Squalamine: an appropriate strategy against the emergence of multidrug resistant gram-negative bacteria?

Abstract

We reported that squalamine is a membrane-active molecule that targets the membrane integrity as demonstrated by the ATP release and dye entry. In this context, its activity may depend on the membrane lipid composition. This molecule shows a preserved activity against bacterial pathogens presenting a noticeable multi-resistance phenotype against antibiotics such as polymyxin B. In this context and because of its structure, action and its relative insensitivity to efflux resistance mechanisms, we have demonstrated that squalamine appears as an alternate way to combat MDR pathogens and by pass the gap regarding the failure of new active antibacterial molecules.

Figure 1. Gram negative bacteria envelope.

Figure 2. Structure of squalamine 1.

Figure 3. Measurement of squalamine concentration effect on E. coli ATP efflux.

Figure 4. Effect of squalamine on bacterial membrane integrity assessed by fluorescence measurement of propidium iodide – DNA/RNA interactions.

Results are expressed in relative fluorescence unit (RFU) as Mean±S.D. (n = 3, three independent experiments).

Figure 5. Fluorescence-based microscopic evaluation of the effect of squalamine on bacterial integrity and survival.

E. Coli cultures (10⁹/mL) were either left untreated (A) or treated with increasing squalamine concentrations: 1.25 µg/mL (B), 2.5 µg/mL (C), 5 µg/mL (D), 10 µg/mL (E), 100 µg/ml (F). Suspensions of cultured E. Coli were then stained with the Live/Dead BacLight bacterial Viability kit, as described in material and methods. Scale bar (10 µm).

Figure 6. ATP efflux inhibition in E. coli in the presence of squalamine (5 µg/mL) and various mono and divalent salt solutions.