Peptide-Modified Antibiotic Fights Back Against Nearly Untreatable Drug-Resistant Bacteria

Peptide-linked amikacin conjugates showed powerful synergy with polymyxin B against extensively drug-resistant and pandrug-resistant Klebsiella pneumoniae. Of 31 resistant strains tested, 77% showed synergy when peptide-amikacin conjugates containing tryptophan and cysteine were combined with polymyxin B, including strains carrying multiple resistance enzymes (AMEs and RMTases). The peptide-linked compounds maintained similar mammalian cell toxicity as unmodified amikacin but were dramatically more synergistic with polymyxin B against resistant bacteria.

Researchers chemically synthesized a library of peptide-linked amikacin derivatives, attaching amino acids with different properties (positively charged, sulfur-containing, or aromatic side chains). These conjugates were tested alone and in combination with polymyxin B against 31 Klebsiella pneumoniae strains with various resistance mechanisms. Synergy was assessed using standard antimicrobial susceptibility testing, and mammalian cell toxicity was evaluated.

Drug-resistant Klebsiella pneumoniae is at the top of the WHO's critical priority pathogen list, and existing antibiotics are rapidly losing effectiveness. By linking amino acid peptides to the antibiotic amikacin, researchers created a new class of conjugates that restore antibiotic activity against bacteria that are resistant to virtually everything. This peptide-modification strategy could be a lifeline against the growing threat of untreatable infections.

Antimicrobial resistance is projected to cause millions of deaths annually if new solutions aren't found. This study demonstrates that peptide conjugation — attaching peptide fragments to existing antibiotics — can overcome even the most extreme resistance mechanisms. It's part of a broader trend in peptide-antibiotic hybrid drug design that could extend the useful life of our existing antibiotic arsenal.

This is an in vitro study; the peptide-amikacin conjugates have not been tested in animal models or humans. Pharmacokinetic properties (absorption, distribution, metabolism) of the conjugates are unknown. The study focused on Klebsiella pneumoniae — activity against other critical priority pathogens needs testing. The combination still requires polymyxin B, which has its own toxicity concerns.