Penicillin would be most effective against which type of bacteria?

• A. Gram-positive bacteria
• B. Gram-negative bacteria
• C. Mycoplasma species
• D. Archaea

Answer: (A)

Verified step by step guidance

1. Step 1: Understand the mechanism of action of penicillin. Penicillin works by inhibiting the synthesis of peptidoglycan, an essential component of the bacterial cell wall.
2. Step 2: Recall the structural differences between Gram-positive and Gram-negative bacteria. Gram-positive bacteria have a thick peptidoglycan layer, while Gram-negative bacteria have a thinner peptidoglycan layer but possess an outer membrane that can block some antibiotics.
3. Step 3: Consider why penicillin is more effective against Gram-positive bacteria. Since Gram-positive bacteria have a thick peptidoglycan layer exposed on the surface, penicillin can easily target and disrupt their cell wall synthesis.
4. Step 4: Note that Mycoplasma species lack a cell wall entirely, so penicillin, which targets cell wall synthesis, is ineffective against them.
5. Step 5: Recognize that Archaea have different cell wall compositions that do not contain peptidoglycan, making penicillin ineffective against them as well.