Repeat Protein Fibrils, One of Which Contributes to Saliva Binding via Sialic Acid.

Our studies reveal that the oral colonizer and cause of infective endocarditis Streptococcus oralis subsp. dentisani displays a striking monolateral distribution of surface fibrils. Furthermore, our data suggest that these fibrils impact the structure of adherent bacterial chains. Mutagenesis studies indicate that these fibrils are dependent on three serine-rich repeat proteins (SRRPs), here named fibril-associated protein A (FapA), FapB, and FapC, and that each SRRP forms a different fibril with a distinct distribution. SRRPs are a family of bacterial adhesins that have diverse roles in adhesion and that can bind to different receptors through modular nonrepeat region domains. Amino acid sequence and predicted structural similarity searches using the nonrepeat regions suggested that FapA may contribute to interspecies interactions, that FapA and FapB may contribute to intraspecies interactions, and that FapC may contribute to sialic acid binding. We demonstrate that a fapC mutant was significantly reduced in binding to saliva. We confirmed a role for FapC in sialic acid binding by demonstrating that the parental strain was significantly reduced in adhesion upon addition of a recombinantly expressed, sialic acid-specific, carbohydrate binding module, while the fapC mutant was not reduced. However, mutation of a residue previously shown to be essential for sialic acid binding did not decrease bacterial adhesion, leaving the precise mechanism of FapC-mediated adhesion to sialic acid to be defined. We also demonstrate that the presence of any one of the SRRPs is sufficient for efficient biofilm formation. Similar structures were observed on all infective endocarditis isolates examined, suggesting that this distribution is a conserved feature of this S. oralis subspecies.

Mutations in cdsA and pgsA Correlate with Daptomycin Resistance in Streptococcus mitis and S. oralis.

We investigated the ability of several recent clinical viridans group streptococci (VGS) bloodstream isolates (Streptococcus mitis/S. oralis subgroup) from daptomycin (DAP)-naive patients to develop DAP resistance in vitro All strains rapidly developed high-level and stable DAP resistance. Substitutions in two enzymes involved in the cardiolipin biosynthesis pathway were identified, i.e., CdsA (phosphatidate cytidylyltransferase) and PgsA (CDP-diacylglycerol-glycerol-3-phosphate-3-phosphatidyltransferase). These mutations were associated with complete disappearance of phosphatidylglycerol and cardiolipin from cell membranes. DAP interactions with the cell membrane differed in isolates with PgsA versus CdsA substitutions.