BASF, a German chemical manufacturing firm, is working on developing a chewing gum that prevents tooth decay(虫歯). The gum, which could be on sale by next year, contains a new strain of the "friendly" bacteria Lactobacillus, a microbe(微生物)found naturally in yogurt. The strain binds to the bacterium which causes tooth decay, causing it to clump(かたまる)together and preventing it from adhering to teeth.