Lytic Ability of Exo-enzyme from Streptococcus mutans AL7-1 Strain against Living Cells of Streptococci

P(論文)An exo-enzyme produced by the oral bacterium Streptococcus (Str.) mutans strain AL7-1 that lysed heat-killed cells of Str. sanguis ATCC 10558 was examined for its lytic ability against living cells of stock cultures of streptococci and of the oral isolates of Str. sanguis from the dental plaques of infants. This exo-enzyme showed a clear decrease in OD of living cell suspensions of 4 hr-culture of Str.sanguis ATCC 10558 but in no other streptococcal species. In the reaction mixture, the initially gram positive long-chained cocci were found to have been converted to gram negative, short-chained cocci. It is evident that the decrease in OD of living cell suspension depends on the action of a lytic enzyme, because, this dissolves cell walls of Str. sanguis, in addition its strength is inactivated by heat treatment, and at the same time this enzyme does not contain an activity of bacteriocins. This enzyme showed a fairly good lytic ability against living cells of six out of seven strains of Str.sanguis isolated from the same oral cavity from which Str.mutans AL7-1 was isolated. Furthermore, 43(31%) out of 141 strains of Str.sanguis isolated from dental plaques of 20 infants show a susceptibility to this exo-enzyme similar to or higher than Str.sanguis ATCC 10558. From the above results, if this exo-enzyme is produced from Str.mutans in dental plaques in vivo, it seems would be possible that it may take part in the decrease of S tr. sanguis.departmental bulletin pape