Streptococcus salivarius K12 in preventing acute otitis media in children
Thesis event information
Date and time of the thesis defence
Place of the thesis defence
Pharmacology Lecture Hall F202, Kontinkangas Campus
Topic of the dissertation
Streptococcus salivarius K12 in preventing acute otitis media in children
Doctoral candidate
Doctor of Medicine Suvi Sarlin
Faculty and unit
University of Oulu Graduate School, Faculty of Medicine, Research Unit of Clinical Medicine
Subject of study
Medicine
Opponent
Professor Terho Heikkinen, University of Turku
Custos
Professor Terhi Ruuska-Loewald, University of Oulu
Streptococcus salivarius K12 probiotic for the prevention of acute otitis media in children
Acute otitis media is the leading reason for antibiotic treatment in children. Young children in day care have particularly frequent respiratory infections and ear infections. New means of preventing acute otitis media are still needed. S. salivarius is a normal bacterium of the human mouth and throat. The K12 strain was originally isolated from the saliva of a healthy child. It produces bacteriocins, antimicrobial peptides that inhibit the growth of other bacteria. The aim of this doctoral thesis was to study whether the probiotic Streptococcus salivarius K12 is suitable for preventing acute otitis media in children, and to investigate the microbes associated with acute otitis media.
In a cohort of 1 096 children in the pediatric emergency room in Oulu University Hospital, 144 purulent middle ear infections were diagnosed. The absolute number of otitis media diagnoses was the highest in children with rhinovirus (41 ear infections among 271 children).
In a randomised clinical trial of 121 children under school age, the thesis showed that oral S. salivarius K12 reduced the nasopharyngeal prevalence of Moraxella, a bacterium that causes acute otitis media, during the probiotic use. S. salivarius K12 did not otherwise disturb or alter the salivary or nasopharyngeal microbiota.
The clinical effectiveness of the K12 probiotic was evaluated in the randomised and double-blind Salli study of 827 children in 50 daycare centers in Oulu. Acute otitis media was much less common than usual during the study because of measures taken during the COVID-19 pandemic. Even after spring 2020, these measures markedly reduced the spread of infections among all children, although daycare centers operated normally. At least one episode of acute otitis media during 6 months occurred in 5.8% of children who received placebo and in 8.2% of children who received S. salivarius K12. S. salivarius K12 was therefore not effective in preventing acute otitis media.
The study shows that all probiotics for children should be carefully evaluated in clinical trials before they are assumed to prevent disease. The study design was logical. The K12 probiotic was chosen because it could specifically affect the oral and pharyngeal microbiota, which is important in the development of acute otitis media. Even so, the preventive approach proved ineffective. The effect of the COVID-19 pandemic on infections was much larger than expected when the study began. This affects the interpretation of the results.
In a cohort of 1 096 children in the pediatric emergency room in Oulu University Hospital, 144 purulent middle ear infections were diagnosed. The absolute number of otitis media diagnoses was the highest in children with rhinovirus (41 ear infections among 271 children).
In a randomised clinical trial of 121 children under school age, the thesis showed that oral S. salivarius K12 reduced the nasopharyngeal prevalence of Moraxella, a bacterium that causes acute otitis media, during the probiotic use. S. salivarius K12 did not otherwise disturb or alter the salivary or nasopharyngeal microbiota.
The clinical effectiveness of the K12 probiotic was evaluated in the randomised and double-blind Salli study of 827 children in 50 daycare centers in Oulu. Acute otitis media was much less common than usual during the study because of measures taken during the COVID-19 pandemic. Even after spring 2020, these measures markedly reduced the spread of infections among all children, although daycare centers operated normally. At least one episode of acute otitis media during 6 months occurred in 5.8% of children who received placebo and in 8.2% of children who received S. salivarius K12. S. salivarius K12 was therefore not effective in preventing acute otitis media.
The study shows that all probiotics for children should be carefully evaluated in clinical trials before they are assumed to prevent disease. The study design was logical. The K12 probiotic was chosen because it could specifically affect the oral and pharyngeal microbiota, which is important in the development of acute otitis media. Even so, the preventive approach proved ineffective. The effect of the COVID-19 pandemic on infections was much larger than expected when the study began. This affects the interpretation of the results.
Created 4.11.2026 | Updated 4.11.2026