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Distribution and characterization of hemolytic activity by an oral anaerobe from the Streptococcus milleri group
1Department of Preventive Dentistry, Kagoshima University Dental School, Kagoshima, Japan.
Abstract:
Some oral anaerobes from the Streptococcus milleri strain group were found to secrete human specific hemolytic toxin, which was detected when bacteria were cultured in Todd-Hewitt broth and Brain Heart Infusion broth. The toxin elicited by the Streptococcus intermedius strain was partially fractionated by ammonium sulfate precipitation. Preincubation with glutathione or cysteine showed significant inhibiting effects; however, no effects were seen with dithiothreitol or beta-mercaptoethanol, and cholesterol was a weak inhibitor. Five kinds of protease inhibitor had no effect on the hemolytic activity, and rabbit preimmune and immune sera against the bacterial cells showed weak inhibition at a similar level. Digestion with trypsin, chymotrypsin, proteinase-K, subtilisin and pronase-P brought about a rise in activity, followed by a decrease during long-term incubation. Other enzymes tested showed no effects. Further, the presence of the intermedilysin gene in the portion with hemolytic activity was not identified by polymerase chain reaction.
Insights
Oral bacteria, specifically Streptococcus milleri group strains, produce a human-specific hemolytic toxin. Glutathione and cysteine inhibit this toxin, while protease inhibitors and specific enzymes have varied effects.
Area of Science:
- Microbiology
- Oral biology
- Bacterial toxins
Background:
- The Streptococcus milleri strain group comprises oral commensal bacteria.
- Some strains within this group are known to produce toxins affecting human cells.
Purpose of the Study:
- To investigate the hemolytic toxin secreted by oral anaerobes from the Streptococcus milleri strain group.
- To characterize the properties and identify the source of this human-specific hemolytic toxin.
Main Methods:
- Bacterial cultures in Todd-Hewitt and Brain Heart Infusion broths.
- Partial toxin fractionation using ammonium sulfate precipitation.
- Inhibition assays with various compounds (glutathione, cysteine, dithiothreitol, beta-mercaptoethanol, cholesterol) and protease inhibitors.
- Enzymatic digestion studies and polymerase chain reaction (PCR) for gene identification.
Main Results:
- A human-specific hemolytic toxin was detected from Streptococcus milleri group strains.
- Glutathione and cysteine significantly inhibited hemolytic activity.
- Cholesterol showed weak inhibition; protease inhibitors had no effect.
- Certain proteases initially increased activity before decreasing it; other enzymes were ineffective.
- The intermedilysin gene was not detected in the active toxin fraction via PCR.
Conclusions:
- Oral Streptococcus milleri group strains secrete a human-specific hemolytic toxin.
- The toxin's activity is modulated by specific thiol compounds and proteases.
- Further characterization is needed as the intermedilysin gene was not identified in the active fraction.
