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Peptidomimetic Antibiotics Target Outer-Membrane Biogenesis in Pseudomonas aeruginosa

Killing Pseudomonas Gram-negative Pseudomonas bacteria are opportunistic pathogens, and drug-resistant strains present a serious health problem. Srinivas et al. (p. 1010) synthesized a family of peptidomimetic antibiotics that is active only against Pseudomonas. These antibiotics do not lyse the cell membrane, but instead target an essential outer membrane protein, LptD, which plays a role in the assembly of lipopolysaccharide in the outer cell membrane. Activity in a mouse infection model suggests that the antibiotics might have therapeutic potential. In addition, LptD is widely distributed in gram-negative bacteria and so its validation as a target has the potential to drive development of antibiotics with a broader spectrum of activity against gram-negative pathogens. A synthesized antibiotic targets a protein involved in outer-membrane biogenesis to selectively kill Pseudomonas pathogens. Antibiotics with new mechanisms of action are urgently required to combat the growing health threat posed by resistant pathogenic microorganisms. We synthesized a family of peptidomimetic antibiotics based on the antimicrobial peptide protegrin I. Several rounds of optimization gave a lead compound that was active in the nanomolar range against Gram-negative Pseudomonas spp., but was largely inactive against other Gram-negative and Gram-positive bacteria. Biochemical and genetic studies showed that the peptidomimetics had a non–membrane-lytic mechanism of action and identified a homolog of the β-barrel protein LptD (Imp/OstA), which functions in outer-membrane biogenesis, as a cellular target. The peptidomimetic showed potent antimicrobial activity in a mouse septicemia infection model. Drug-resistant strains of Pseudomonas are a serious health problem, so this family of antibiotics may have important therapeutic applications.