English Reference

Word

bacteria

Phoneticsbac·te·ria

US/bækˈtɪɹiə/

UK/bæktˈiəɹɪɐ/

Definitions

01microorganisms

B2 · Science

n. tiny living things that can only be seen with a microscope.

n. microscopic single-celled organisms that exist in diverse environments. Technically the plural of 'bacterium', though frequently used as a collective noun in non-scientific contexts.

“You should wash your hands to get rid of any harmful bacteria.”

“The researchers identified several strains of bacteria in the soil that were capable of breaking down plastic waste.”

Usage

Usually plural; takes a plural verb in formal and academic writing.

Pitfall

This bacteria is very dangerous.

These bacteria are very dangerous.

In formal and scientific writing, 'bacteria' is plural. Use 'bacterium' for a single organism.

Synonyms

02a lowlife person

C2

n. a very rude or unpleasant person who is treated with no respect.

n. a derogatory term for a person or group of people perceived as socially or morally inferior.

“He treated the waiters like they were just bacteria.”

“The corrupt official looked down on the protesters as if they were mere bacteria infecting his city.”

Slang · Vulgar

Teaching tip

This is a highly offensive and dehumanising insult; learners should recognise it but avoid using it.

Synonyms

scumlowlifeslob

Real-World Examples

“On Earth, any life form more advanced than bacteria requires liquid water to survive.”
The Guardian · 11 Aug 2026
“Some people can carry bacteria in their nose or throat without getting sick, but can spread it to others.”
BBC News · 16 Jul 2026
“The AI models were trained on genetic codes from viruses, bacteria, plants and people.”
BBC News · 6 Aug 2026

Etymology

Borrowed from New Latin bacteria, plural of bactērium, from Ancient Greek βακτήριον (baktḗrion, “little rod”).

From New Latin bactēria, from Ancient Greek βακτηρίᾱ (baktēríā, “rod, stick”).

Etymology adapted from Wiktionary, available under CC BY-SA 4.0.

Related words

Domain

Medicine

This entry

Level
B2 · Upper Intermediate
Frequency
Common
Updated

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