Intracellular growth of multicopy inducible PC-PLC L. monocytogenes strains in Henle 407 cells. Overnight cultures of L. monocytogenes strains were diluted 1:10 in BHI medium and grown for 2 h at 37°C in the presence or absence of 10 mM IPTG. Monolayers of Henle 407 cells were infected at an MOI of 50:1, and intracellular growth was measured in the presence or absence of 10 mM IPTG as described in Materials and Methods. (A) SLCC-5764 (PrfA*) strain derivatives. Symbols: •, DH-L683 (SLCC-5764 Δhly, pAMspacOid); ○, DH-L687 (SLCC-5764 Δhly ΔplcB, pAMspacOid); ▵, DH-L735 (SLCC-5764 Δhly ΔplcB, pAMiplcB) without IPTG; ▴, DH-L735 (SLCC-5764 Δhly ΔplcB, pAMiplcB) with 10 mM IPTG. (B) 10403S (PrfA) strain derivatives. Symbols: •, DH-L728 (10403S Δhly, pAMspacOid); ○, DH-L729 (10403S Δhly ΔplcB, pAMspacOid); ▵, DH-L824 (10403S Δhly ΔplcB, pAMiplcB) without IPTG; ▴, DH-L824 (10403S Δhly ΔplcB, pAMiplcB) with 10 mM IPTG. The data points in the growth curves in panels A and B represent the means ± standard deviations of three coverslips from one of three experiments and from one experiment, respectively.