Learning Objectives: The objective of this presentation is to discuss the evidence for biofilms and persister cells in the pathophysiology of aggressive cholesteatomas.

Microbial biofilm formation has been observed in human and experimental cholesteatomas. These biofilms occur in the keratin matrix of the cholesteatoma. They are sometimes associated with inflammatory cells, but sometimes devoid of inflammatory cells. The most common organisms found in infected cholesteatomas are Staphylococcus aureus and Pseudomonas aeruginosa. These are well known biofilm forming organisms.

However, recent studies have shown that inoculation of P. aeruginosa mutants devoid of the ability to form biofilms (PA01∆FleQ and others) are inoculated into experimental cholesteatomas, the persistence of infection and the tissue destruction observed are no different than when they are infected with the wild type bacterium (PA01). These studies raise questions about the role of biofilm formation, per se, in the chronicity of infections in aural cholesteatomas.

Recent evidence supports the concept that isolated bacterial cells, termed “persister cells” may be present in infected cholesteatoma in the presence or absence of a biofilm. Persister cells assume a very low metabolic rate and replicate only at minimal levels. These persister cells are highly tolerant to antibiotics, although viable and under the right conditions would begin replicating again and assume their planktonic phenotype.