The answer is lysozyme. lysozyme, also known as Muramidase or n-acetylmuramidase glycanhydrolase, is an antimicrobial enzyme produced by animals which forms part of the innate immune system. it catalyses the hydrolysis of the beta linkages between n-acetylmuramic acid and n-acetyl-D-glucosamine residues in a peptidoglycan Of bacteria. also it interacts with antibodies and T-cell receptors. reduced lysozyme level has been associated with bronchopulmonary dysplasia (formerly chronic lung disease of infancy) in newborn. the first chemical synthesis of a lysozyme protein was achieved by Steve Kent at the university of Chicago. lysozyme is a commonly used enzyme for lysing gram positive bacteria . it was the first enzyme structure to be solved via X-ray diffraction .hope it will help you.

Some Nitrates and Peroxides are present in our Saliva, which can kill bacteria. However, main bacterial destruction takes place in our stomach, due to HCl.