Bacteria, the plural form of the singular bacterium, is occasionally misapplied in formal writing. The key way to remember this is to look for a singular-plural disagreement with the verb "is" or "are". If you are using "is" it must always be paired with a singular noun, and vice versa. Examples of correct and incorrect applications of this can be found below: > [!check] *Streptococcus mutans* is a gram-positive bacterium[^1] > [!check] *Streptococcus mutans* and *Streptococcus pyogenes* are gram-positive bacteria > [!fail] *Streptococcus mutans* is a gram-positive bacteria Note that in each sentence, we can remove the descriptor (gram-positive) to check whether or not the sentence still sounds correct. And, before it comes up, [^1]: The cell envelope descriptor "gram" may be capitalized or lowercase. Its named after the scientist that developed the gram staining procedure, but is also commonly lowercased, so as long as your paper is consistent in its use either is acceptable.