bacteria
The Spanish word 'bacteria' translates directly to 'bacteria' in English. It is a type of biological cell. They constitute a large domain of prokaryotic microorganisms. Bacteria were among the first life forms to appear on Earth, and are present in most of its habitats.
Bacteria are invisible to the naked eye.
This sentence emphasizes on the fact that one cannot see bacteria without the use of microscope or other similar tools.
Bacteria can cause an infection.
This sentence is describing one of the possible harmful effects of bacteria, which is the ability to cause infections in living organisms.
A bacteria is needed to ferment milk.
This sentence illustrates one of the useful purposes of bacteria, which is in the fermentation process of milk to produce dairy products like yogurt.