In Search of New Antibiotics
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A team of researchers at the University of Wisconsin-Madison (my alma mater) genetically engineered a strain of Streptomyces platensis to overproduce the antibiotics platensimycin and platencin. They accomplished this by deleting a regulatory gene (ptmR1, whichencodes a putative GntR-like transcriptional regulator) in the antibiotic synthetic pathway that controls production. The newly engineered strain has been reported to overproduce platensimycin and platencin with yieldsof 323 ± 29 mg/L and 255 ± 30 mg/L, respectively. This represents a 100-fold increase in the yields observed with corresponding S. platensis wild type strains.
Platensimycin is the first of a new class of natural product antibiotics (with a novel mode of action) to be discovered in the past 40 years. It exhibits strong, broad-spectrum Gram-positive antibacterial activity by selectively inhibiting cellular lipid biosynthesis. Treatment with platensimycin eradicates Staphylococcus aureus infection in mice. Because of its unique mode of action, platensimycin shows no cross-resistance to other key antibiotic-resistant strains tested, including methicillin-resistant S. aureus, vancomycin-intermediate S. aureus and vancomycin-resistant enterococci.
Platencin, also a natural product, is chemically and biologically related but different from platensimycin. Like platensimycin, it exhibits a broad-spectrum Gram-positive antibacterial activity through inhibition of fatty acid biosynthesis. And, it doesn’t exhibit cross-resistance to methicillin-resistant Staphylococcus aureus, vancomycin-intermediate S. aureus, and vancomycin-resistant Enterococci. Moreover, platencin shows potent in vivo efficacy without any observed toxicity.
Both antibiotics show promise for commercialization. While we need new antibiotics, both platensimycin and platencin target only Gram positive bacteria. Infections caused by multiple drug resistant Gram negative bacteria are threatening to overtake those caused by Gram positive in the very near future. At present, to the best of my knowledge, there are no new antibiotics in the pipeline directed against multiple drug resistant Gram negative strains.
Until next time...
Good Luck and Good Antibiotic Hunting!!!!!!!!
