Lolamicin is an antibiotic specifically targeting Gram-negative bacteria. It is effective against over 130 multi-drug resistant clinical isolates, demonstrating efficacy in various mouse models of acute pneumonia and sepsis while preserving the mice's gut microbiota and preventing secondary infections from Clostridium difficile. Lolamicin's ability to selectively kill pathogenic Gram-negative bacteria results from the low sequence homology between pathogenic bacteria and symbiotic organisms. It is suitable for research on infections caused by Gram-negative pathogens.