QUICK ANSWER
"Bacteria" is a noun which is often translated as "bacterium", and "virus" is a noun which is often translated as "virus". Learn more about the difference between "bacteria" and "virus" below.
la bacteria(
bahk
-
teh
-
ryah
)A feminine noun is almost always used with feminine articles and adjectives (e.g., la mujer bonita, la luna llena).
1. (biology)
a. bacterium (formal) (singular)
A word or phrase used to refer to the second person formal “usted” by their conjugation or implied context (e.g., usted).
A word or phrase that is singular (e.g., el gato).
No han podido identificar la bacteria específica que le está causando los problemas estomacales a mi padre.They haven't been able to identify the specific bacterium responsible for my father's chronic stomach problem.
b. bacteria (plural)
A word or phrase that is plural (e.g., los libros).
Es importante no tomar antibióticos sin receta médica porque las bacterias podrían volverse resistentes a ellos.It's important not to take antibiotics without a doctor's prescription because the bacteria could become resistant to them.
c. germ
Niños, hay que lavarse las manos antes de comer para matar las bacterias.Kids, you have to wash your hands before eating to kill the germs.
el virus(
bee
-
roos
)A masculine noun is used with masculine articles and adjectives (e.g., el hombre guapo, el sol amarillo).
1. (medicine)
a. virus
Los virus pueden ser hasta 20 veces más pequeños que las bacterias.Viruses can be up to 20 times smaller than bacteria.
2. (computing)
a. virus
Recomiendo que compres este software para proteger tu laptop contra los virus.I recommend that you buy this software to protect your laptop against viruses.