[Significance of normal oral flora, particularly group oral streptococci as defense mechanism against infection in healthy individuals (normal defense mechanism by oral Streptococcus group)].

The alpha-streptococci, consisted of normal oral flora mainly, with inhibitory activity against pathogenic microbes in healthy individuals was investigated by group A Streptococcus (indicator strain 6-22 nonmucoid T-12). Rate of alpha-streptococci with inhibitory activity against group A Streptococcus was increased as aging, and the rate in pre-school children was higher than that in school children. These results suggested that more than 90% of the tested alpha-streptococci with strong inhibitory activities (S. salivarius) against indicator strain had inhibitory activities against group A Streptococcus (mucoid T-6), H. influenzae, S. pneumoniae, group C Streptococcus, and from 40% to 70% of the tested strains had also inhibitory activities against other pathogens. As there were many strains of alpha-streptococci with inhibitory activities against pathogens, that usually detected in the upper respiratory infection, the problem on the strains in the future will explain significance of the defense mechanism against upper respiratory infection and this can be applied clinically.