Combined antimicrobial effect of two peptide nucleic acids against Staphylococcus aureus and S. pseudintermedius veterinary isolates

and are the major etiological agents of staphylococcal infections in humans, livestock, and companion animals. The misuse of antimicrobial drugs has led to the emergence of antimicrobial-resistant spp., including methicillin-resistant (MRSA) and methicillin-resistant (MRSP). One novel therapeutic approach against MRSA and MRSP is a peptide nucleic acid (PNA) that can bind to the target nucleotide strands and block expression. Previously, two PNAs conjugated with cell-penetrating peptides (P-PNAs), antisense PNA (ASP)-cmk and ASP-deoD, targeting two essential genes in , were constructed, and their antibacterial activities were analyzed. This study analyzed the combined antibacterial effects of P-PNAs on and clinical isolates. ATCC 29740 cells were treated simultaneously with serially diluted ASP-cmk and ASP-deoD, and the minimal inhibitory concentrations (MICs) were measured. The combined P-PNA mixture was then treated with and veterinary isolates at the determined MIC, and the antibacterial effect was examined. The combined treatment of two P-PNAs showed higher antibacterial activity than the individual treatments. The MICs of two individual P-PNAs were 20 and 25 μM, whereas that of the combined treatment was 10 μM. The application of a combined treatment to clinical spp. revealed isolates to be resistant to P-PNAs and isolates to be susceptible. These observations highlight the complexity of designing ASPs with high efficacy for potential applications in treating staphylococcal infections in humans and animals.