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Description of two morphotypes of Peptostreptococcus micros
P J van Dalen1, T J van Steenbergen, M M Cowan
1Department of Oral Microbiology, Academic Centre for Dentistry Amsterdam, The Netherlands.
Abstract:
Peptostreptococcus micros is often isolated from abscesses in several parts of the human body. The oral cavity is considered the natural habitat for the species, which has been implicated as a periodontal pathogen. In plaque samples from periodontitis patients we observed the presence of a rough morphotype of P. micros in addition to the previously recognized smooth morphotype. The rough morphotype has not been described previously. Both morphotypes are frequently isolated simultaneously from the same patient. In this paper strains of both morphotypes are described. The smooth morphotype, represented by the type strain, grew as small, dome-shaped, bright white, nonhemolytic colonies. The rough morphotype grew as equally white dry colonies which were hemolytic and had wrinkled edges. DNA-DNA reassociation studies revealed homology at the species level between the two morphotypes; in addition, no differences in physiological characteristics were observed when the organisms were tested with API-32A and API-ZYM kits. The rough cells had long, thin fibrillar structures outside the cell envelope when they were stained negatively for electron microscopy. In the smooth morphotype these structures were not present. The sodium dodecyl sulfate-polyacrylamide gel electrophoresis profiles of whole-cell extracts were different for the two morphotypes. In xylene-water phase partition studies, the smooth morphotype was found to be hydrophobic, whereas the rough morphotype was found to be relatively hydrophilic. The distinct morphotypes were stable on blood agar; however, the rough morphotype changed to a nonfibrillar type with a smooth colony morphology after repeated subculturing in broth.
Insights
A newly identified rough morphotype of Peptostreptococcus micros, a periodontal pathogen, was discovered alongside the smooth type. Both morphotypes share genetic homology but exhibit distinct surface structures and cell surface properties.
Area of Science:
- Microbiology
- Oral Health
- Periodontology
Background:
- Peptostreptococcus micros is a known oral bacterium implicated in periodontal disease.
- This species is frequently isolated from human abscesses.
- A novel rough morphotype of P. micros was observed in periodontitis plaque samples.
Purpose of the Study:
- To describe and characterize the previously undescribed rough morphotype of P. micros.
- To compare the rough and smooth morphotypes of P. micros.
- To investigate the genetic and phenotypic differences between the two morphotypes.
Main Methods:
- Isolation and culturing of smooth and rough morphotypes.
- DNA-DNA reassociation studies for genetic homology.
- Physiological characterization using API-32A and API-ZYM kits.
- Electron microscopy for cell surface structure analysis.
- Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) for protein profiling.
- Xylene-water phase partition for cell surface hydrophilicity/hydrophobicity assessment.
Main Results:
- Both smooth and rough morphotypes showed high DNA-DNA homology, confirming they belong to the same species.
- Distinct colony morphologies were observed: smooth (small, dome-shaped, nonhemolytic) and rough (dry, hemolytic, wrinkled edges).
- Rough morphotype cells possessed external fibrillar structures, absent in the smooth morphotype.
- SDS-PAGE profiles differed between morphotypes.
- Smooth morphotype was hydrophobic, while the rough morphotype was relatively hydrophilic.
- Rough morphotype stability was observed on blood agar, but it transitioned to a smooth, nonfibrillar type upon repeated broth subculturing.
Conclusions:
- Peptostreptococcus micros exhibits distinct stable morphotypes (smooth and rough) with significant phenotypic differences.
- The rough morphotype is characterized by fibrillar surface structures and altered cell surface properties.
- These findings contribute to understanding the heterogeneity within P. micros populations and their role in periodontal disease.