Plectasin - a new weapon against highly resistant microbes ?..

We know that Plectasin, found in Pseudoplectania nigrella (see picture), is the first defensin to  be isolated from a fungus. Plectasin has a chemical structure resembling defensins found in spiders, scorpions, dragonflies and mussels. In laboratory tests, Plectasin was especially active in inhibiting the growth of the common human pathogen Streptococcus pneumoniae, including strains resistant to conventional antibiotics. Plectasin has a low toxicity in mice, and cured them of peritonitis and pneumonia caused by S. pneumoniae as efficiently as vancomycin and penicillin, suggesting that it may have therapeutic potentia.

Now researchers lead by Prof. Dr. Hans-Georg Sahl of   Universities of Bonn, Utrecht, Aalborg and of the Danish company Novozymes AS have shed light on how the substance Plectasin,  destroy highly resistant bacteria. As per the claim by the researchers Plectasin binds to a cell-wall building block called lipid II and thus prevents it from being incorporated and thus disrupting the forming of the cell wall in bacteria so that the pathogens can no longer divide. 

In this process, plectasin behaves like a thief which steals the stones off a mason. 'It binds to a cell-wall building block called lipid II and thus prevents it from being incorporated ,' Professor Sahl explains. 'However, bacteria cannot live without a cell wall.' It comes as no surprise that the most famous antibiotic penicillin also inhibits cell-wall synthesis...

Researchers claims that, plectasin is more similar in its mode of action to another widely used drug, vancomycin. Vancomycin had been the drug of choice in combating MRSA strains since the 1980s. Meanwhile, though, there are more and more bacteria that are also resistant to vancomycin. 'However, these strains are still susceptible to plectasin,' Dr. Tanja Schneider emphasises. Nevertheless, there is no permanent solution to the resistance problem even with a new antibiotic . 'It is always just a question of time until the pathogens mutate and become insensitive ,' she says. 'It's a never ending arms race..' authors conclude that plectasin will be promising lead compound for new antibiotics...

Ref : http://www.sciencemag.org/cgi/content/abstract/328/5982/1168