mecillinam antibiotic_resistance Mecillinam is a broad-spectrum beta-lactam antibiotic that was semi-synthetically derived to have a different drug centre, being a 6-alpha-amidinopenicillanate instead of a 6-alpha-acylaminopenicillanate. Contrasting most beta-lactam drugs, mecillinam is most active against Gram-negative bacteria. It binds specifically to penicillin binding protein 2 (PBP2). ChEBI:51208 Selexidin Selexid CAS:32887-01-7 ChEMBL:CHEMBL530 ARO:3000761 amdinocillin PubChem:36273 penicillin with extended spectrum