FIG. 1.

Effect of ciprofloxacin on the killing of A. actinomycetemcomitans. A. actinomycetemcomitans was added to tubes containing 20% human serum (Aa only), control PMNs in 20% serum (Aa with control PMNs), 0.5 μg of ciprofloxacin/ml in 20% serum (Aa with ciprofloxacin), or ciprofloxacin-loaded PMNs in 20% serum containing 0.5 μg of ciprofloxacin/ml (Aa, PMNs & ciprofloxacin). The suspensions were rotated at 37°C for 2 h, and aliquots were removed every 30 min and diluted for assessment of bacterial killing. Data are presented as the means ± standard errors of the means (SEM) of three separate experiments performed with PMNs obtained from different donors. The experiments represented in the upper panel utilized bacteria-to-PMN ratios of 10:1. PMNs loaded with ciprofloxacin killed significantly more bacteria than ciprofloxacin alone at 30, 60, 90, and 120 min (P < 0.05; Tukey's test), but failed to kill significantly more bacteria than control PMNs (P > 0.05). The experiments whose results are presented in the lower panel were conducted with 30 bacteria per PMN. Under these conditions, PMNs loaded with ciprofloxacin killed significantly more bacteria than control PMNs at every time point between 30 and 120 min. Moreover, ciprofloxacin-loaded PMNs killed more bacteria than ciprofloxacin alone at 30 and 60 min (P < 0.05; Tukey's test).