Figure 5. Intracellular survival/replication.

Int-407 cells were infected with exponential M9 or LB cultures of the indicated strains of S. Typhimurium for 15 min at 37°. At this time point non-adherent bacteria were removed and extracellular bacteria were killed by gentamicin. To determine intracellular survival/replication intracellular bacteria were enumerated by plating after 2 hrs and 8 hrs, respectively. The strains tested are: wt; S. Typhimurium 4/74, spe (biosynthesis), pot (transport), spe/pACYC177; spe-mutant with blank complementation plasmid, spe/pLOJ318; spe-mutant complemented with speB (putrescine biosynthesis). pot/pLOJ326; pot-mutant complemented with potCD (spermidine/putrescine uptake). +p and +s denotes that the bacterial cultures have been supplemented with 100 µg ml⁻¹ of putrescine or spermidine, respectively, prior to invasion. The experiments were repeated at least 4 times with similar results and shown is an average of these. Errorbars indicate standard deviation. Significant differences between wt grown in M9 vs other strains/growth conditions are indicated as follows: ** = P<0.001; * = P<0.05. The P-values were calculated by a one-way ANOVA using Dunnets post-test.