Cell-Penetration Peptide-Conjugated Octominin II Hybrid Inhibits the Multidrug-Resistant Shigella flexneri

Background/Objectives: The genus Shigella is one of the major pathological agents responsible for diarrhea and diarrhea-related mortality worldwide. It shows a decreasing sensitivity to most conventional antibiotics available today. Methods: Hence, an antimicrobial peptide, Octominin II, was conjugated to a cell-penetrating peptide (HIV-TAT) named TAT-Octominin II, and its antibacterial effect against Shigella flexneri was investigated. Results: TAT-Octominin II displayed minimum inhibitory and bactericidal concentrations of 10 and 25 µg/mL, respectively. It showed rapid membrane-permeabilizing activity, as observed in the ONPG assay. TAT-Octominin II treatment altered the cell membrane integrity and causing membrane damage in S. flexneri. Moreover, TAT-Octominin II increased oxidative stress, as evidenced by the upregulation of antioxidant genes, such as sodA, sodB, katG, oxyR, and soxR. Furthermore, TAT-Octominin II bound to genomic DNA and RNA, which likely inhibited the transcription and translation of bacterial proteins. In addition, TAT-Octominin II possessed lipopolysaccharide neutralization activity. In vitro toxicity analysis was performed using mammalian Raw 264.7 and HEK 293 cells, which showed no toxicity at lower concentrations (0–100 µg/mL). Conclusions: Overall, our results demonstrate that TAT-conjugated Octominin II exhibits enhanced antibacterial activity compared to Octominin II alone, suggesting that TAT-mediated delivery of AMPs could be a promising strategy to improve the therapeutic efficacy of AMPs.