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Serum inhibition assay. Persistent- and transient-infection strains and the P1 Δwca mutant were grown in 50% LB broth and either 50% fresh normal bovine serum (A) or heat-inactivated serum (B), as indicated. Optical density (at 600 nm) was monitored in five replicate wells for each bacterial strain, and the experiment was repeated three times. Groups of strains that were statistically different (P < 0.05) are indicated by different lowercase letters.
