Cetocycline (formerly chelocardin or cetotetrine) is tetracycline derivative with potent antibacterial activity against a number of Gram-positive and Gram-negative multi-resistant pathogens. Cetocycline was found to be more active than tetracycline against many clinical isolates of aerobic gram-negative bacilli, but is less active against staphylococci, and has no activity against Pseudomonas. At low concentrations, like classical tetracyclines, chelocardin induces the proteomic signature for peptidyl transferase inhibition demonstrating that protein biosynthesis inhibition is the dominant physiological challenge. At higher concentrations B. subtilis mainly responds to membrane stress indicating that at clinically relevant concentrations the membrane is the main antibiotic target of chelocardin.