Free radical production by antibiotic-killed bacteria in the guinea pig middle ear

Objectives: Oxygen free radicals are implicated in the pathogenesis of otit is media. Recent investigations with animal models have demonstrated that f ree radical-mediated damage of the middle ear mucose, measured as lipid hyd roperoxide, occurs when the middle ear cavity is inoculated with Streptococ cus pneumoniae, The present study was conducted to examine the effect of an tibiotics on free radical-mediated damage in pneumococcal acute otitis medi a. Study Design: Animal model of acute otitis media. Methods: Seventy-eight guinea pigs underwent bilateral middle ear inoculation with 100 mul of 1) sterile saline as a control, 2) 50 mug/mL amoxicillin, 3) 10(7) colony form ing units (CFU)/mL Streptococcus pneumoniae killed with 50 mug/mL amoxicill in, or 4) 10(7) CFU/mL S pneumoniae, Animals were killed on postoperative d ay 1 or 5, and the middle ear mucosa was examined for lipid peroxidation as evidence of free radical damage. Results: Mucosal lipid hydroperoxide was significantly elevated compared with control subjects on day 1 in both the antibiotic-killed S pneumoniae group and the S pneumoniae-infected group. O n day 5, the S pneumoniae-infected mucosa had significantly higher lipid hy droperoxide levels compared with the antibiotic-killed group and the contro l subjects, Histological studies confirmed mucosal edema and the presence o f inflammatory cells in the infected groups. Conclusions: Antibiotic-killed bacteria seem to produce free radical-mediated damage to the middle ear mu cosa in the early phase of acute otitis media The clinical implication of t his study is that free radical damage to the middle ear mucosa may occur in otitis media despite appropriate antibiotic therapy.