Question

Anaerobes are resistant intrinsically against

• A. Beta lactam antibiotics
• B. Aminoglycosides
• C. Azithromycin
• D. Metronidazole

Answer 1

The Correct Option is B

Step 1: Think about how an antibiotic enters the bacterial cell. Aminoglycosides depend on an oxygen-requiring transport step to cross the membrane.
Step 2: Anaerobes, by definition, do not run an oxidative electron-transport chain. Without that energised uptake, aminoglycoside molecules stay outside and never reach the ribosome, so the bug is naturally unaffected.
Step 3: This is a classic example of intrinsic resistance, a built-in structural or functional trait of the organism rather than an acquired plasmid or mutation. Hence anaerobes are inherently resistant to aminoglycosides.
Step 4: Rule out the alternatives: metronidazole is actually the drug of choice for anaerobes, and beta-lactams and azithromycin retain useful activity against many anaerobic species, so they are not examples of intrinsic resistance here.
\[\boxed{Aminoglycosides}\]