Abstract:
Two different types of Phosphorodiamidate Morpholino Oligomers (PMOs) were used to
inhibit growth in pure cultures of Salmonella enterica serovar typhimurium and in mouse
macrophages infected with S. typhimurium. Both PMOs were 11 bases long and
complementary to bases 6-16 of acyl carrier protein mRNA. A membrane-penetrating
peptide, (RXR)4XB, was attached to the 3’ end of both PMOs (R is arginine, X is 6-
aminohexanoic acid, and B is β-alanine). One PMO (AcpP) had the standard neutral
linkages while the other (Pip-AcpP) was modified with three cationic piperazines
interspersed between the linkages. Scrambled sequence controls of both types of PMOs
were synthesized (Scr, Pip-Scr). The minimal inhibitory concentrations (MIC) of the
AcpP, Pip-AcpP, Scr, and Pip-Scr were 1.25 μM, 0.156 μM, >160 μM, and >160 μM
respectively. The growth curve assay showed that Pip-AcpP significantly inhibited
growth at 2.5 μM as compared to an untreated control. There was no inhibition for AcpP,
Scr, or Pip-Scr at the same concentration. The tissue culture assay showed that Pip-AcpP
reduced the viability of S. typhimurium growing intracellularly in mouse macrophages by
5 to 6 orders of magnitude over 48 hours. The Pip-Scr showed no inhibition over the
same period. In conclusion, the Pip-AcpP proved to more effective than AcpP in pure
culture and was able to significantly reduce bacterial growth in tissue culture as well.
