Pseudomonas aeruginosa adherence to external auditory canal epithelium

Pseudomonas aeruginosa is an important causative agent for external otitis. The specific bacterium-host reaction has not been investigated. It is therefore unknown whether adhesion of the external otitis strain to the external auditory canal epithelium is increased compared with strains isolated from other infections.

A cohort study was designed to outline adhesion of P aeruginosa to the external auditory canal epithelium, cultured in vitro, of the guinea pig. Factors important for pathogenesis were also studied.

Pseudomonas aeruginosa strains from nonhospitalized patients were collected consecutively at the bacteriological laboratories at Karolinska Hospital, Stockholm, and Huddinge Hospital, Huddinge, Sweden. External otitis strains were compared with strains from leg ulcers, urinary tract infections, and cystic fibrosis.

Adhesion to the external auditory canal epithelium cultured in vitro was measured and compared groupwise with the mean profile of pathogenic factors.

Adhesion to the epithelium was significantly increased for external otitis strains. These strains also had a significantly increased deoxyribonuclease production and a significantly decreased production of pyocyanin and alginate.

The significantly increased ability of P aeruginosa, isolated from external otitis, to adhere to external auditory canal epithelium was combined with a significant production of pathogenic factors. The P aeruginosa that causes external otitis could therefore be considered a particular phenotype. The enzyme profile for external otitis strains was similar to that of the control groups except for the strains from cystic fibrosis. Adhesion to guinea pig vs human epithelium must be compared, and the effects of extracellular proteins on adhesion should be studied to further understand how P aeruginosa adheres to the external auditory canal.