Pseudomonas aeruginosa in otitis externa. A particular variety of the bacteria?
J. Sundstrom, K. Jacobson, E. Munck-Wikland and S. Ringertz
Department of Clinical Microbiology, Karolinska Hospital, Stockholm, Sweden.
BACKGROUND: Pseudomonas aeruginosa rarely affects the epithelium in healthy
persons except for the external ear canal, raising the possibility that P
aeruginosa in otitis externa is a specific variety that displays particular
characteristics. DESIGN: A cohort study was designed to outline distinct
characteristics of P aeruginosa in otitis externa compared with P
aeruginosa in other infections. The study period was October 1, 1994, to
March 27, 1995. PATIENTS: Isolates of P aeruginosa from nonhospitalized
patients were collected at the bacteriological laboratory at Karolinska
Hospital, Stockholm, Sweden; there were 53 strains of P aeruginosa isolated
from otitis externa and 59 strains of P aeruginosa from varicose ulcers and
urinary tract infections. METHODS: Pseudomonas aeruginosa was characterized
by pigmentation, growth habits, production of mucoid, and biochemical
characteristics. RESULTS: Pseudomonas aeruginosa in otitis externa produced
less pyocyanin and less urease and exhibited no mucoid-producing strains.
CONCLUSIONS: Pseudomonas aeruginosa in otitis externa displayed fewer of
the usual biochemical features of the species than did the strains isolated
from other infections. Some of these features, such as the production of
pyocyanin, are influenced by nutritional factors; strains found in otitis
externa probably represent the type of strains present in the natural
habitat in water, as opposed to the strains that have adapted to the
environment of other human infections. Increased knowledge of the
characteristics of the strains found in otitis externa is important in
understanding the pathogenesis of the disease and why P aeruginosa is the
dominant infectious agent in otitis externa.