A method for the treatment and prevention of dental caries and periodontal diseases using bacteriophages and phage-encoded anti-bacterial enzymes to inhibit establishment of bacteria in the oral cavity is provided. Also provided are methods for studying the cell wall of an oral bacterium, a method for preventing spoilage of perishable items and a method for removing dextrans from surfaces utilized in sugar manufacture. Purified enzymes and the isolated DNA fragments encoding them are also provided.