Which of the following statements are true?
i. Bacterial ribosomes are a good target for selective toxicity because they differ from human ribosomes.
ii. Most antimicrobials that inhibit protein synthesis are broad-spectrum.
iii. The large majority of drugs that affect the ribosome bind to the 50s subunit, as that is where peptide bond formation occurs.

• A. I & II.
• B. I & III.
• C. II & III.
• D. I, II, & III

Answer: (A)

Verified step by step guidance

1. Step 1: Understand the concept of selective toxicity in antimicrobial therapy, which relies on targeting structures or processes unique to bacteria, such as bacterial ribosomes, which differ from human ribosomes. This makes statement i plausible.
2. Step 2: Consider the spectrum of antimicrobials that inhibit protein synthesis. Many of these drugs affect a wide range of bacteria, making them broad-spectrum agents, which supports statement ii.
3. Step 3: Analyze the ribosomal subunits and their functions. The bacterial ribosome consists of 30S and 50S subunits. Peptide bond formation occurs at the 50S subunit, so many drugs targeting protein synthesis bind here, which relates to statement iii.
4. Step 4: Evaluate each statement based on microbiological knowledge: statement i is true because bacterial ribosomes differ from human ones; statement ii is generally true as many protein synthesis inhibitors are broad-spectrum; statement iii is partially true but requires careful consideration of which drugs bind to which subunit.
5. Step 5: Compare the statements and select the correct combination of true statements based on the above analysis.