Figure 5
Determination of opsonophagocytic activity with immunized sera against NTUH-K2044 and ATCC 13,883 by confocal micrograph. A RAW264.7 macrophage cells were infected with the serotype K1 NTUH-K2044 or the serotype K3 ATCC 13,883 containing the plasmid pLac-EGFP (green) at an MOI of 50 with or without 1:1100 final dilutions of sera from PBS-inoculated normal mice or 105 CFU ΔkbvR-immunized mice for 120 min, followed by treatment with 500 µg/mL gentamicin and staining with Alexa Fluor 594 dye (red) for actin cytoskeleton and DAPI (blue) for host cell nuclei. The opsonophagocytic activities of sera were observed under a confocal microscope. Arrows denote the intracellular bacteria. Scale bar = 5 μm. B The opsonophagocytic activities of sera against NTUH-K2044 were counted under a confocal microscope. Data are presented as the intracellular bacterial numbers in 300 cells from three independent trials. C The opsonophagocytic activities of sera against ATCC 13,883 were determined by the phagocytic rate. The mean opsonophagocytic ratio was calculated by the formula = 100 ⋅ CFU of intracellular phagocytized bacteria/CFU of input bacteria. *: P < 0.05; **: P < 0.01; ****: P < 0.0001.