Bacterial Interference IV. Epidemiological Determinants of the Antagonistic Activity of the Normal Throat Flora Against Group A Streptococci

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Abstract
Epidemiological factors, such as age, race, sex and time of culture, that might influence the ability of the normal pharyngeal flora to interfere with growth of group A streptococci were investigated. From March 1974-Feb. 1975, throat swabs were obtained from 952 individuals. Cultures were assayed by an agar overlay procedure for the presence of bacteria capable of inhibiting growth of group A streptococci. The observed inhibition was then determined to be bacteriostatic or bactericidal by use of a broth filtrate technique. Regardless of age, race or sex, subjects were more likely to harbor interfering flora if cultured during March and April, which coincided with the highest prevalence of group A streptococci in the community. Race and sex of subjects appeared not to influence the quantitative or qualitative inhibitory activity of throat flora. Among individuals with interfering flora, the prevalence of bactericidal organisms increased and bacteriostatic organisms decreased with advancing age. Since the presence of bactericidal, and not bacteriostatic, organisms is associated with resistance to colonization of the throat by group A streptococci, this higher prevalence of bactericidal organisms in older individuals suggests that bacterial interference may partially account for the greater resistance of adults than children to streptococcal throat infection.