Prospective observational study of adenoidal biofilms in a paediatric population and its clinical implications

INTRODUCTION: Adenoids are nasopharyngeal lymphoid tissue with a relevant role in host defence against infection of upper respiratory tract. Nevertheless, adenoids are also a reservoir of microorganisms that can cause infections of upper respiratory tract and otitis particularly in children. OBJECTIVE: Evaluate and compare the association between biofilm assembly on adenoids and the incidence of recurrent infections in a paediatric population submitted to adenoidectomy by either infectious or non-infectious indication. METHODS: Scanning electron microscopy was used to assess biofilms on adenoid surface; biofilm assembly in vitro was monitored by crystal violet assay; antibiotic susceptibility was assessed following EUCAST guidelines; Hinfluenzae capsular typing was performed by PCR. RESULTS: Biofilms were present in 27.4% of adenoid samples and no statistical difference was found between infectious and non-infectious groups. In vitro, the most clinically relevant bacteria, H.influenzae, S.aureus, S.pyogenes, S.pneumoniae and M.catarrhalis, were mostly moderate biofilm assemblers (71.7%). 55.3% of these bacteria were intermediate/resistant to at least one of the tested antibiotics. No association was found between the ability to assemble biofilms in vitro and the presence of biofilms on adenoids nor antibiotic resistance. All H.influenzae were characterized as non-typeable. CONCLUSION: The presence of biofilms on adenoid surface was independent from clinical sample background. Bacterial ability to assemble biofilms in vitro cannot be used to predict biofilm assembly in vivo. The lack of correlation between biofilm formation and infectious respiratory diseases found contributes to question the relevance of biofilms on the pathogenesis of infectious diseases.