FleQ, a Transcriptional Activator, Is Required for Biofilm Formation In Vitro But Does Not Alter Virulence in a Cholesteatomas Model.

Hypothesis: Bacterial biofilm formation within cholesteatomas is responsible for increased persistence and tissue destruction and Pseudomonas aeruginosa deficient in biofilm formation (PAO1 ΔfleQ) are less virulent than the parent bacteria.

Background: Infected aural cholesteatomas have been demonstrated to be more destructive than uninfected cholesteatomas and infections are more persistent. The chronicity and persistence of infections within cholesteatomas may be because of the presence of biofilm formation.

Methods: Twenty-seven mutant strains of PAO1 were screened for surface adherence. These strains were also screened for static biofilm formation. The biofilms were quantified by staining with crystal violet. Aural cholesteatomas were then induced in Mongolian gerbils by ligation of the ear canal. At the time of ligation, the ear canals were inoculated with wild-type PAO1 and a biofilm deficient PAO1 ΔfleQ strain of P. aeruginosa. A 7 weeks course of ciprofloxacin (20 mg/kg/day) was started on postoperative day 7. Eight weeks after induction of cholesteatomas, the cholesteatoma size, levels of bone destruction, and levels of bone remodeling were evaluated using microCT imaging.

Results: PAO1 ΔfleQ was identified as a poorly adherent and deficient biofilm forming mutant strain of P. aeruginosa. Infected cholesteatomas had more growth, bone destruction and bone remodeling than uninfected cholesteatomas. However, there was no difference observed between cholesteatomas infected with PAO1 (biofilm competent strain) and PAO1 ΔfleQ (biofilm deficient strain).

Conclusion: We demonstrate that the biofilm phenotype is not an important virulence factor in cholesteatomas infected with P. aeruginosa.