Extracellular esterases of streptococci and the distribution of specific antibodies in human sera of various age groups.

Most of the streptococci representative of Lancefield Groups A through O produced an extracellular carboxylic acid esterase active against β-naphthyl acetate. No esterase activity was found in organisms of Groups D and N. Group K strains were not examined. The esterases could be differentiated into five distinct immunologic types based on reactions of identity or non-identity in immunodiffusion with normal adult human sera. A few strains produced esterases that did not react with the human sera in these immunologic tests. The distribution of antibodies to the five esterases was determined in the sera of infants, children and adults. Antibodies to the esterase E-IV, obtained from animal Group C strains, were rarely found. Antibodies to the other four esterases, E-I, E-II, E-III, and E-V, were present in the sera of newborns as frequently as they were in adults. Presumably these were antibodies obtained from the mother by placental transfer. Infants produced antibodies to these esterases with increasing frequency after the first year of age. The incidence of antibodies to these esterases in children in the 9- and 10-year-old age groups was similar to that observed in adults. The occurrence of antibodies to esterases E-III and E-V obtained from Group B and Group L streptococci, respectively, is contrary to present epidemiologic data pertaining to human infection with these organisms. A cross-reacting antigenic stimulus has not been demonstrated.