ˌpenəˈsilə̇n noun
( -s )
Etymology: penicill- (from New Latin Penicillium ) + -in
1. : a mixture of antibiotic relatively nontoxic acids produced especially by molds of the genus Penicillium (as P. notatum or P. chrysogenum ) and having a powerful bacteriostatic effect against various bacteria (as staphylococci, gonococci, pneumococci, hemolytic streptococci, or some meningococci)
2. : any of numerous often hygroscopic and unstable amido acids that have the general formula RCONH(C 7 H 9 NOS)COOH and contain fused thiazolidine and beta-lactam rings in their structures and that are components of the penicillin mixture or are produced biosynthetically by the use of different strains of molds or different media or are synthesized chemically: as
a. or penicillin F also penicillin I : the first penicillin C 5 H 9 CONH(C 7 H 9 NOS)COOH isolated in Britain; 2-pentenyl-penicillin
b. or penicillin G also penicillin II : the penicillin C 6 H 5 CH 2 CONH(C 7 H 9 NOS)COOH that constitutes the principal or sole component of most commercial preparations and is used chiefly in the form of stable salts (as the crystalline sodium salt or the crystalline procaine salt) — called also benzylpenicillin
c. or penicillin V : a crystalline nonhygroscopic acid C 6 H 5 OCH 2 CONH(C 7 H 9 NOS)COOH that is produced biosynthetically and synthetically and that is similar to penicillin G in antibacterial action but is better absorbed by the gastrointestinal tract — called also phenoxymethylpenicillin
3. : a salt or ester of a penicillin acid or a mixture of such salts or esters