Antibacterial activity and mechanism of X33 antimicrobial oligopeptide against Acinetobacter baumannii.

Acinetobacter baumannii is a pathogenic bacterium widespread in human environments, especially in intensive care units, and is associated with high morbidity and infection rates. Multiple drug resistance in A. baumannii frequently leads to the death of patients, making the development of multi-effect antibacterial agents against this bacterium a research hotspot. We have previously found that the X33 antimicrobial oligopeptide can effectively inhibit the growth of Penicillium digitatum and Candida albicans. Herein, we evaluated the antibacterial activity of X33 antimicrobial oligopeptide against A. baumannii by determining the minimum inhibitory concentration, inhibition zone, and growth curve. The increase in extracellular alkaline phosphatase and the leakage of intracellular compounds confirmed the effect of X33 antimicrobial oligopeptide on the cell wall and membrane. Changes in reactive oxygen species, malondialdehyde, ATP, reducing sugar, soluble protein, and pyruvate content demonstrated that the incubation with X33 antimicrobial oligopeptide affected energy metabolism and oxidative stress. Consistent with the physiological characteristics, transcriptomics analysis indicated that incubation with X33 antimicrobial oligopeptide significantly induced changes in the expression of 2339 genes, including 1262 upregulated and 1077 downregulated genes, which participate in oxidative phosphorylation, ribosome, quorum sensing, fatty acid degradation, glycolysis/gluconeogenesis, and citrate cycle pathways. These results provide a fundamental basis for investigating the mechanism of X33 antimicrobial oligopeptide as a potential drug against A. baumannii.

Physiological and transcriptome analysis of Candida albicans in response to X33 antimicrobial oligopeptide treatment.

Introduction: Candida albicans is an opportunistic pathogenic fungus, which frequently causes systemic or local fungal infections in humans. The evolution of its drug-resistant mutants necessitate an urgent development of novel antimicrobial agents. Results: Here, we explored the antimicrobial activity and inhibitory mechanisms of X33 antimicrobial oligopeptide (X33 AMOP) against C. albicans. The oxford cup test results showed that X33 AMOP had strong inhibitory activity against C. albicans, and its MIC and MFC were 0.625 g/L and 2.5 g/L, respectively. Moreover, SEM and TEM showed that X33 AMOP disrupted the integrity of cell membrane. The AKP, ROS, H2O2 and MDA contents increased, while the reducing sugar, soluble protein, and pyruvate contents decreased after the X33 AMOP treatment. This indicated that X33 AMOP could damage the mitochondrial integrity of the cells, thereby disrupting the energy metabolism by inducing oxidative stress in C. albicans. Furthermore, transcriptome analysis showed that X33 AMOP treatment resulted in the differential expression of 1140 genes, among which 532 were up-regulated, and 608 were down-regulated. These DEGs were related to protein, nucleic acid, and carbohydrate metabolism, and their expression changes were consistent with the changes in physiological characteristics. Moreover, we found that X33 AMOP could effectively inhibit the virulence attributes of C. albicans by reducing phospholipase activity and disrupting hypha formation. Discussion: These findings provide the first-ever detailed reference for the inhibitory mechanisms of X33 AMOP against C. albicans and suggest that X33 AMOP is a potential drug candidate for treating C. albicans infections.

Combined transcriptome and metabolome analyses reveal the potential mechanism for the inhibition of Penicillium digitatum by X33 antimicrobial oligopeptide.

Penicillium digitatum is the primary spoilage fungus that causes green mold during postharvest in citrus. To reduce economic losses, developing more efficient and less toxic natural antimicrobial agents is urgently required. We previously found that the X33 antimicrobial oligopeptide (X33 AMOP), produced by Streptomyces lavendulae X33, exhibited a sterilization effect on P. digitatum. In this study, the effects, and physiological mechanisms of X33 AMOP as an inhibitor of P. digitatum were investigated. The transcriptional and metabolome profiling of P. digitatum exposed to X33 AMOP revealed 3648 genes and 190 metabolites that were prominently changed. The omics analyses suggested that X33 AMOP mainly inhibited P. digitatum growth by affecting cell integrity, genetic information delivery, oxidative stress tolerance, and energy metabolism. These findings provide helpful information regarding the antimicrobial mechanism of X33 AMOP against P. digitatum at the molecular level and indicate that X33 AMOP is a potential candidate to control P. digitatum.