Biofilm formation by Haemophilus influenzae isolated from adeno-tonsil tissue samples, and its role in recurrent adenotonsillitis

Aim of the present study was to identify bacterial biofilms in tissue samples obtained from paediatric patients undergoing surgical treatment, for chronic and recurrent adeno-tonsillitis, not responding to repeated cycles of selective medical antibiotic and anti-inflammatory treatment and to assay the ability of Haemophilus influenzae strains, most frequently identified in the culture examinations, to grow as biofilm in vitro. Overall, 25 surgical specimens (15 adenoids, 10 tonsils) were examined from the upper respiratory tract, from 15 paediatric patients (mean age 6 years). All patients were affected by recurrent and/or chronic adenoiditis and adenotonsillitis unresponsive to selective antibiotic and anti-inflammatory therapy. Tissues were cultured using conventional methods and subjected to scanning electron microscopy for detection of biofilm. Haemophilus influenzae strains, were cultured on 96-sterile well polystyrene microtitre plates (CELLSTAR-greiner bio-one) and stained with 1% crystal violet to quantify biofilm production. Bacterial cocci attached to the tissue surface and organized in colonies, with a morphology consistent with bacterial coccoid biofilms, were observed in all adenoid (15/15) and in 6/10 tonsil samples. Haemophilus influenzae isolates from 12/25 (48%) of our tissue samples scored a percent transmittance (%Tbloc) > 50, displaying a high capacity to form biofilms (level 4). In conclusion identification of bacterial biofilms in chronic and/or recurrent paediatric upper airway inflammatory processes and the capacity to produce biofilm in vitro, demonstrated by Haemophilus influenzae (the most frequently identified bacteria in our samples), could be related to the aetiopathogenic role of biofilms in chronic inflammatory mucosal reactions and to the resistance of these infections to selective antibiotic therapy.