Free Radical Production by Antibiotic-Killed Bacteria in the Guinea Pig Middle Ear

Objectives Oxygen free radicals are implicated in the pathogenesis of otitis media. Recent investigations with animal models have demonstrated that free radical–mediated damage of the middle ear mucosa, measured as lipid hydroperoxide, occurs when the middle ear cavity is inoculated with Streptococcus pneumoniae. The present study was conducted to examine the effect of antibiotics on free radical–mediated damage in pneumococcal acute otitis media. Study Design Animal model of acute otitis media. Methods Seventy‐eight guinea pigs underwent bilateral middle ear inoculation with 100 μl of 1) sterile saline as a control, 2) 50 μg/mL amoxicillin, 3) 107 colony forming units (CFU)/mL Streptococcus pneumoniae killed with 50 μg/mL amoxicillin, or 4) 107 CFU/mL S pneumoniae. Animals were killed on postoperative day 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. On day 5, the S pneumoniae–infected mucosa had significantly higher lipid hydroperoxide levels compared with the antibiotic‐killed group and the control subjects. Histological studies confirmed mucosal edema and the presence of inflammatory cells in the infected groups. Conclusions Antibiotic‐killed bacteria seem to produce free radical–mediated damage to the middle ear mucosa in the early phase of acute otitis media. The clinical implication of this study is that free radical damage to the middle ear mucosa may occur in otitis media despite appropriate antibiotic therapy.