Plates that have only ampicillin-resistant bacteria growing include which of the following?

• A. Plates containing both ampicillin and tetracycline
• B. Plates containing tetracycline as the only antibiotic
• C. Plates containing ampicillin as the only antibiotic
• D. Plates containing no antibiotics

Answer: (C)

Verified step by step guidance

1. Step 1: Understand the concept of antibiotic resistance. Bacteria that are resistant to a specific antibiotic can grow on plates containing that antibiotic, while sensitive bacteria cannot.
2. Step 2: Analyze the plates containing both ampicillin and tetracycline. Only bacteria resistant to both antibiotics would grow here, so plates with only ampicillin-resistant bacteria would not grow on these plates.
3. Step 3: Consider plates containing tetracycline as the only antibiotic. Bacteria resistant only to ampicillin would not grow here because tetracycline is present and they are not resistant to it.
4. Step 4: Look at plates containing ampicillin as the only antibiotic. Bacteria resistant to ampicillin can grow here, so these plates would show growth of ampicillin-resistant bacteria.
5. Step 5: Evaluate plates containing no antibiotics. All bacteria, resistant or not, can grow here, so these plates do not specifically indicate ampicillin resistance.