ba·​cil·​lus | \ bə-ˈsi-ləs How to pronounce bacillus (audio) \
plural bacilli\ bə-​ˈsi-​ˌlī How to pronounce bacilli (audio) also  -​lē \

Definition of bacillus

1 : any of a genus (Bacillus) of rod-shaped gram-positive usually aerobic bacteria producing endospores and including many saprophytes and some parasites (such as B. anthracis of anthrax) broadly : a straight rod-shaped bacterium
2 : bacterium especially : a disease-producing bacterium

Examples of bacillus in a Sentence

Recent Examples on the Web Centuries later, scientists concluded that the disease was caused by the bacillus , which spread through touch, through the air and through the bite of infected fleas and rats. Los Angeles Times, "This champion academic decathlon team studied pandemics. Now, they’re living one," 26 Mar. 2020 The results found all types of bacteria, like staphylococcus, streptococcus, bacillus cereus, and E. coli. Danielle Tullo, House Beautiful, "6 Places Germs Are Hiding In Your House," 11 Oct. 2018 According to NBC News, researchers announced Thursday that the bacillus Calmette-Guérin (BCG) vaccine has been shown, in a small group of study participants, to bring blood sugar levels down. Daniel Wilson, sacbee, "Study shows tuberculosis vaccine may reverse Type 1 diabetes," 21 June 2018 The study, published Thursday in the journal npj Vaccines by researchers at Massachusetts General Hospital, looked at nine people with type 1 diabetes who were given a vaccine to prevent tuberculosis, called bacillus Calmette-Guérin (BCG). Alexandra Sifferlin, Time, "There’s Hope for a Vaccine to Prevent Type 1 Diabetes," 21 June 2018 The study relied on the bacillus Calmette-Guérin (BCG) vaccine, which has been used in humans since 1921. Glenn Fleishman, Fortune, "Tuberculosis Vaccine Could Reverse Type 1 Diabetes, Study Shows," 21 June 2018 The team at Massachusetts General Hospital has been testing the bacillus Calmette-Guérin (BCG) vaccine, used to prevent tuberculosis and to treat some forms of bladder cancer. NBC News, "Can a cheap and widely available TB vaccine help diabetics?," 21 June 2018 According to the new research published in the journal npj Vaccines, a common vaccine for tuberculosis (the bacillus Calmette-Guérrin, or BCG, vaccine) could reverse advanced cases of the disease by permanently lowering blood sugar levels. Fiza Pirani, ajc, "Common vaccine may reverse advanced diabetes cases, study finds," 21 June 2018 Renovations can be observed in older buildings that in Soviet times were factories for mass-producing bacillus anthracis, the bacteria that causes anthrax. Joby Warrick,, "Poisoning of Russian ex-spy puts spotlight on Moscow's secret military labs," 18 Mar. 2018

These example sentences are selected automatically from various online news sources to reflect current usage of the word 'bacillus.' 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 bacillus

1868, in the meaning defined at sense 1

History and Etymology for bacillus

New Latin, from Medieval Latin, small staff, rod, diminutive of Latin baculus staff, alteration of baculum

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The first known use of bacillus was in 1868

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Last Updated

29 Mar 2020

Cite this Entry

“Bacillus.” Dictionary, Merriam-Webster, Accessed 30 Mar. 2020.

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How to pronounce bacillus (audio)

English Language Learners Definition of bacillus

technical : a straight rod-shaped bacterium that requires oxygen for growth also : a bacterium that causes disease


ba·​cil·​lus | \ bə-ˈsil-əs How to pronounce bacillus (audio) \
plural bacilli\ -​ˌī also -​ē \

Medical Definition of bacillus

1a capitalized : a genus of rod-shaped gram-positive endospore-producing usually aerobic bacteria of the family Bacillaceae that include many saprophytes and some parasites (as B. anthracis of anthrax)
b : any bacterium of the genus Bacillus broadly : a straight rod-shaped bacterium
2 : bacterium especially : a disease-producing bacterium

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More from Merriam-Webster on bacillus

Rhyming Dictionary: Words that rhyme with bacillus

Spanish Central: Translation of bacillus

Nglish: Translation of bacillus for Spanish Speakers

Britannica English: Translation of bacillus for Arabic Speakers Encyclopedia article about bacillus

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