Abstract
Distribution of bacteria which produce enzyme capable of lysing Str. mutans E49 strain in human dental plaques was investigated on adults of age 20 to 22. The activity of the enzyme (MLE) produced by an isolated strain (FDC-63) was also investigated. The results obtained are summarized as follows. 1. MLE producing bacteria were detected in 43 samples (37.1%) out of 116 samples of dental plaques obtained from adults of age 20 to 22. 2. Twenty four samples had MLE producing bacteria at the rate of over 5% of total number of bacteria in each sample. 3. The 40 strains isolated were composed of 92.5% of Gram positive cocci, 2.5% of Gram negative cocci and 5% of Gram positive rods. 4. Most of the isolates (84.6%) showed lytic activity against living cells of E49 on GAM agar plates. 5. The MLE produced by FDC-63 had lytic activity against both living and heat killed cells of E49 under aerobic or anaerobic condition. 6. The activity of the MLE was rather weak against purified cell walls of E49. 7. Optimal pH in the activity of the MLE was 6.0 and optimal temperature 37℃. The activity of the MLE was lost by heating at 60℃ for 60 min. 8. FDC-63 was identified as Streptococcus milleri.
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