Which of the following characteristics is a reason why a gram-stain to distinguish gram-positive from gram-negative bacteria is an important tool in a medical diagnosis of a bacterial infection?

- all of the listed characteristics are reasons why a gram-stain is important in medicine.
- the outer membrane of a gram-negative bacterium protect it from the body's defenses.
- certain gram-positive bacteria are resistant to antibiotics.
- the cell walls of many gram-negative bacteria are toxic.
- none of the listed characteristics is a reason why a gram-stain is important in medicine.