Studies on the Antibacterial Factors of Human Saliva

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Abstract
To amplify previous evidence that human saliva contained > 1 antibacterial principle and to indicate the nature of such agents centrifuged, unstimulated saliva was subjected to various treatments before carrying out "well" tests of its activity against 15 spp. of susceptible bacteria. The agent effective against Micrococcus lysodeikticus, Sarcina lutea, and Bacillus megatherium differed from that acting upon Staphylococcus aureus, Streptococcus hemolyticus, Lactobacillus acidophilus, Bacillus subtilis, Eberthella typhosa, Salmonella paratyphi, S. schottmuelleri, Proteus morganii, Shigella paradysenteriae, Escherichia coli, Proteus vulgaris, and Pseudomonas aeruginosa. The former agent was removed by Berkefeld-N filtration, survived heating at 75[degree] for 5 min., was destroyed by u.v. radiation or by storage at 37[degree] for 24 hrs., was precipitated by acetone but not by acetic acid. The agent effective against the other group of organisms passed the Berkefeld filter, was destroyed by heating at 75[degree], was unaffected by u.-v. radiation and storage. It was not precipitated by acetone but was by acetic acid. Neither was destroyed by freezing and thawing. Both were adsorbed by Kaolin but not by charcoal. Adsorption on bacteria removed the agent effective against organisms of other groups but did not remove the activity against homologous organisms. Attempts at concentration and purification were unsuccessful. It was not possible to find any relationship between the potency of either antibacterial factor in the saliva and the age of the patient, the rate of salivary secretion, number of epithelial cells, leucocytes, total bacteria (hemocytometer count), total viable bacteria (colony count), numbers of starch-hydrolizing bacteria, content of N, non-protein N, total solids, total organic material, catalase, ptyalin, neutralizing powers, and total inorganic and organic buffering capacities of saliva. Comparative tests of the effect of the antibacterial factors in "well" tests and in plate counts indicated that the counting method was more sensitive with the 1st group of organisms, but that this was not true of the 2d group, the difference in the mode of action apparently being related to the rate at which the bacteria were killed. The work confirms the fact that saliva exerts antibacterial effects on a wide variety of organisms and establishes the existence of at least 2 distinct antibacterial factors. One of these resembles lyso-zyme, but the other is apparently distinct from it.

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