There are two main types of bacteria, and these categories reflect the microbes' biology and their vulnerability to different antibiotics.

Gram-positive bacteria are bacteria that contain a thick cell wall. During the Gram staining process — a test that experts use to view the bacteria under a microscope — they appear purple or blue.

Characteristics of Gram-Positive Bacilli A gram-positive bacillus doesn't have an outer cell wall beyond the peptidoglycan membrane. This makes it more absorbent.