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penicillin
(pen″ĭ-sil´in)
any of a large group of natural or semisynthetic antibacterial antibiotics derived directly or indirectly from strains of fungi of the genus Penicillium and other soil-inhabiting fungi grown on special culture media. Penicillins exert a bacteriocidal as well as a bacteriostatic
effect on susceptible bacteria by interfering with the final stages of the synthesis of peptidoglycan, a substance in the
bacterial cell wall. Despite their relatively low toxicity for the host, they are active against many bacteria, especially
gram-positive pathogens (streptococci, staphylococci, pneumococci); clostridia; certain gram-negative forms (gonococci and
meningococci); certain spirochetes (Treponema pallidum and T. pertenue); and certain fungi. Certain strains of some target species, for example staphylococci, secrete the enzyme penicillinase, which inactivates penicillin and confers resistance to the antibiotic. Some newer penicillins, such as methicillin, are more effective against penicillinase-producing organisms. A class of extended-spectrum penicillins includes piperacillin and mezlocillin.
penicillin G
the most widely used penicillin, used principally in the treatment of infections due to gram-positive organisms, gram-negative
cocci, Treponema pallidum and Actinomyces israelii. The usual forms are salts such as penicillin benzathine, potassium, procaine, or sodium. Called also benzylpenicillin.
penicillin V
a biosynthetically or semisynthetically produced antibiotic similar to penicillin g, used orally in the form of the benzathine or potassium salt for mild to moderately severe infections due to susceptible
gram-positive bacteria.
Copyright 2007. An Elsevier publication. All rights reserved.
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