OBJECTIVES: Antimicrobial resistance is an increasingly life-threatening problem that emphasizes the need to develop new antibacterial agents. The in vitro antibacterial activity of squalamine, a natural aminosterol, has been previously demonstrated against multidrug-resistant bacteria and moulds. Although the antibacterial activity of squalamine was found to correlate with that of other drugs, such as colistin, against Gram-negative bacteria, the former was active against Gram-positive bacteria, which are resistant to colistin. In this work, we provide new insights into squalamine's antibacterial mechanism of action compared with other known antibiotics. METHODS: We evaluated squalamine's antibacterial mechanism of action using the broth microdilution method for MIC determination and time-kill assays, transmission electron microscopy for morphological change studies, bioluminescence for ATP release measurements and fluorescence methods for membrane depolarization assays. RESULTS: Concerning Gram-negative bacteria, squalamine, similar to colistin, required interaction with the negatively charged phosphate groups in the bacterial outer membrane as the first step in a sequence of different events ultimately leading to the disruption of the membrane. Conversely, squalamine exhibited a depolarizing effect on Gram-positive bacteria, which resulted in rapid cell death. CONCLUSIONS: The new insights into the mechanism of action of squalamine highlight the importance of aminosterols in the design of a new class of antibacterial compounds that could be used as disinfectants and detergents.
OBJECTIVES: Antimicrobial resistance is an increasingly life-threatening problem that emphasizes the need to develop new antibacterial agents. The in vitro antibacterial activity of squalamine, a natural aminosterol, has been previously demonstrated against multidrug-resistant bacteria and moulds. Although the antibacterial activity of squalamine was found to correlate with that of other drugs, such as colistin, against Gram-negative bacteria, the former was active against Gram-positive bacteria, which are resistant to colistin. In this work, we provide new insights into squalamine's antibacterial mechanism of action compared with other known antibiotics. METHODS: We evaluated squalamine's antibacterial mechanism of action using the broth microdilution method for MIC determination and time-kill assays, transmission electron microscopy for morphological change studies, bioluminescence for ATP release measurements and fluorescence methods for membrane depolarization assays. RESULTS: Concerning Gram-negative bacteria, squalamine, similar to colistin, required interaction with the negatively charged phosphate groups in the bacterial outer membrane as the first step in a sequence of different events ultimately leading to the disruption of the membrane. Conversely, squalamine exhibited a depolarizing effect on Gram-positive bacteria, which resulted in rapid cell death. CONCLUSIONS: The new insights into the mechanism of action of squalamine highlight the importance of aminosterols in the design of a new class of antibacterial compounds that could be used as disinfectants and detergents.