PSEUDOMONAS-AERUGINOSA IN OTITIS-EXTERNA - A PARTICULAR VARIETY OF THE BACTERIA

Background: Pseudomonas aeruginosa rarely affects the epithelium in he althy persons except for the external ear canal, raising the possibili ty that P aeruginosa in otitis externa is a specific variety that disp lays particular characteristics. Design: A cohort study was designed t o outline distinct characteristics of P aeruginosa in otitis externa c ompared with P aeruginosa in other infections. The study period was Oc tober 1, 1994, to March 27, 1995. Patients: Isolates of P aeruginosa f rom nonhospitalized patients were collected at the bacteriological lab oratory at Karolinska Hospital, Stockholm, Sweden; there were 53 strai ns of P aeruginosa isolated from otitis externa and 59 strains of P ae ruginosa from varicose ulcers and urinary tract infections. Methods: P seudomonas aeruginosa was characterized by pigmentation, growth habits , production of mucoid, and biochemical characteristics. Results: Pseu domonas aeruginosa in otitis externa produced less pyocyanin and less urease and exhibited no mucoid-producing strains. Conclusions: Pseudom onas aeruginosa in otitis externa displayed fewer of the usual biochem ical features of the species than did the strains isolated from other infections. Some of these features, such as the production of pyocyani n, are influenced by nutritional factors; strains found in otitis exte rna probably represent the type of strains present in the natural habi tat in water, as opposed to the strains that have adapted to the envir onment of other human infections. Increased knowledge of the character istics of the strains found in otitis externa is important in understa nding the pathogenesis of the disease and why P aeruginosa is the domi nant infectious agent in otitis externa.