Antibacterial activities of novel peptide nucleic acids targeting Salmonella penicillin-binding proteins

<i>Salmonella</i> is a significant global enteric pathogen with a high incidence of multidrug resistance (MDR), which limits therapeutic options and necessitates the development of novel treatments. Antisense peptide nucleic acids (PNAs), which target essential bacterial genes, have demonstrated potential as antibacterial agents by effectively inhibiting the growth of various pathogens. Peptidoglycan (PG) has historically been one of the central targets for antibiotics in the ongoing battle against pathogenic bacteria. In this study, PNAs conjugated to the cell-penetrating peptide (CPP) (KFF)3K were designed to target three essential genes based on the genome sequence of the MDR <i>Salmonella</i> Typhimurium strain SL1344: ftsI (encoding penicillin-binding protein [PBP] 3), mrcB (PBP1B), and mrdA (PBP2). These CPP-PNA conjugates showed dose-dependent antibacterial activity <i>in vitro</i> and <i>in vivo</i>, with the anti-<i>mrdA</i> CPP-PNA demonstrating the strongest inhibition. The results were associated with selective expression inhibition of the targeted genes. Morphological analysis confirmed that the antisense inhibition of <i>Salmonella</i>-targeted genes led to interference with the cell division and elongation. Consistently, treatment with these CPP-PNAs significantly improved the survival of <i>Caenorhabditis elegans</i> in an intestinal infection model. These findings present a viable approach for addressing MDR <i>Salmonella</i> infections using the antisense-based therapy.