Bacteriology of the human tonsils
The tonsillar crypt microbiota associated with health and recurrent tonsillitis
Tonsillitis is a common infection of the palatine tonsils mostly occurring in children and young adults.  Especially recurrent tonsillitis is a clinical problem and many patients may ultimately undergo tonsillectomy. While a single microbial species may cause acute tonsillitis, it has been suggested that recurrent tonsillitis is a consequence of a polymicrobial infection or a shift in the microbial composition. In this study we compared the bacterial diversity within the crypts of the palatine tonsils of children and adults affected by recurrent tonsillitis with that of healthy adults and children with tonsillar hyperplasia. The study employed a high-throughput multiplexed 16S rRNA gene pyrosequencing approach combined with a novel strategy that enabled us to identify a significant part of the microbiota to species level.   Our results demonstrate that the microbiota of the tonsillar crypts by the age of 2-4 years already has reached the same degree of overall complexity as found in adults, but still shows striking differences. Bacteria that were almost exclusively detected in children were Haemophilus influenzae, Neisseria species, and S. pneumoniae.  Obligate anaerobes like Porphyromonas, Prevotella, and Fusobacterium were abundantly present in children, but the diversity of Porphyromonas and Prevotella species was larger in adults and included species that are considered putative pathogens in periodontal diseases i.e. P. gingivalis, P. endodontalis, and Tannerella forsythia. A core microbiome of relative few, but abundant genera were found in all samples regardless of age or health status. Unifrac analysis showed that recurrent tonsillitis is associated with a shift in the bacterial composition in the tonsillar crypts. Particularly, F. necrophorum was associated with recurrent tonsillitis in adults, but also S. intermedius and P. melaninogenica/P. histicola were correlated to recurrent tonsillitis in adults, whereas species traditionally associated with acute tonsillitis like S. pyogenes, S. dysgalactiae subsp. equisimilis and S. aureus, were found in very low proportions. The findings suggest that interactions within consortia of taxa play a role in recurrent tonsillitis as assumed in other polymicrobial infections. Improved techniques with a higher resolution have to be developed for microbial diversity studies before this hypothesis can be fully explored.