**Question:** An 18-year-old college freshman shares a dorm room with three roommates. One of his roommates has been diagnosed with meningococcal meningitis, caused by the bacteria Neisseria meningitidis. The other three roommates are isolated and treated twice a day with an antibiotic as prophylaxis against this organism, because none of them had received the meningococcal vaccine prior to enrollment. They are told that this antibiotic can give a reddish discoloration of their urine or tears. The reason this drug is effective in killing the bacteria is which one of the following?

A. It inhibits bacterial cell wall synthesis
B. It interferes with bacterial protein synthesis
C. It causes bacterial DNA degradation
D. It impairs bacterial respiratory function

**Correct Answer:**

**Core Concept:**

Meningococcal meningitis is an infection caused by the bacterium Neisseria meningitidis, which primarily affects the meninges (protective membranes) surrounding the brain and spinal cord. Antibiotics are used to treat and prevent bacterial infections, and the choice of antibiotic depends on the specific bacteria causing the infection. In this case, the antibiotic being used is effective against N. meningitidis, which is a gram-negative bacterium.

**Why the Correct Answer is Right:**

The antibiotic being used is effective against N. meningitidis because it inhibits bacterial cell wall synthesis. Gram-negative bacteria, like N. meningitidis, have a unique cell wall structure that is different from gram-positive bacteria. The cell wall is composed of lipopolysaccharides, peptidoglycan, and an outer membrane. Antibiotics targeting bacterial cell wall synthesis, such as penicillin, can effectively kill gram-negative bacteria like N. meningitidis.

**Why Other Options are Incorrect:**

A. Interfering with bacterial protein synthesis (Option B) is incorrect because N. meningitidis is a gram-negative bacterium, and antibiotics targeting protein synthesis are more effective against gram-positive bacteria.

C. Causing bacterial DNA degradation (Option C) is incorrect due to the same reason as option B. Antibiotics causing DNA degradation are more effective against gram-positive bacteria.

D. Impeding bacterial respiratory function (Option D) is incorrect because gram-negative bacteria, like N. meningitidis, have a unique respiratory system that is different from gram-positive bacteria. Antibiotics targeting respiratory function are more effective against gram-positive bacteria.