Bacterial Interference. II. Role of the Normal Throat Flora in Prevention of Colonization by Group A Streptococcus

A prospective study was designed to determine the possible role of the normal flora of the throat in resistance to infection with group A Streptococcus. Throat cultures were obtained from 40–50 children in a closed population for each of 20 consecutive weeks. The ability of the normal flora to inhibit the growth of group A Streptococcus was determined by agar overlay and broth filtrate techniques. During the study, 38 of the children became colonized with group A streptococci. Cultures from children who did not become colonized showed significantly greater inhibitory activity and more frequently contained bactericidal organisms than cultures from children who subsequently acquired group A Streptococcus. Cultures taken after children had been colonized showed more inhibitory activity than cultures taken before or during colonization.