Inhibitory substances produced by Streptococcus salivarius and colonization of the upper respiratory tract with group...

It has been proposed that inhibitory substances produced by viridans streptococci colonizing the upper respiratory tract aid in eradication of established group A streptococcal colonization of that site. We studied the prevalence of inhibitory-substance producing strains of Streptococcus salivarius in throat cultures from three groups of children: 16 children with persistently positive throat cultures for group A streptococci despite receiving recommended therapeutic courses of antibiotics (group I), 26 children from whom group A streptococci were eradicated from the upper respiratory tract by antibiotic therapy (group II), and 18 children who never harboured group A streptococci in their upper respiratory tract during the study period (group III). An in vitro deferred antagonism method was employed to detect inhibitory substances; 5233 strains of S. salivarius were examined. Strains of S. salivarius producing inhibitory substances were isolated from 76-88% of the children in each group on at least one occasion. However, only a small percentage of subjects in each group harboured strains producing these substances in every throat culture. The mean total percentage of S. salivarius strains producing inhibitory substances was 21.8% in children in group I, 22.4% in children in group II, and 16.4% in children in group III; these percentages were not statistically different (P greater than 0.1). In this study, we could not confirm a significant role for inhibitory substances produced by S. salivarius in the eradication of group A streptococci from the upper respiratory tract of colonized individuals.