Therapeutic potential of cationic steroid antibacterials

Polyketides as Secondary Metabolites from the Genus Aspergillus

Polyketides are an important class of structurally diverse natural products derived from a precursor molecule consisting of a chain of alternating ketone and methylene groups. These compounds have attracted the worldwide attention of pharmaceutical researchers since they are endowed with a wide array of biological properties. As one of the most common filamentous fungi in nature, Aspergillus spp. is well known as an excellent producer of polyketide compounds with therapeutic potential. By extensive literature search and data analysis, this review comprehensively summarizes Aspergillus-derived polyketides for the first time, regarding their occurrences, chemical structures and bioactivities as well as biosynthetic logics.

In situ potentiometric method to evaluate bacterial outer membrane-permeabilizing ability of drugs: example using antiprotozoal diamidines

We introduced a new assay system, combining tyrocidine A and a K(+)-selective electrode, to evaluate the bacterial outer membrane-permeabilizing ability of drugs. Tyrocidine A, in the presence of an outer membrane permeabilizer, increased the permeability to K(+) of the cytoplasmic membrane of Escherichia coli, because this antibiotic could markedly increase the permeability of phospholipid layers constituting the cytoplasmic membrane, while it acted weakly on the outer membrane. Hence, the novel function of agents increasing the permeability of the outer membrane could be examined directly by monitoring the tyrocidine A-induced leakage of K(+) from the bacterial cytoplasm using a K(+)-selective electrode. We found that antiprotozoal diamidines, such as diminazene, pentamidine, and 4',6-diamidino-2-phenylindole (DAPI), can increase the permeability of the bacterial outer membrane and appropriate lipophilicity is important for diamidines to permeabilize the outer membrane.

In vitro activity of aminosterols against yeasts involved in blood stream infections

Squalamine and other aminosterols have demonstrated interesting antimicrobial activities against clinical bacterial isolates and a limited number of reference yeast strains. We aimed to test whether squalamine and a synthetic aminosterol derivative (ASD) display any in vitro activity comparable to currently available systemic antifungals, an acceptable safety index, as well as to provide insights into their mechanism of action. The minimum inhibitory concentrations (MICs) of squalamine, ASD and available antifungals were determined against 21 yeast isolates that were recovered from cases of fungemia. Remarkably, homogeneous MICs ranging from 8-16 mg/L and from 1-2 mg/L were noted for squalamine and ASD, respectively, as opposes the heterogeneous in vitro activity of available systemic antifungals. Aminosterols induced haemolysis, a surrogate for toxic effects to mammalian cells, at concentrations high above their MICs. In time-kill studies, killing was as fast with ASD as with amphotericin B. Both aminosterols induced a time-dependent disruption of yeast membrane, as evidenced by gradual increase of ATP efflux. In conclusion, our preliminary data indicate that aminosterols have the potential to be further developed as antifungals. Additional work is warranted to assess their toxicity and activity in experimental models.