The widespread emergence of bacterial resistance to existing antibiotics forces the development of new therapeutic agents. The use of short modified oligonucleotides, such as peptide nucleic acids (PNAs), seems a promising strategy. However, the uptake of such oligonucleotides is limited by the bacterial cell wall and is species-dependent. Therefore, new carriers for PNAs should be extensively explored. In this study, we examined the antibacterial activity of vitamin B12–PNA conjugates. Vitamin B12 was covalently linked to a PNA oligomer targeted at the mRNA of an essential acpP gene encoding acyl carrier protein in Escherichia coli. PNA–vitamin B12 conjugates were synthesized using the Cu(I)-catalyzed 1,3-dipolar cycloaddition. We examined two types of linkers between vitamin B12 and PNA, including a cleavable disulfide bond. As a positive control for PNA uptake, we used PNA conjugated to the most widely used cell-penetrating peptide (KFF)3K. We found that vitamin B12–PNA conjugates inhibit E. coli growt...