Enocin: an antibiotic produced by Streptococcus salivarius that may contribute to protection against infections due to group A streptococci.

Clinical studies have indicated that certain constituents of the normal throat flora may play a role in resistance to group A streptococcal infections. Strains of Streptococcus salivarius were among the most active components of this protective flora. The present studies were designed to determine the mechanism responsible for the antagonism of group A streptococci by S. Salivarius. Cell-free filtrates made at the end of the logarithmic growth phase of S. salivarius inhibited the growth of group A streptococci. The only other organisms susceptible to inhibition by these filtrates were those that require exogenous pantothenate, as group A streptococci do. The activity of filtrates was primarily bacteriostatic and could be specifically reversed by pantothenate. Activity was not due to a simple depletion of the vitamin but rather to the presence of a substance that interfered with the utilization of pantothenate. This substance, given the name enocin, was heat labile but was unaffected by proteolytic enzymes. Thus, strains of S. salivarius that appear to enhance the resistance of certain individuals to streptococcal infection may exert their protective effect through in situ production of the antibiotic enocin.