Evidence for microbial biofilms in cholesteatomas

Background: Sessile bacteria within biofilms are highly resistant to eradication by antimicrobial agents. Previously, we have shown that the most common organisms cultured from experimentally induced cholesteatomas are biofilm formers. Additionally, the keratin "matrix" of a cholesteatoma is an ideal environment for the support of biofilm formation. Objective: To determine if microbial biofilms occur within the keratin matrix of infected cholesteatomas. Design: We evaluated the histomorphologic characteristics of 24 human and 22 experimental cholesteatomas for evidence of biofilm. formation using light and transmission electron microscopy. Subjects: Human tissues were collected during surgical eradication of existing cholesteatomas. Twenty-two gerbil cholesteatomas were either spontaneously occurring or induced by external auditory canal ligation and harvested several months later. Results: Gram-positive and gram-negative bacteria were seen within acellular deposits among the keratin accumulations in 21 of 22 gerbil and 16 of 24 human cholesteatomas. Regions of accumulated bacteria possessed the ultrastructural appearance of typical amorphous polysaccharide biofilm matrix. Conclusions: There is strong anatomic evidence for the presence of bacterial biofilms in experimental and human cholesteatomas. The existence of bacterial biofilms within cholesteatomas may explain the clinical characteristics of infected cholesteatomas, that is, persistence and recurrence of infection, with surgical eradication being the only effective treatment.