Clinical isolates of Streptococcus mitis/oralis-related species with reduced carbapenem susceptibility, harboring amino acid substitutions in penicillin-binding proteins in Japan.

Streptococcus mitis/oralis group isolates with reduced carbapenem susceptibility have been reported, but its isolation rate in Japan is unknown. We collected 356 clinical α-hemolytic streptococcal isolates and identified 142 of them as S. mitis/oralis using partial sodA sequencing. The rate of meropenem non-susceptibility was 17.6% (25/142). All 25 carbapenem-non-susceptible isolates harbored amino acid substitutions in/near the conserved motifs in PBP1A, PBP2B, and PBP2X. Carbapenem non-susceptibility is common among S. mitis/oralis group isolates in Japan.

Developing multispecies quorum-sensing modulators based on the Streptococcus mitis competence-stimulating peptide.

Bacteria utilize quorum sensing (QS) to coordinate many group behaviors. As such, QS has attracted significant attention as a potential mean to attenuate bacterial infectivity without introducing selective pressure for resistance development. Streptococcus mitis, a human commensal, acts as a genetic diversity reservoir for Streptococcus pneumoniae, a prevalent human pathogen. S. mitis possesses a typical comABCDE competence regulon QS circuitry; however, the competence-stimulating peptide (CSP) responsible for QS activation and the regulatory role of the competence regulon QS circuitry in S. mitis are yet to be explored. We set out to delineate the competence regulon QS circuitry in S. mitis, including confirming the identity of the native CSP signal, evaluating the molecular mechanism that governs CSP interactions with histidine kinase receptor ComD leading to ComD activation, and defining the regulatory roles of the competence regulon QS circuitry in initiating various S. mitis phenotypes. Our analysis revealed important structure-activity relationship insights of the CSP signal and facilitated the development of novel CSP-based QS modulators. Our analysis also revealed the involvement of the competence regulon in modulating competence development and biofilm formation. Furthermore, our analysis revealed that the native S. mitis CSP signal can modulate QS response in S. pneumoniae. Capitalizing on this crosstalk, we developed a multispecies QS modulator that activates both the pneumococcus ComD receptors and the S. mitis ComD-2 receptor with high potencies. The novel scaffolds identified herein can be utilized to evaluate the effects temporal QS modulation has on S. mitis as it inhabits its natural niche.

Genomic Features and Comparative Genomic Analysis of Streptococcus sp. v1. nov., Isolated from an Endophthalmitis Patient.

Endophthalmitis is an acute inflammatory intraocular condition that can cause permanent vision loss. The treatment strategy and visual outcome partly depend on the identification of the agents of pathogens. In this study, metagenomic sequencing was conducted to investigate the microbial and antibiotic resistance genes (ARGs) composition in the vitreous (intraocular body fluid) of an endophthalmitis patient, who progressed rapidly and accompanied by severe pain. Metagenomic sequencing data revealed that the vitreous sample was predominated by Streptococcus, with a low-diversity microbiome in the vitreous. This strain harbor's the ARGs mainly against beta-lactam, macrolide-lincosamide-streptogramin, and multidrug. Additionally, metagenome-assembled genome sequence of Streptococcus sp. v1. nov. was identified. The Tetra Correlation Search (TCS) analysis uncovered that the closest relative of the Streptococcus sp. v1. nov. was Streptococcus mitis SK321. Pan/core genome analysis for Streptococcus sp. v1. nov. and TCS top 25 hits strains revealed that most unique genes of Streptococcus sp. v1. nov. were linked to ATP-binding cassette transport system, which could indicate unique virulence and pathogenic potentials of Streptococcus sp. v1. nov. In addition, a total of 7 virulence factors were identified, and the overwhelming of them were classified into "offensive virulence factors". The high pathogenicity of Streptococcus sp. v1. nov. could be a reason for the patient's rapid disease progression. Our study was first isolated an ocular pathogen with highly virulent based on metagenomic sequencing and bioinformatics analysis, which has important reference value for revealing the composition and genome characteristics of pathogens in endophthalmitis patient in the future.

Bacterial multispecies interaction mechanisms dictate biogeographic arrangement between the oral commensals Corynebacterium matruchotii and Streptococcus mitis.

IMPORTANCE: As the microbiome era matures, the need for mechanistic interaction data between species is crucial to understand how stable microbiomes are preserved, especially in healthy conditions where the microbiota could help resist opportunistic or exogenous pathogens. Here we reveal multiple mechanisms of interaction between two commensals that dictate their biogeographic relationship to each other in previously described structures in human supragingival plaque. Using a novel variation for chemical detection, we observed metabolite exchange between individual bacterial cells in real time validating the ability of these organisms to carry out metabolic crossfeeding at distal and temporal scales observed in vivo. These findings reveal one way by which these interactions are both favorable to the interacting commensals and potentially the host.

Streptococcus Mitis Endocarditis Associated with Early Gastric Carcinoma.

We report a case of Streptococcus mitis endocarditis associated with early gastric carcinoma. A 71-year-old man who had been diagnosed with aortic regurgitation (AR) two years previously was referred for valve surgery and evaluation of elevated inflammatory markers. Four months previously, atrophic gastritis, early gastric adenocarcinoma, and colon polyp had been identified in the patient during endoscopy. However, Helicobacter pylori testing was negative. On admission, he had no dental diseases or recent oral procedures. Echocardiography demonstrated severe AR and mobile vegetation on the aortic valve. Magnetic resonance imaging revealed cerebral embolism and spondylodiscitis. Blood cultures grew Streptococcus mitis. At surgery, destruction of the left cusp with vegetation and a perforation of the non-coronary cusp were found; in addition, aortic valve replacement was performed. Although the association between Streptococcus bovis bacteremia and colon neoplasm is well recognized, the association between Streptococcus mitis endocarditis and gastrointestinal carcinoma should also be kept in mind.

Human Serum Supplementation Promotes Streptococcus mitis Growth and Induces Specific Transcriptomic Responses.

Streptococcus mitis is a normal member of the human oral microbiota and a leading opportunistic pathogen causing infective endocarditis (IE). Despite the complex interactions between S. mitis and the human host, understanding of S. mitis physiology and its mechanisms of adaptation to host-associated environments is inadequate, especially compared with other IE bacterial pathogens. This study reports the growth-promoting effects of human serum on S. mitis and other pathogenic streptococci, including S. oralis, S. pneumoniae, and S. agalactiae. Using transcriptomic analyses, we identified that, with the addition of human serum, S. mitis downregulates uptake systems for metal ions and sugars, fatty acid biosynthetic genes, and genes involved in stress response and other processes related with growth and replication. S. mitis upregulates uptake systems for amino acids and short peptides in response to human serum. Zinc availability and environmental signals sensed by the induced short peptide binding proteins were not sufficient to confer the growth-promoting effects. More investigation is required to establish the mechanism for growth promotion. Overall, our study contributes to the fundamental understanding of S. mitis physiology under host-associated conditions. IMPORTANCE S. mitis is exposed to human serum components during commensalism in the human mouth and bloodstream pathogenesis. However, the physiological effects of serum components on this bacterium remain unclear. Using transcriptomic analyses, S. mitis biological processes that respond to the presence of human serum were revealed, improving the fundamental understanding of S. mitis physiology in human host conditions.

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.

An Isolate of Streptococcus mitis Displayed In Vitro Antimicrobial Activity and Deleterious Effect in a Preclinical Model of Lung Infection.

Microbiota studies have dramatically increased over these last two decades, and the repertoire of microorganisms with potential health benefits has been considerably enlarged. The development of next generation probiotics from new bacterial candidates is a long-term strategy that may be more efficient and rapid with discriminative in vitro tests. Streptococcus strains have received attention regarding their antimicrobial potential against pathogens of the upper and, more recently, the lower respiratory tracts. Pathogenic bacterial strains, such as non-typable Haemophilus influenzae (NTHi), Pseudomonas aeruginosa (P. aeruginosa) and Staphylococcus aureus (S. aureus), are commonly associated with acute and chronic respiratory diseases, and it could be interesting to fight against pathogens with probiotics. In this study, we show that a Streptococcus mitis (S. mitis) EM-371 strain, isolated from the buccal cavity of a human newborn and previously selected for promising anti-inflammatory effects, displayed in vitro antimicrobial activity against NTHi, P. aeruginosa or S. aureus. However, the anti-pathogenic in vitro activity was not sufficient to predict an efficient protective effect in a preclinical model. Two weeks of treatment with S. mitis EM-371 did not protect against, and even exacerbated, NTHi lung infection.

Novel Multilocus Sequence Typing and Global Sequence Clustering Schemes for Characterizing the Population Diversity of Streptococcus mitis.

Streptococcus mitis is a common oral commensal and an opportunistic pathogen that causes bacteremia and infective endocarditis; however, the species has received little attention compared to other pathogenic streptococcal species. Effective and easy-to-use molecular typing tools are essential for understanding bacterial population diversity and biology, but schemes specific for S. mitis are not currently available. We therefore developed a multilocus sequence typing (MLST) scheme and defined sequence clusters or lineages of S. mitis using a comprehensive global data set of 322 genomes (148 publicly available and 174 newly sequenced). We used internal 450-bp sequence fragments of seven housekeeping genes (accA, gki, hom, oppC, patB, rlmN, and tsf) to define the MLST scheme and derived the global S. mitis sequence clusters using the PopPUNK clustering algorithm. We identified an initial set of 259 sequence types (STs) and 258 global sequence clusters. The schemes showed high concordance (100%), capturing extensive S. mitis diversity with strains assigned to multiple unique STs and global sequence clusters. The tools also identified extensive within- and between-host S. mitis genetic diversity among isolates sampled from a cohort of healthy individuals, together with potential transmission events, supported by both phylogeny and pairwise single nucleotide polymorphism (SNP) distances. Our novel molecular typing and strain clustering schemes for S. mitis allow for the integration of new strain data, are electronically portable at the PubMLST database (https://pubmlst.org/smitis), and offer a standardized approach to understanding the population structure of S. mitis. These robust tools will enable new insights into the epidemiology of S. mitis colonization, disease and transmission.

Demystifying interactions between micro organisms in oral candidiasis biofilm: the key to enhancing treatments

Introduction: candida albicans is a fungal pathogen that can provoke diseases ranging from oral infections to life-threatening systemic disorders. It is now recognized that oral bacteria, such as the genus Streptococcus, establish synergistic relationships with C. albicans, which could potentially increase the fungi's virulence and pathogenicity. Objective: this narrative review aimed to discuss the Candida-Streptococcus mechanisms of interactions and their contribution to increasing oral candidiasis severity. In addition, it provides a background of biofilm formation and potential therapeutical targets. Sources of Data: searches for papers in English were performed in the Pubmed database until May 2022. MeSH and free terms related to the field were used. In vitro studies were selected, tabulated, and qualitative and quantitative data were analyzed descriptively. Synthesis of Data: among the early colonizers bacteria, evidence pointed out that S. gordonnii and S. oralis have major implications in oral candidiasis, in which mixed biofilms increase the infection severity and challenge the host's defense. On the other hand, the outcomes of the interaction between C. albicans and S. mitis, S. sanguinis, or S. mutans remain little explored in the oral candidiasis scenario, albeit evidence pointed out an enhanced fungus population and virulence factors. Conclusion: overall, considering the polymicrobial profile of the infection and the potential to increase Candida-related disease severity, therapeutical strategies should also consider bacteria management.

Introdução: candida albicans é um patógeno fúngico que pode provocar doenças que variam de infecções orais a distúrbios sistêmicos com risco de vida. Hoje se reconhece que as bactérias orais, como o gênero Streptococcus, estabelecem relações sinérgicas com C. albicans, o que pode potencialmente aumentar a virulência e patogenicidade do fungo. Objetivo: esta revisão narrativa teve como objetivo discutir os mecanismos de interação Candida-Streptococcus e sua contribuição para o agravamento da candidíase oral. Além disso, fornece uma breve explanação sobre a formação do biofilme e potenciais alvos terapêuticos. Fonte dos dados: foi realizada pesquisa na base de dados Pubmed para a busca de artigos publicados em Inglês até maio de 2022. Para isso, foram utilizados descritores relacionados ao tema. Estudos in vitro foram selecionados, tabulados e seus resultados quantitativos e qualitativos analisados descritivamente. Síntese dos dados: entre as bactérias denominadas colonizadores iniciais, evidências apontam que S. gordonnii e S. oralis têm implicações importantes na candidíase oral, na qual biofilmes mistos aumentam a gravidade da infecção e desafiam a defesa do hospedeiro. Por outro lado, os desfechos das interações entre C. albicans e S. mitis, S. sanguinis ou S. mutans permanecem pouco explorados no cenário da candidíase oral, apesar de evidências apontarem um aumento dapopulação fúngica e de fatores de virulência. Conclusão: de maneira geral, considerando o perfil polimicrobiano da infecção e o potencial agravamento das doenças provocadas por Candida spp, as estratégias terapêuticas não devem estar focadas apenas no fungo, mas também devem considerar o manejo da bactéria.

Oral mitis group streptococci reduce infectivity of influenza A virus via acidification and H2O2 production.

Members of the mitis group streptococci are the most abundant inhabitants of the oral cavity and dental plaque. Influenza A virus (IAV), the causative agent of influenza, infects the upper respiratory tract, and co-infection with Streptococcus pneumoniae is a major cause of morbidity during influenza epidemics. S. pneumoniae is a member of mitis group streptococci and shares many features with oral mitis group streptococci. In this study, we investigated the effect of viable Streptococcus oralis, a representative member of oral mitis group, on the infectivity of H1N1 IAV. The infectivity of IAV was measured by a plaque assay using Madin-Darby canine kidney cells. When IAV was incubated in growing culture of S. oralis, the IAV titer decreased in a time- and dose-dependent manner and became less than 100-fold, whereas heat-inactivated S. oralis had no effect. Other oral streptococci such as Streptococcus mutans and Streptococcus salivarius also reduced the viral infectivity to a lesser extent compared to S. oralis and Streptococcus gordonii, another member of the oral mitis group. S. oralis produces hydrogen peroxide (H2O2) at a concentration of 1-2 mM, and its mutant deficient in H2O2 production showed a weaker effect on the inactivation of IAV, suggesting that H2O2 contributes to viral inactivation. The contribution of H2O2 was confirmed by an inhibition assay using catalase, an H2O2-decomposing enzyme. These oral streptococci produce short chain fatty acids (SCFA) such as acetic acid as a by-product of sugar metabolism, and we also found that the inactivation of IAV was dependent on the mildly acidic pH (around pH 5.0) of these streptococcal cultures. Although inactivation of IAV in buffers of pH 5.0 was limited, incubation in the same buffer containing 2 mM H2O2 resulted in marked inactivation of IAV, which was similar to the effect of growing S. oralis culture. Taken together, these results reveal that viable S. oralis can inactivate IAV via the production of SCFAs and H2O2. This finding also suggests that the combination of mildly acidic pH and H2O2 at low concentrations could be an effective method to inactivate IAV.

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.

Maternal septicemia caused by Streptococcus mitis: a possible link between intra-amniotic infection and periodontitis. Case report and literature review.

BACKGROUND: Intra-amniotic infection has a strong causal association with spontaneous preterm birth and preterm prelabor rupture of membranes (PPROM). The most common route of intra-amniotic infection is the ascending pathway in which microorganisms from the vagina gain access to the amniotic cavity. Distant microorganisms such as those from the oral cavity have been reported in intra-amniotic infection through hematogenous spreading. CASE PRESENTATION: A 31-year-old gravida 1, para 0 Thai woman at 33+6 weeks' gestation presented with leakage of vaginal fluid and irregular uterine contraction. She developed fever at 4 h after admission and was later diagnosed with acute chorioamnionitis. A Cesarean section was performed to terminate pregnancy. In addition to a blood culture, the cultures of amniotic fluid, vaginal and chorioamniotic membrane swabs were positive for Streptococcus mitis with identical susceptibility profiles. After the delivery and antibiotic prescription, oral examination showed dental caries and chronic periodontitis. CONCLUSIONS: This is the first case report demonstrating maternal septicemia and intra-amniotic infection caused by S. mitis which might be attributed to periodontitis in women presenting with preterm PROM. We highlighted the association of periodontal disease and preterm labor/PROM syndrome. Oral cavity examination should be included in the prenatal care to ensure good dental hygiene.

Streptococcus mitis infective endocarditis in a patient with ventricular septal defect and orthodontic appliances.

We describe a case of a girl in a remote and rural location in Scotland with a perimembranous ventricular septal defect and orthodontic appliances, who developed right-sided infective endocarditis from Streptococcus mitis due to abrasion of the oral mucosa from the arch wire following its adjustment in the dental clinic.Fitting and adjustment of orthodontic appliances are not considered to be high-risk dental procedures and antibiotic prophylaxis is not recommended even for patients at highest risk for infective endocarditis.

DNA isolation methods for Nanopore sequencing of the Streptococcus mitis genome.

Streptococcus mitis is a Gram-positive bacterium, member of the oral commensal microbiota, which can occasionally be the etiologic agent of diseases such as infective endocarditis, bacteraemia and septicaemia. The highly recombinogenic and repetitive nature of the S. mitis genome impairs the assembly of a complete genome relying only on short sequencing reads. Oxford Nanopore sequencing can overcome this limitation by generating long reads, enabling the resolution of genomic repeated regions and the assembly of a complete genome sequence. Since the output of a Nanopore sequencing run is strongly influenced by genomic DNA quality and molecular weight, the DNA isolation is the crucial step for an optimal sequencing run. In the present work, we have set up and compared three DNA isolation methods on two S. mitis strains, evaluating their capability of preserving genomic DNA integrity and purity. Sequencing of DNA isolated with a mechanical lysis-based method, despite being cheaper and quicker, did not generate ultra-long reads (maximum read length of 59516 bases) and did not allow the assembly of a circular complete genome. Two methods based on enzymatic lysis of the bacterial cell wall, followed by either (i) a modified CTAB DNA isolation procedure, or (ii) a DNA purification after osmotic lysis of the protoplasts allowed the sequencing of ultra-long reads up to 107294 and 181199 bases in length, respectively. The reconstruction of a circular complete genome was possible sequencing DNAs isolated using the enzymatic lysis-based methods.

A new perspective on ancient Mitis group streptococcal genetics.

Mitis group Streptococcus are human obligate bacteria residing in the nasopharynx and oral cavity. They comprise both commensal and pathogenic species with the most well-known being Streptococcus pneumoniae - a leading cause of meningitis and pneumonia. A primary difference between the commensal and pathogenic species is the presence of the polysaccharide capsule - a major virulence factor in S. pneumoniae, also present in other commensal species. Our current understanding of the evolutionary divergence of the pathogenic and commensal species has been inferred from extant strains. Ancient genomes can further elucidate streptococcal evolutionary history. We extracted streptococcal genome reads from a 5700-year-old ancient metagenome and worked towards characterizing them. Due to excessive within- and between-species recombination common among streptococci we were unable to parse individual species. Further, the composite reads of the ancient metagenome do not fit within the diversity of any specific extant species. Using a capsular gene database and AT-content analysis we determined that this ancient metagenome is missing polysaccharide synthesis genes integral to streptococcal capsule formation. The presence of multiple zinc metalloproteases suggests that adaptation to host IgA1 had begun and the presence of other virulence factors further implies development of close host-microbe interactions, though the absence of a capsule suggests an inability to cause invasive disease. The presence of specific virulence factors such as pneumolysin implies stable maintenance of such genes through streptococcal evolution that may strengthen their value as anti-pneumococcal vaccine antigens, while maintaining awareness of their potential presence in commensal species. Following from Jensen et al.'s initial analysis we provide historical context for this long time human nasopharyngeal resident, the Mitis group Streptococcus.

Comparison between Antimicrobial and Antibiofilm Activity of Exopolysaccharides (EPS) Extracted from Lactobacillus reuteri and Streptococcus mitis against Oral Bacteria.

Due to the increased resistance to antibiotics and chemical biocides, the use of bacterial exopolysaccharides has been considered. The objective of the current study was to investigate the strength of the antibacterial and antibiofilm activity of EPS extracted from Lactobacillus reuteri and Streptococcus mitis because previous studies showed there were structural differences between EPS, during this study, EPS extracted from Lactobacillus reuteri and Streptococcus miti by ethanol precipitation method and estimated antibacterial and antibiofilm activity against several Oral Bacteria (Staphylococcus aureus, Staphylococcus hominis, Acinetobacter baumannii, Raoultella ornithinolytica, Streptococcus thoraltensis in different concentration as (100,150,200,250,300 mg/ml ), the results showed carbohydrates rate in extracted EPS from L. reuteri and S. mitis were recorded was 85, 80 % respectively.The concentration 100 and 150 mg/ml for EPS from L. reuteri and S. mitis, there was no inhibitory effect, except in S. aureus (1.1±0.10) and S. hominis (1.0±0.10) at 100 mg/ml, 3.1±2.01, 2.1±0.54 mg/ml respectively at 150 mg/ml concentration but no significant differences (P≤0.05). However, the antibacterial effect of that EPSs started at the concentration of 200 and upwards, where different results were recorded between the concentrations of both EPSs against all bacteria isolated (P≤0.05), On the other hand, the effect of EPS from L. reuteri and S. mitis was clear against the formation of biofilm compared with the control, worth mentioning that EPS from L. reuteri was more effective compared with EPS from S. mitis in all isolates (P≤0.05) except for S. thoraltensis where it was noted that the EPS from S. mitis is more effective than EPS from L. reuteri. Through the results obtained in this study, it was noted that the difference in the structural nature of EPS has an important role in its effectiveness as an antibacterial and anti-biofilm formation and, as it was found that the EPS from L. reuteri showed more effectiveness than EPS from S. mitis and thus the mechanism of preventing and inhibiting bacteria depending of the structural nature of EPS.

Streptococcus pneumoniae serotypes that frequently colonise the human nasopharynx are common recipients of penicillin-binding protein gene fragments from Streptococcus mitis.

Streptococcus pneumoniae is an important global pathogen that causes bacterial pneumonia, sepsis and meningitis. Beta-lactam antibiotics are the first-line treatment for pneumococcal disease, however, their effectiveness is hampered by beta-lactam resistance facilitated by horizontal genetic transfer (HGT) with closely related species. Although interspecies HGT is known to occur among the species of the genus Streptococcus, the rates and effects of HGT between Streptococcus pneumoniae and its close relatives involving the penicillin binding protein (pbp) genes remain poorly understood. Here we applied the fastGEAR tool to investigate interspecies HGT in pbp genes using a global collection of whole-genome sequences of Streptococcus mitis, Streptococcus oralis and S. pneumoniae. With these data, we established that pneumococcal serotypes 6A, 13, 14, 16F, 19A, 19F, 23F and 35B were the highest-ranking serotypes with acquired pbp fragments. S. mitis was a more frequent pneumococcal donor of pbp fragments and a source of higher pbp nucleotide diversity when compared with S. oralis. Pneumococci that acquired pbp fragments were associated with a higher minimum inhibitory concentration (MIC) for penicillin compared with pneumococci without acquired fragments. Together these data indicate that S. mitis contributes to reduced ß-lactam susceptibility among commonly carried pneumococcal serotypes that are associated with long carriage duration and high recombination frequencies. As pneumococcal vaccine programmes mature, placing increasing pressure on the pneumococcal population structure, it will be important to monitor the influence of antimicrobial resistance HGT from commensal streptococci such as S. mitis.

Inhibitory effects of propolis and essential oils on oral bacteria.

INTRODUCTION: Propolis is a natural composite balsam. In the past decade, propolis has been extensively investigated as an adjuvant for the treatment of periodontitis. This study aimed to investigate antimicrobial activities of propolis solutions and plant essential oils against some oral cariogenic (Streptococcus mutans, Streptococcus mitis, Streptococcus sanguis, Lactobacillus acidophilus) and periodontopathic bacteria (Actinomyces odontolyticus, Eikenella corrodens, Fusobacterium nucleatum). METHODOLOGY: Determination of the minimum inhibitory concentration (MIC): The antimicrobial activity of propolis and essential oils was investigated by the agar dilution method. Serial dilutions of essential oils were prepared in plates, and the assay plates were estimated to contain 100, 50, 25 and 12.5 µg/mL of active essential oils. Dilutions for propolis were 50, 25, 12.5 and 6.3 µg/mL of active propolis solutions. RESULTS: Propolis solutions dissolved in benzene, diethyl ether and methyl chloride, demonstrated equal effectiveness against all investigated oral bacteria (MIC=12.5 µg/mL). Propolis solution dissolved in acetone displayed MIC of 6.3 µg/mL only for Lactobacillus acidophilus. At the MIC of 12.5 µg/mL, essential oils of Salvia officinalis and Satureja kitaibelii were effective against Streptococcus mutans and Porphyromonas gingivalis, respectively. For the latter, the MIC value of Salvia officinalis was twice higher. CONCLUSIONS: The results indicate that propolis and plant essential oils appear to be a promising source of antimicrobial agents that may prevent dental caries and other oral infectious diseases.

The c-di-AMP signaling system influences stress tolerance and biofilm formation of Streptococcus mitis.

Streptococcus mitis is a commensal bacterial species of the oral cavity, with the potential for opportunistic pathogenesis. For successful colonization, S. mitis must be able to adhere to surfaces of the oral cavity and survive and adapt to frequently changing environmental conditions. Cyclic-di-AMP (c-di-AMP) is a nucleotide second messenger, involved in the regulation of stress responses and biofilm formation in several bacterial species. Cyclic-di-AMP is produced by diadenylate cyclases and degraded by phosphodiesterases. We have previously shown that in S. mitis, one diadenylate cyclase (CdaA) and at least two phosphodiesterases (Pde1 and Pde2) regulate the intracellular concentration of c-di-AMP. In this study, we utilized S. mitis deletion mutants of cdaA, pde1, and pde2 to analyze the role of c-di-AMP signaling in various stress responses, biofilm formation, and adhesion to eukaryotic cells. Here, we demonstrate that the Δpde1 mutant displayed a tendency toward increased susceptibility to acetic acid at pH 4.0. Deletion of cdaA increases auto-aggregation of S. mitis but reduces biofilm formation on an abiotic surface. These phenotypes are more pronounced under acidic extracellular conditions. Inactivation of pde1 or pde2 reduced the tolerance to ciprofloxacin, and UV radiation and the Δpde1 mutant was more susceptible to Triton X-100, indicating a role for c-di-AMP signaling in responses to DNA damage and cell membrane perturbation. Finally, the Δpde2 mutant displayed a tendency toward a reduced ability to adhere to oral keratinocytes. Taken together, our results indicate an important role for c-di-AMP signaling in cellular processes important for colonization of the mouth.