Figure 3. Erythrocytes inhibit pneumococcal growth by reactive oxygen species-related mechanism.

S. pneumoniae cells (∼1×10² CFU, 10 µl) were added to erythrocytes (5×10⁹ cells/ml, 190 µl) with or without 1 mM 2,2′-bipyridyl (iron chelator), 1 mM S-ethyl-ITU (nitric oxide synthase inhibitor), 100 µM EUK8 (synthetic catalytic free radical scavenger), or 150 µM MnTBAP (superoxide dismutase mimetic) for 2 hours at 37°C in a 5% CO₂ atmosphere. Next, each mixture was serially diluted and plated on TS blood agar. Following incubation, CFU values were determined. *Significant difference (P<0.005) between mean values, as determined with a Mann-Whitney U-test. The experiments were performed 3 times and data are shown as the mean of 6 wells from a representative experiment. S.D. values are represented by vertical lines.