peptide antibiotic oncocin ARO:3007748 PubChem:46889826 antibiotic_resistance ChEMBL:CHEMBL1083466 The small proline-rich antimicrobial peptide, oncocin, selectively targets Gram-negative bacteria through special transporters such as SmbA to enter cytoplasm. It presents low toxicity to mammalian cells, because they cannot effectively penetrate the mammalian cellular membrane or they are internalized through an endocytotic process to minimize interaction with cytosolic ribosomes.