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Concept: Streptococcus mitis


Genomic, taxonomic and biochemical studies were performed on two strains of alpha-haemolytic streptococci that showed to be clustered with major members of the Streptococcus mitis group. These Gram-positive strains were isolated from tooth surfaces of caries-free humans and show the classical spherical-shape of streptococcal species growing in chains. Sequence analysis from concatenated 16S and 23S rDNA, and sodA genes showed that these strains belonged to the Mitis group, but both of them cluster into a new phylogenetic branch. The genomes of these two isolates were sequenced, and whole-genome Average Nucleotide Identity (ANI) demonstrated that these strains significantly differ from any streptococcal species, showing ANI values under 91% even when compared to their phylogenetically closest species such as Streptococcus oralis and Streptococcus mitis. Biochemically, the two isolates also showed distinct metabolic features relative to close species, like an ╬▒-galactosidase activity. From the results of the present study, the name Streptococcus dentisani sp. nov. is proposed for these new couple of strains deposited in open collection at the Spanish Type Culture Collection (CECT) and Leibniz Institute DSMZ-German Collection of Microorganism and Cell Cultures (DSMZ); being respectively identified as Streptococcus dentisani Str. 7746 (CECT 8313, DSM 27089) and Streptococcus dentisani Str. 7747 (CECT 8312T, DSM 27088T).

Concepts: Gene, Bacteria, Organism, Streptococcus, Gram positive bacteria, Streptococcaceae, Streptococcus oralis, Streptococcus mitis


Viridans group streptococci (VGS) are a major cause of bacteraemia in neutropenic cancer patients, particularly those receiving fluoroquinolone prophylaxis. In this study, we sought to understand the molecular basis for fluoroquinolone resistance in VGS causing bacteraemia in cancer patients by assigning 115 VGS bloodstream isolates to specific species using multilocus sequence analysis (MLSA), by sequencing the quinolone resistance-determining regions (QRDRs) of gyrA, gyrB, parC and parE, and by testing strain susceptibility to various fluoroquinolones. Non-susceptibility to one or more fluoroquinolones was observed for 78% of isolates, however only 68.7% of patients were receiving fluoroquinolone prophylaxis. All but one of the determinative QRDR polymorphisms occurred in GyrA or ParC, yet the pattern of determinative QRDR polymorphisms was significantly associated with the fluoroquinolone prophylaxis received. By combining MLSA and QRDR data, multiple patients infected with genetically indistinguishable fluoroquinolone-resistant Streptococcus mitis or Streptococcus oralis strains were discovered. Together these data delineate the molecular mechanisms of fluoroquinolone resistance in VGS isolates causing bacteraemia and suggest possible transmission of fluoroquinolone-resistant S. mitis and S. oralis isolates among cancer patients.

Concepts: Streptococcus, Gram positive bacteria, Streptococcaceae, Group A streptococcal infection, Quinolone, Streptococcus viridans, Streptococcus oralis, Streptococcus mitis


To report a case of hyperacute Streptococcus mitis endophthalmitis after intravitreal ranibizumab resulting in occlusive vasculitis.

Concepts: Streptococcus, Streptococcus mitis


Among viridans group streptococcal infective endocarditis (IE), the Streptococcus mitis group is the most common aetiological organism. Treatment of IE caused by the S. mitis group is challenging due to the high frequency of ╬▓-lactam resistance, drug allergy and intolerability of mainstay antimicrobial agents such as vancomycin or gentamicin. Daptomycin has been suggested as an alternative therapeutic option in these scenarios based on its excellent susceptibility profile against S. mitis group strains. However, the propensity of many S. mitis group strains to rapidly evolve stable, high-level daptomycin resistance potentially limits this approach.

Concepts: Bacteria, Streptococcus, Infective endocarditis, Enterococcus, Gram positive bacteria, Antimicrobial, Streptococcaceae, Streptococcus mitis


Streptococcus mitis group is the most common cause of infective endocarditis among the viridans group streptococci. It has a propensity to be ╬▓-lactam-resistant, as well as to rapidly develop high-level and durable resistance to daptomycin. We compared a parental, daptomycin-susceptible (DAP-S) S. mitis/oralis strain and its daptomycin-resistant (DAP-R) variant in an experimental endocarditis model in terms of: i) their relative fitness in multiple target organs in this model (vegetations; kidneys; spleen) when animals were challenged either individually vs. in a co-infection strategy; and ii) their survivability during therapy with daptomycin + gentamicin (an in vitro combination synergistic against the parental strain). The DAP-R variant was initially isolated from the cardiac vegetations of animals with experimental endocarditis caused by the parental DAP-S strain following treatment with daptomycin. The parental and DAP-R variant were comparably virulent, when animals were individually challenged. In contrast, in the co-infection model without daptomycin therapy, at both a 10(6) and 10(7) CFU challenge inoculum, the parental strain out-competed the DAP-R variant in all target organs, especially kidneys and spleen. When the co-infection endocarditis model was treated with DAP + gentamicin, the DAP-S strain was completely eliminated, while the DAP-R variant persisted in all target tissues. These data underscore that the acquisition of DAP-R in S. mitis/oralis does come at an intrinsic fitness cost, although this resistance phenotype is completely protective against therapy with a potentially synergistic DAP regimen.

Concepts: HIV, Evolution, Streptococcus, Infective endocarditis, Virology, Streptococcaceae, Group A streptococcal infection, Streptococcus mitis


The discovery that Streptococcus pneumoniae uses a competence-stimulating peptide (CSP) to induce competence for natural transformation, and that other species of the mitis and the anginosus streptococcal groups use a similar system, has expanded the tools to explore gene function and regulatory pathways in streptococci. Two other classes of pheromones have been discovered since then, comprising the bacteriocin-inducing peptide class found in Streptococcus mutans (also named CSP, although different from the former) and the SigX-inducing peptides (XIP), in the mutans, salivarius, bovis, and pyogenes groups of streptococci. The three classes of peptide pheromones can be ordered from peptide synthesis services at affordable prices, and used in transformation assays to obtain competent cultures consistently at levels usually higher than those achieved during spontaneous competence. In this chapter, we present protocols for natural transformation of oral streptococci that are based on the use of synthetic pheromones, with examples of conditions optimized for transformation of S. mutans and Streptococcus mitis.

Concepts: Streptococcus pneumoniae, Streptococcus pyogenes, Streptococcus, Gram positive bacteria, Streptococcaceae, Streptococcus mutans, Streptococcus viridans, Streptococcus mitis



Streptococcus mitisfrequently causes invasive infections in neutropenic cancer patients, with a subset of patients developing viridans group streptococcal (VGS) shock syndrome. We report here the first complete genome sequence ofS. mitisstrain SVGS_061, which caused VGS shock syndrome, to help elucidate the pathogenesis of severe VGS infection.

Concepts: Immune system, Bacteria, Virus, Genome, Streptococcus, Set, Streptococcaceae, Streptococcus mitis


Streptococcus tigurinus is a newly described member of the Streptococcus mitis group. Due to the difficulty in distinguishing viridans group streptococci (VGS) by phenotype, analysis of 16S rRNA sequences is necessary for accurate identification of most species. Through a laboratory policy of analyzing all clinically significant isolates from the VGS group by16S rRNA gene sequencing, we identified 14 S. tigurinus isolates from 11 patients. The Vitek 2 system most commonly gave an “excellent” rating to an incorrect identification (e.g. Streptococcus mitis), as did MALDI-TOF MS (e.g. S. oralis). S. tigurinus strains were recovered from numerous body sites including the blood, peritoneal fluid, bone, synovial fluid, a perianal abscess and an arm wound. Retrospective chart review indicated that most isolates were clinically significant with bacteremia (5), soft tissue infections (3) osteomyelitis (2), infected joint prosthesis (2) and peritonitis (2) being the most common, thus expanding the spectrum of disease associated with S. tigurinus.

Concepts: Ribosomal RNA, Infection, Streptococcus, 16S ribosomal RNA, 30S, Streptococcaceae, Group A streptococcal infection, Streptococcus mitis


Septic arthritis of the pubic symphisis is distinguished from osteitis pubis by positive cultures. The symptoms, physical examination and laboratory findings of these two conditions are comparable. We present a case of 57-year-old woman with septic arthritis of pubic symphisis caused by Streptococcus mitis, a commensal oral flora that belongs to viridans group streptococci, which normally reside in the oral cavity, the gastrointestinal and the urogenital tract.

Concepts: Gut flora, Streptococcus, Pelvis, Pubic symphysis, Pubis, Streptococcaceae, Streptococcus mitis, Osteitis pubis