pen·​i·​cil·​lin | \ ˌpe-nə-ˈsi-lən How to pronounce penicillin (audio) \

Definition of penicillin

1 : any of several relatively nontoxic antibiotic acids of the general formula C9H11N2O4SR that are produced by molds (genus Penicillium and especially P. notatum or P. chrysogenum) or synthetically and are used especially against gram-positive cocci also : a mixture of such acids
2 : a salt or ester of a penicillin or a mixture of such salts or esters

Examples of penicillin in a Sentence

Recent Examples on the Web There were others: Barbara Low, one of the few women in scientific research in the 1940s, advanced our understanding of penicillin, leading to a cornucopia of antibiotics that continue to save lives. William Mcdonald, New York Times, "In a Year of Notable Deaths, a World of Women Who Shattered Ceilings," 26 Dec. 2019 It's been almost a century since the discovery of penicillin kicked off the era of antibiotics. David Freeman, NBC News, "Antibiotics are losing their power against deadly infections. Can we fix the problem?," 10 Oct. 2019 Nearly half of bacteria gathered in public settings around the city were resistant to two or more commonly used antibiotics, like penicillin and erythromycin. Christopher Intagliata reports. Christopher Intagliata, Scientific American, "London Crawling with Drug-Resistant Microbes," 3 Aug. 2019 Currently, strep throat is not resistant to common first-line antibiotics such as penicillin or amoxicillin. Anchorage Daily News, "Deadly superbugs pose greater threat than previously estimated," 13 Nov. 2019 Elortegui said the mold involved is of the same family as penicillin. al, "Mold cleanup a ‘massive undertaking’ in Mobile Saenger," 27 Sep. 2019 Some of those drugs include penicillin, Prozac, Zyprexa and Humulin. Shari Rudavsky, Indianapolis Star, "Lilly to announce $400M investment in Indianapolis manufacturing along with new jobs," 20 Nov. 2019 But by the 1940s, penicillin was found to have a near-perfect cure rate for the disease. Los Angeles Times, "1,306 U.S. infants were born with syphilis in 2018, even though it’s easy to prevent," 8 Oct. 2019 Many harmful bacteria have evolved to evade antibiotics in the 91 years since the first such medicine, penicillin, was extracted from a fungus. oregonlive, "Twice as many killed by antibiotic-resistant bacteria than thought, feds say, but infections overall are falling," 13 Nov. 2019

These example sentences are selected automatically from various online news sources to reflect current usage of the word 'penicillin.' Views expressed in the examples do not represent the opinion of Merriam-Webster or its editors. Send us feedback.

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First Known Use of penicillin

1929, in the meaning defined at sense 1

History and Etymology for penicillin

New Latin Penicillium

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Time Traveler for penicillin

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The first known use of penicillin was in 1929

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Last Updated

15 Jan 2020

Cite this Entry

“Penicillin.” The Dictionary, Merriam-Webster Inc., Accessed 26 January 2020.

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How to pronounce penicillin (audio)

English Language Learners Definition of penicillin

: a medicine that is used to kill harmful bacteria


pen·​i·​cil·​lin | \ ˌpe-nə-ˈsi-lən How to pronounce penicillin (audio) \

Kids Definition of penicillin

: an antibiotic that is produced by a mold and is used against disease-causing bacteria


pen·​i·​cil·​lin | \ ˌpen-ə-ˈsil-ən How to pronounce penicillin (audio) \

Medical Definition of penicillin

1 : a mixture of relatively nontoxic antibiotic acids produced especially by molds of the genus Penicillium (as P. notatum or P. chrysogenum) and having a powerful bacteriostatic effect against various chiefly gram-positive bacteria (as staphylococci, gonococci, pneumococci, hemolytic streptococci, or some meningococci)
2 : any of numerous often hygroscopic and unstable amido acids (as penicillin G, penicillin O, and penicillin V) that have a structure in which a four-membered lactam ring shares a nitrogen and a carbon atom with a thiazolidine ring to which it is fused 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
3 : a salt or ester of a penicillin acid or a mixture of such salts or esters

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More from Merriam-Webster on penicillin

Spanish Central: Translation of penicillin

Nglish: Translation of penicillin for Spanish Speakers Encyclopedia article about penicillin

Comments on penicillin

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to express in a more acceptable way

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