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Aims: Emergence and rapid dissemination of antibiotic-resistant bacteria is becoming a severe problem to public health. The search for antimicrobial substitutes for antibiotics is necessary. Lactoferricin B like peptide (LBLP) is a 23-mer antimicrobial peptide (AMP), derived from the big centipede Scolopendra subspinipes mutilans. Although its antifungal effect and its mechanism have been reported, the antibacterial activity has not yet been elucidated., Method and Results: In this study, we investigated antibacterial activity of LBLP and its mode of action. LBLP showed potent antibacterial effect against pathogenic bacteria Escherichia coli and did not show haemolytic activity against human erythrocyte. The general antimicrobial mechanism of AMP is to disrupt the cell membrane, however, LBLP exerted its antibacterial activity by causing apoptosis-like death through reactive oxygen species (ROS) generation. LBLP-treated E. coli cells exhibited hallmarks of apoptosis, such as membrane depolarization, DNA fragmentation, caspase-like protein activation and phosphatidylserine exposure. These apoptotic features were attenuated by pretreatment of NAC, a representative ROS scavenger., Conclusions: These results demonstrate that LBLP exerted its antibacterial activity by generating ROS and inducing apoptosis-like death in E. coli. LBLP is not membrane destructive per se, but essentially a metabolic inhibitor., Significance and Impact of the Study: Lactoferricin B like peptide is potential candidate to replace conventional antibiotics that are less effective because of its unique properties., (© 2020 The Society for Applied Microbiology.)

Aims: Metal nanoparticles are promising materials for the management of infectious diseases as known to have various antimicrobial activities in pathogenic micro-organisms. Among them, gold nanoparticles (AuNPs) are used in a wide range of fields such as photodynamic therapy, molecular diagnostics and drug delivery because of their unique physicochemical properties. However, little is known about the synergistic antibacterial activity and mechanism of AuNPs on pathogenic bacteria., Methods and Results: Combinations of AuNPs and cefotaxime and ciprofloxacin showed synergistic interaction against all Salmonella species, however the combination with kanamycin exhibited no interaction. We determined that AuNPs and in combinations with antibiotics exert its antibacterial effect through bacterial apoptosis-like death. AuNPs caused collapse of intracellular divalent cation homeostasis, and conventional antibiotics caused accumulation of reactive oxygen species, which induced apoptotic hallmarks such as membrane depolarization, caspase-like protein activation, cell filamentation and phosphatidylserine externalization., Conclusions: The cation homeostasis disruption by AuNPs and the accumulation of reactive oxygen species by conventional antibiotics synergistically affected bacterial cell death and induced apoptosis-like death in Salmonella cells., Significance and Impact of the Study: The synergistic activity between AuNPs and antibiotics propose that the AuNPs are a potential antibacterial agent and adjuvant for antimicrobial chemotherapy., (© 2019 The Society for Applied Microbiology.)