Inhibiting the growth of methicillin-resistant Staphylococcus aureus in vitro with antisense peptide nucleic acid conjugates targeting the ftsZ gene

Background: The increasing emergence of clinical infections caused by methicillin-resistant Staphylococcus aureus (MRSA) challenges existing therapeutic options and highlights the need to develop novel treatment strategies. The ftsZ gene is essential to bacterial cell division. Methods: In this study, two antisense peptide nucleic acids (PNAs) conjugated to a cell-penetrating peptide were used to inhibit the growth of MRSA. PPNA1, identified with computational prediction and dot-blot hybridization, is complementary to nucleotides 309-323 of the ftsZ mRNA. PPNA2 was designed to target the region that includes the translation initiation site and the ribosomal-binding site (Shine-Dalgarno sequence) of the ftsZ gene. Scrambled PPNA was constructed with mismatches to three bases within the antisense PPNA1 sequence. Results: PPNA1 and PPNA2 caused concentration-dependent growth inhibition and had bactericidal effects. The minimal bactericidal concentrations of antisense PPNA1 and PPNA2 were 30 mu mol/l and 40 mu mol/l, respectively. The scrambled PPNA had no effect on bacterial growth, even at higher concentrations, confirming the sequence specificity of the probes. RT-PCR showed that the antisense PPNAs suppressed ftsZ mRNA expression in a dose-dependent manner. Conclusion: Our results demonstrate that the potent effects of PNAs on bacterial growth and cell viability were mediated by the down-regulation or even knock-out of ftsZ gene expression. This highlights the utility of ftsZ as a promising target for the development of new antisense antibacterial agents to treat MRSA infections. (C) 2014 The Authors. Published by Elsevier Ltd on behalf of International Society for Infectious Diseases. This is an open access article under the CC BY-NC-ND license