Control of human and plant fungal pathogens using pentaene macrolide 32, 33-didehydroroflamycoin.

AIMS: The aim of this study was to address the toxicity of recently described polyene macrolide 32, 33-didehydroroflamycoin (DDHR) on a wide range of fungal pathogens and its potential to control plant fungal diseases. METHODS AND RESULTS: The antifungal activity of DDHR in vitro was examined against common human and plant pathogenic fungi using a broth microdilution assay and a disk diffusion assay. Minimum inhibitory concentrations ranged from 12·5 to 35 µg ml(-1) . A radial growth inhibition assay showed that DDHR inhibited mycelia growth, inducing mycelial necrosis and affecting sporulation. During the in vivo assay on apple fruits administration of DDHR 1 h before fungal inoculation inhibited spreading of the infection. Importantly, DDHR exhibited no phytotoxic effects on the model plant, Capsicum annum, verified by the plant growth rate and chlorophyll content. CONCLUSIONS: DDHR inhibits growth of various plant pathogens in vitro with the strongest activity against Alternaria alternata, Colletotrichum acutatum and Penicillium expansum, and protects apple fruits from decay. SIGNIFICANCE AND IMPACT OF THE STUDY: This is the first report of the inhibitory effect of DDHR on important pathogenic fungal isolates. DDHR could be a good scaffold for developing new antifungal agents for fruit and vegetable protection.

Didehydroroflamycoin pentaene macrolide family from Streptomyces durmitorensis MS405(T) : production optimization and antimicrobial activity.

AIMS: The aim of this study was to improve production of pentaene 32,33-didehydroroflamycoin (DDHR) in Streptomyces durmitorensis MS405 strain to obtain quantities sufficient for in depth analysis of antimicrobial properties. METHODS AND RESULTS: Through classical medium optimization conditions for stable growth, DDHR production within 7 days of incubation was established. Yields of 215 mg l(-1) were achieved in shake flask experiments in complex medium with mannitol as the primary carbon source. DDHR had poor antibacterial activity with minimal inhibitory concentrations (MIC) of 400 µg ml(-1) for Staphylococcus aureus and Bacillus subtilis, while MIC of 70 µg ml(-1) was determined for Candida albicans. Using flow cytometry and fluorescent microscopy, it was demonstrated that DDHR induced membrane damage in C. albicans followed by cell death. Combination studies with known antifungal nystatin showed that DDHR is a promising agent for the development of novel antimycotic treatments potentially less toxic for human cells. CONCLUSIONS: Pentaene didehydroroflamycoin has no antibacterial activity but can be further developed for the application in antifungal therapy. SIGNIFICANCE AND IMPACT OF THE STUDY: This study is the first report on the stable and production in high yields of a novel pentaene family that acts on Candida cell membranes and can be used in combination with known antifungals. Polyenes are still antifungal antibiotics of choice, and therefore, isolation and production of new lead structures are highly significant.

Spontaneous formation of IpaB ion channels in host cell membranes reveals how Shigella induces pyroptosis in macrophages.

The Gram-negative bacterium Shigella flexneri invades the colonic epithelium and causes bacillary dysentery. S. flexneri requires the virulence factor invasion plasmid antigen B (IpaB) to invade host cells, escape from the phagosome and induce macrophage cell death. The mechanism by which IpaB functions remains unclear. Here, we show that purified IpaB spontaneously oligomerizes and inserts into the plasma membrane of target cells forming cation selective ion channels. After internalization, IpaB channels permit potassium influx within endolysosomal compartments inducing vacuolar destabilization. Endolysosomal leakage is followed by an ICE protease-activating factor-dependent activation of Caspase-1 in macrophages and cell death. Our results provide a mechanism for how the effector protein IpaB with its ion channel activity causes phagosomal destabilization and induces macrophage death. These data may explain how S. flexneri uses secreted IpaB to escape phagosome and kill the host cells during infection and, may be extended to homologs from other medically important enteropathogenic bacteria.