Summary auto-generated
Researchers describe Streptococcus downei, a new bacterial species isolated from dental plaque of macaque monkeys (Macaca fascicularis). These strains were previously classified as Streptococcus mutans serotype h but are now recognized as a distinct species based on comprehensive molecular and biochemical analyses. Although S. downei resembles S. sobrinus closely, key differences distinguish it: S. downei ferments mannitol but not sorbitol, melibiose, inulin, or raffinose; does not produce hydrogen peroxide; and resists bacitracin. Analysis of cellular components—including protein patterns, long-chain fatty acids (containing a unique cyclopropane acid), and polar lipids—confirmed distinctness. DNA-DNA hybridization studies using S1 nuclease and renaturation rate methods demonstrated significant genetic separation from all other mutans streptococci species. Western blotting revealed unique antigens in S. downei absent from related species. The organism is cariogenic in germfree rats and has a DNA base composition of 41-42 mol% guanine plus cytosine. The type strain is MFe28 (NCTC 11391T), isolated from Downe, Kent, England.
Key findings
- S. downei is a new streptococcal species distinct from S. mutans serotype h and S. sobrinus, supported by biochemical, immunological, and DNA-DNA hybridization data.
- S. downei ferments mannitol but not sorbitol, melibiose, inulin, or raffinose, and does not produce hydrogen peroxide, distinguishing it from related species.
- S. downei contains a unique cyclopropane acid (cis-9,10-methyleneoctadecanoic acid) in its long-chain fatty acid composition, absent from S. sobrinus.
- The organism is cariogenic in monoassociated germfree rats, indicating pathogenic potential in dental disease.
- DNA-DNA hybridization showed S. downei shares only 40-50% homology with S. sobrinus and less than 10% with other mutans streptococci species.
This summary was generated automatically from the article PDF and is not part of the original publication. Refer to the PDF for the authoritative text.
Abstract
Strains of streptococci originally isolated from the dental plaque of monkeys (Macaca fascicularis) and designated as Streptococcus mutans serotype h were compared with the other species of the mutans streptococcus group. Despite the close resemblance noted previously between these strains and Streptococcus sobrinus, closer examination revealed several important differences. Strains of serotype h ferment mannitol but not sorbitol, melibiose, inulin, or raffinose, do not produce hydrogen peroxide, and are unable to grow in the presence of bacitracin at 2 units per ml. They exhibit a distinct polypeptide pattern by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and possess several antigens absent from S. sobrinus as revealed by Western blotting (immunoblotting). Virtually identical polar lipid patterns were observed by two-dimensional thin-layer chromatography for both serotype h strains and S. sobrinus, although on the basis of long-chain fatty acid analysis by capillary gas-liquid chromatography, the former could be distinguished by the presence of a peak tentatively identified as cyclopropane acid (cis-9, 10-methyleneoctadecanoate (ΔC 19:0). Deoxyribonucleic acid (DNA)-DNA hybridization studies by both the S1 nuclease and renaturation rate methods showed that serotype h strains differ from S. mutans, S. sobrinus, Streptococcus cricetus, Streptococcus rattus, Streptococcus ferus, and Streptococcus macacae. On the basis of these data, we believe that S. mutans serotype h strains represent a distinct species for which the name Streptococcus downei is proposed. The DNA base composition is 41 to 42 moles percent guanine plus cytosine. The type strain is strain MFe28 (NCTC 11391T), which is cariogenic in monoassociated germfree rats.