In Vitro and In Vivo Activity of a Novel Antisense Peptide Nucleic Acid Compound Against Multidrug-Resistant Acinetobacter baumannii

Multidrug-resistant (MDR) Acinetobacter baumannii is a difficult pathogen due to its propensity to develop resistance to antibiotics. Antisense nucleic acid analogs have been proposed as a potential alternative anti-infective approach. We developed a peptide nucleic acid (PNA) compound that targets the essential Acinetobacter gene carA. The PNA oligomer was conjugated to the cell-penetrating peptide (RXR)(4)XB. In vitro testing of the PNA conjugate against four clinical strains of MDR-A. baumannii in minimal medium demonstrated that all four strains were inhibited at a concentration of 1.25 mu M. In vivo testing of the PNA conjugate was done using a Galleria mellonella model of sepsis caused by one of the clinical strains. Preliminary testing of a variety of inocula demonstrated that an inoculum of 1 x 10(6) cfu was lethal to the majority of caterpillars by day 3, but not within 24 hours. The PNA compound was administered 30 minutes after an inoculum of 1 x 10(6) cfu at doses estimated to produce concentrations of similar to 5 and 20 mu M. The PNA compound had no effect at the lower dose. However, the higher dose reduced mortality from 5/28 (18%) to 0/28 (0%) at day 1 (p = 0.051) and from 19/28 (68%) to 9/28 (32%) at day 6 (p = 0.015). Antisense therapy is a novel approach to dealing with difficult MDR pathogens that could circumvent the problem of progressive resistance to available antibiotics. Further studies need to be done with additional strains and more complex in vivo model systems.