How to say "bacteria" in Japanese

• バクテリアCommon
  nounA katakana borrowing that closely mirrors the English word; it covers bacteria as a general concept and works in both scientific explanation and everyday conversation.
  バクテリアはアルコールの中なかでは繁殖はんしょくしない。↗

  Bacteria will not breed in alcohol.
• 細菌さいきんJLPT N1approx.Common
  nounThe word you meet in science and medicine — biology lessons, hospital explanations, news about infections. It treats bacteria as a scientific category, covering a single bacterium or bacteria in general.
  この化学薬品かがくやくひんは細菌さいきんの繁殖はんしょくを防ふせぐだろう。↗

  This chemical will prevent germs from breeding.
• ばい菌ばいきんJLPT N1approx.Common
  nounEveryday 'germs': the unwelcome things on hands and food that hand-washing and cleaning target. It really means germs or bugs, so for bacteria in the scientific sense it is only a loose stand-in.

For bacteria as a scientific concept choose 細菌, or 「バクテリア」 when the English-like loanword fits; reserve 「ばい菌」 for everyday germs and bugs, not scientific talk.

Usage comparisons are AI-assisted and cross-checked by multiple models; for study reference only

• バクテリアbacteria
• 細菌さいきんbacterium
• ばい菌ばいきんgerm
• 真正細菌しんせいさいきんbacteria
• 細菌類さいきんるいbacteria