Analysis of defense mechanisms against bacterial infection by oral streptococcus in normal flora.

The incidence of oral alpha-streptococci with inhibitory activity against pathogens as a defense mechanism in the oral cavity was investigated in healthy individuals. Inhibitory strains were isolated from tonsil, tongue, cheek, saliva and dental plaque, and the detection rate of these strains isolated from tonsil was the highest. These results suggested that tonsillar flora is most important as a defense mechanism of the oral cavity. With respect to the effects of antibiotics against inhibitory alpha-streptococci, minimal inhibitory concentration of 90% of cells (MIC90) of PCG, ABPC, CCL, CFIX and EM against inhibitory alpha-streptococci, and relative detection rates of inhibitory alpha-streptococci before and after antimicrobial therapy were investigated. MIC90s of all antibiotics against these strains were low and sensitive to antibiotics tested. However, in vivo, detection rates of these strains before and after therapy did not differ significantly. Therefore, inhibitory strains were not affected by antibiotics as their MIC90 were low during short term medication.