Using genome mining and heterologous expression, we report the discovery and production of a new antimicrobial lasso peptide from species related to the complex. Using NMR and mass spectrometric analysis, we show that this lasso peptide, named cloacaenodin, employs a threaded lasso fold which imparts proteolytic resistance that its unthreaded counterpart lacks. Cloacaenodin has selective, low micromolar, antimicrobial activity against species related to the complex, including species implicated in nosocomial infections and against clinical isolates of carbapenem-resistant . We further used site-directed mutagenesis to probe the importance of specific residues to the peptide's biosynthesis, stability, and bioactivity.