A bacteriological study of otitis media with effusion. Concurrent coagulase-negative staphylococcal infections in the middle ear.

We investigated the bacteriology of 50 chronic middle ear effusions from 30 children (mean age, 5 years 4 months) and compared this with the microorganisms present in the external ear canals and adenoids of each patient to distinguish pure middle ear bacteria from probable contaminations. Coagulase-negative staphylococci (CS), formerly considered to be non-pathogens, were the most frequently isolated bacteria in the middle ear effusions and were followed in incidence by alpha-hemolytic streptococci and group D streptococci. CS were found in 24% of all effusions and in 44% of the infected effusions. Most of the CS strains belonged to the species of Staphylococcus epidermidis. Although the majority of CS isolated from the middle ear effusions studied proved not to be contaminants, the populations of CS in the middle ear and external ear canal showed similar biochemical reaction patterns, antimicrobial susceptibilities, and in vitro production of mucus. No correlation was found between the bacteria present in adenoidal tissue and middle ear effusions.