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β-Galactosidase activity of lacZ transcriptional fusions of three invasion genes (white bars, hilA; gray bars, invF; black bars, orgA) in S. Typhimurium subpopulations. The LD, MD, and HD cell subpopulations were obtained using Radioselectan density gradient ultracentrifugation after 10, 24, and 48 h of culture. The standard deviations for the triplicate β-galactosidase assays are so small that error bars are not visible. Results are representative of three independent experiments.
