Biotransformation of Antibiotics - Biotransformation is routinely used for commercial production of several useful antibiotics. Semisynthetic antibiotics, e.g., semisynthetic penicillin and cephalosporins, are produced by chemical modification of the penicillin nucleus, e.g., 6-aminopenicillanic acid. The penicillin nucleus is produced by microbial deacylation of naturally produced penicillin G and penicillin V.