Inhibition of Intracellular Growth of Salmonella enterica serovar typhimurium in Tissue Culture by Antisense Peptide-Phosphorodiamidate Morpholino Oligomer

Two types of phosphorodiamidate morpholino oligomers (PMOs) were tested for inhibition of growth of Salmonella enterica serovar typhimurium. Both PMOs have the same 11-base sequence that is antisense to the region near the start codon of acpP, which is essential for lipid biosynthesis and viability. To the 3'end of each is attached the membrane-penetrating peptide (RXR)4XB (R, X, and B indicate arginine, 6-aminohexanoic acid, and beta-alanine, respectively). One PMO (AcpP PPMO) has no charge on the PMO moiety. The second PMO has 3 cations (piperazine) attached to the phosphorodiamidate linkages (3+Pip-AcpP PPMO). A scrambled-sequence (Scr) PMO-(RXR)4XB conjugate was synthesized for each type of PMO. The MIC of AcpP PPMO, 3+Pip-AcpP PPMO, and either Scr PPMO was 1.25 microM (7 microg/ml), 0.156 microM (0.94 microg/ml), and >160 microM (> 900 microg/ml), respectively. 3+Pip-AcpP PPMO at 1.25 or 2.5 microM significantly reduced the growth rates of pure cultures, whereas AcpP PPMO or either Scr PPMO had no effect. However, the viable cell count was significantly reduced at either concentration of 3+Pip-AcpP PPMO or AcpP PPMO, but not with either Scr PPMO. In other experiments, macrophages were infected intracellularly with S. enterica and treated with 3 microM 3+Pip-AcpP PPMO. Intracellular bacteria were reduced >99% with 3+Pip-AcpP PPMO, whereas intracellular bacteria increased 3 orders of magnitude in untreated or Scr PPMO-treated cultures. We conclude that either AcpP PPMO or 3+Pip-AcpP PPMO inhibited growth of S. enterica in pure culture, and that 3+Pip-AcpP PPMO reduced intracellular viability of S. enterica in macrophages.