FIG. 5.
F1 antibodies block Y. pestis type III injection, which is overcome by caf1A::IS1541. (A) Human anticoagulated blood was incubated for 120 or 240 min with 105 CFU Y. pestis KIM D27 or the isogenic ΔF1 mutant strain in the absence (−) or presence of mouse anti-F1 (αF1) or a nonreactive serum control (NR). Mean changes in bacterial load were recorded by plating aliquots on agar and incubating the preparations for colony formation (CFU). (B to E) HeLa tissue culture cells were viewed by differential interference contrast (DIC) microscopy, or their actin cables were stained with rhodamine-phalloidin and viewed by fluorescence microscopy. Tissue culture cells were either not infected (B) or were infected with plague strains in the presence or absence of 500 μg F1-specific MAb F1-04-A-G1 (MAb F1) using Y. pestis KIM D27 (C), ΔF1 (caf1 deletion) (D), and CAC2 (caf1A::IS1541) (E).