Thirteen strains of gram-positive, catalase-negative, chain-forming cocci isolated from the vestibular mucosa of human oral cavities were compared with other oral streptococcal species. The new strains were unusual in that they formed acid from lactose, from salicin, and usually from cellobiose, but not from mannitol, sorbitol, inulin, or raffinose, and infrequently formed acid from trehalose. They hydrolyzed esculin, urea, and starch but not arginine, formed hydrogen peroxide, and were usually Voges-Proskauer positive. They did not produce extracellular glucan or fructan from sucrose. The strains were compared by analyzing long-chain fatty acids, by determining whole-cell polypeptide patterns by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, and by performing deoxyribonucleic acid (DNA)-DNA hybridizations. They possessed fatty acid profiles with major amounts of hexadecanoic (C16:0) and octadecenoic (C18:1ω7; -vaccenic) acids together with tetradecanoic (C14:0; myristic), hexadecenoic (C16:1; palmitoleic), octadecanoic (C18:0; stearic), octadecenoic (C18:1ω9; oleic), and eicosenoic (C20:1) acids, as shown by capillary gas-liquid chromatography. The sodium dodecyl sulfate-polyacrylamide gel electrophoresis polypeptide patterns of the isolates showed some similarity to the patterns obtained for strains of subsp. , although they were, nevertheless, clearly distinguishable from the latter. DNA-DNA hybridization studies demonstrated that the new strains are more closely related to than to the other species of oral streptococci, but are sufficiently dissimilar to warrant separate species status. The name is proposed. The DNA base composition is 38 to 41 mol% guanine plus cytosine. The type strain is strain MM1 (= NCTC 12166).


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