Most Streptococcus pneumoniae strains are killed by very low concentrations of penicillin and other 13-lactam antibiotics, yet middle ear inflammation and effusion persist for days to weeks after treatment in most cases of pneumococcal otitis media. To study the effect of 13-lactam antibiotic treatment on pneumococci and the middle ear inflammatory response during pneumococcal otitis media, we measured concentrations of pneumococci, inflammatory cells, and lysozyme in middle ear fluid (MEF) by using the chinchilla model. Procaine penicillin

To determine whether oxidative metabolic products of phagocytic cells are present in the middle ear during experimental pneumococcal otitis media, we measured the concentration of myeloperoxidase (MPO) in middle ear fluid (MEF) and the capacity of neutrophils isolated from MEF and peripheral blood to produce MPO and superoxide anion (O2-) after in vitro stimulation. Free MPO in MEF was significantly increased 24 and 48 h after either viable or nonviable pneumococci were inoculated into the middle ear. In vitro-stimulated production of MPO and O2- from middle ear neutrophils was significantly less than that from peripheral blood neutrophils 24 h after nonviable pneumococci were inoculated but similar to it after 48 h. Twenty-four hours after viable pneumococci were inoculated, middle ear neutrophils stimulated in vitro produced less MPO but the same amount of O2- as did blood neutrophils. Oxidative metabolic products, therefore, are released from phagocytic cells into the MEF during pneumococcal otitis media, and future studies will need to define the contribution of these products to acute and chronic middle ear tissue injury.

The pathogenesis of middle ear inflammation caused by Streptococcus pneumoniae was explored in the chinchilla model with different pneumococcal cell wall (CW) preparations, including isolated native CW, M1 muramidase CW (M1-CW) digest, amidase CW digest, and M1 peptidoglycan (M1-PG) digest. Inflammatory cell and lysozyme concentrations in middle ear fluid (MEF) were measured between 6 and 72 h after the middle ears were inoculated with one of the preparations or sterile saline. Middle ear histopathology was measured quantitatively at 72 h. Native CW, M1-CW digest, and amidase-CW digest caused significantly more inflammatory cell influx and lysozyme accumulation in MEF than saline did. M1-PG digest also caused more inflammatory cell influx and lysozyme accumulation in MEF than saline did but caused less inflammation than native CW or either CW digest. Epithelial metaplasia was significantly greater in ears inoculated with native CW than in ears inoculated with the CW or PG digest or with saline. Pneumococcal CW is, therefore, the principal factor that initiates middle ear inflammation in acute pneumococcal otitis media, and CW teichoication seems to be important in initiating this response.

Middle ear inflammation in acute bacterial otitis media is characterized by accumulation of neutrophils in middle ear effusion. Since neutrophils release products that may injure surrounding tissues, we studied the effect of neutrophil metabolic products on middle ear epithelial cells (MEECs) in vitro. Chinchilla MEECs were incubated with phorbol myristate acetate (PMA)-activated human neutrophils or with hydrogen peroxide (H2O2). Cell growth, which was measured by 3H-thymidine incorporation, was inhibited by activated neutrophils and by H2O2. Unstimulated neutrophils, PMA alone, and catalase alone did not affect the viability of MEECs. Catalase, an enzyme that reduces H2O2, partially blocked the inhibitory effect of activated neutrophils and completely blocked the inhibitory effect of H2O2. Inhibition of MEEC metabolism by neutrophil-reactive oxygen species may contribute to epithelial injury, which may prolong the middle ear inflammatory response and lead to chronic tissue damage.

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