Is Bacteria Plural or Singular? Understanding Grammatical Number in Microbiology

Bacterium and Bacteria — See the Pattern

Look at these sentences. Can you see the pattern?

• One bacterium was found in the water.
• Many bacteria live in your stomach.
• The bacterium is too small to see.
• These bacteria are not dangerous.

Did you notice? When we talk about one, we say bacterium. When we talk about more than one, we say bacteria. The ending changes from -um to -a.

This word comes from Latin. In Latin, many words that end in -um change to -a for plural. Here are more examples:

When to Use Bacterium and When to Use Bacteria

The rule is simple:

• Use bacterium when you talk about one: “This bacterium is harmless.”
• Use bacteria when you talk about more than one: “These bacteria are harmless.”

Because bacteria is plural, it always goes with plural verbs like are, were, have, and do. Because bacterium is singular, it goes with is, was, has, and does.

Easy way to remember: Think of the letters. BacteriUM = one (UM sounds like “hmm, just one”). BacteriA = a lot (A for “all of them”).

Real-Life Examples With Bacteria and Bacterium

Here are sentences you might hear in everyday life:

• The bacteria in yogurt are good for your stomach. (= more than one, so we use “are”)
• A single bacterium is too small to see without a special tool. (= just one, so we use “is”)
• Harmful bacteria can make you sick if you eat old food. (= more than one)
• Scientists found a new bacterium in the ocean last year. (= they found one)
• Millions of bacteria live on your skin right now. (= many, many more than one)

You are doing great. Now let us look at the mistakes many learners make.

Three Mistakes to Avoid With Bacteria

Even native English speakers get confused by bacteria and bacterium. If you mix them up sometimes, you are not alone.

Mistake 1: Adding -s to make “bacterias”

“Bacteria” is already plural. You do not need to add -s. The word “bacterias” does not exist in English.

Mistake 2: Using “bacteria” as singular

Many people say “a bacteria” or “the bacteria is.” But bacteria is plural, so it needs a plural verb.

How to remember: If you can say “many” or “these” before the word, it is plural. You say “many bacteria” and “these bacteria” — so bacteria is always plural. For one, switch to bacterium.

Other words like this: medium → media, datum → data, curriculum → curricula, fungus → fungi. They all come from Latin and follow old plural rules.

Test Yourself: Bacterium or Bacteria?

Choose an answer to see your feedback immediately. Your first answer counts towards your score.

Keep Going — You Are Building Something

You just learned the difference between bacterium and bacteria. That is one more Latin plural you will never get wrong again.

Use the examples above to practise this pattern. When you are ready, choose your next topic below.

Related Lesson for Review: What Is the Plural of Fungus?

Source

bacteria. wiktionary

Origin of bacteria

Khamis Maiouf

I’m Khamis Maiouf. I’m studying Health and Social Care and have completed Functional Skills Level 2 in English and Level 3 Hairdressing. I have taught ESOL in my community and helped students with GCSE English. I run English Teacher Site to help people learn and practise English.