Treating Gram-negative bacteria with antibiotics remains difficult due to the lack of a target that is specific for this population while sparing other innocuous groups. Broad spectrum antibiotics are known to affect gut microbiome diversity which can result in secondary Clostridioides difficile infections. The Lol system, which mediates lipoprotein transport between the inner and outer membranes in Gram-negative bacteria, is viewed as an enticing target. In particular, the transporter LolCDE is required for Gram-negative pathogen growth and exhibits low sequence homology with commensal bacteria. Now, Muñoz et al. have utilized known inhibitors of the LolCDE complex and modified them to improve their anti-bacterial activity against wild-type, Gram-negative pathogens, resulting in the development of the antibiotic lolamicin. Lolamicin exhibited strong activity against multidrug resistant isolates of Gram-negative pathogens such as Escherichia coli and Klebsiella pneumoniae but was inactive against Gram-positive pathogens and commensal bacteria, and was well-tolerated in mammalian cell lines and red blood cells. Generation of spontaneous lolamicin-resistant mutants in E. coli and K. pneumoniae revealed amino acid changes in LolC and LolE, confirming that lolamicin acts on the LolCDE complex. Docking and molecular dynamics simulations using the published cryo-electron microscopy structure of LolCDE identified four potential lolamicin binding clusters in the vicinity of the identified resistance mutations, suggesting that lolamicin may competitively block lipoprotein binding. Treatment of lolamicin in mice exhibited good oral bioavailability and tolerance and was effective against infections with antibiotic-resistant strains of K. pneumoniae. Compared with broad spectrum antibiotics, lolamicin treatment did not alter the gut microbiome diversity and prevented C. difficile infection. Overall, the work from Muñoz et al. reveals a potential strategy to treat a variety of Gram-negative infections with minimal off-target effects.

Original reference: Nature 629, 429–436 (2024)