The present invention provides an enzyme with lytic activity against cariogenic bacteria and a means for treating and preventing tooth decay using the enzyme. The enzyme provided by the present invention is a lytic enzyme produced by Streptococcus mutans and has a substrate specificity for lysing selectively Streptococcus mutans and Streptococcus sobrinus. Therefore, application of the enzyme enables to remove selectively cariogenic bacteria or to decrease the number of cariogenic bacteria inside oral cavity, and may exert preventive effect against tooth caries.
