Introduction: Streptomycin is a landmark aminoglycoside antibiotic with a distinctive structure composed of an aminocyclitol (streptidine) linked to sugar moieties (streptose and N‑methyl‑L‑glucosamine). Its mechanism of action involves binding the 30S ribosomal subunit at the decoding A‑site, causing misreading of mRNA, inhibition of initiation and eventual bactericidal killing. Key clinical and safety topics include spectrum (aerobic gram‑negatives, mycobacteria), oxygen‑dependent uptake, resistance mechanisms (enzymatic modification, rpsL/16S rRNA mutations, efflux), and toxicities (ototoxicity, nephrotoxicity). Understanding streptomycin’s chemistry, pharmacology and molecular action is essential for B.Pharm students. Now let’s test your knowledge with 30 MCQs on this topic.
Q1. Which antibiotic class does streptomycin belong to?
- Tetracyclines
- Aminoglycosides
- Macrolides
- Fluoroquinolones
Correct Answer: Aminoglycosides
Q2. Which structural moiety is characteristic of streptomycin?
- Beta‑lactam ring
- Streptidine (aminocyclitol) core
- Macrocyclic lactone
- Fluorinated quinolone nucleus
Correct Answer: Streptidine (aminocyclitol) core
Q3. Streptomycin primarily binds to which ribosomal subunit?
- 50S ribosomal subunit
- Mitochondrial 28S subunit
- 30S ribosomal subunit
- Peptidyl transferase center
Correct Answer: 30S ribosomal subunit
Q4. The key molecular effect of streptomycin on protein synthesis is:
- Inhibition of peptidyl transferase activity
- Prevention of tRNA charging by aminoacyl‑tRNA synthetases
- Induction of mRNA misreading and mistranslation
- Blocking ribosomal exit tunnel
Correct Answer: Induction of mRNA misreading and mistranslation
Q5. Streptomycin’s antibacterial effect is best described as:
- Bacteriostatic
- Bactericidal
- Bacteriolytic only in presence of penicillin
- Fungistatic
Correct Answer: Bactericidal
Q6. Uptake of streptomycin into bacterial cells is primarily:
- Passive diffusion through porins
- Energy (oxygen) dependent active transport
- Facilitated diffusion via carrier proteins
- Endocytosis‑like vesicular uptake
Correct Answer: Energy (oxygen) dependent active transport
Q7. A common resistance mechanism to streptomycin involves:
- Mutation in DNA gyrase
- Enzymatic modification by aminoglycoside‑modifying enzymes
- Inhibition of beta‑lactamases
- Increased expression of peptidoglycan
Correct Answer: Enzymatic modification by aminoglycoside‑modifying enzymes
Q8. One frequent genetic change conferring high‑level streptomycin resistance is mutation in:
- rpoB gene encoding RNA polymerase
- rpsL gene encoding ribosomal protein S12
- gyrA gene encoding DNA gyrase
- murA gene for cell wall synthesis
Correct Answer: rpsL gene encoding ribosomal protein S12
Q9. Streptomycin has historically been important in the treatment of:
- Uncomplicated urinary tract infections only
- Tuberculosis (as a second‑line or historical agent)
- Viral respiratory infections
- Fungal meningitis
Correct Answer: Tuberculosis (as a second‑line or historical agent)
Q10. The preferred routes of administration for streptomycin are:
- Oral tablets
- Topical cream
- Intramuscular or intravenous injection
- Inhalation aerosol
Correct Answer: Intramuscular or intravenous injection
Q11. The major dose‑limiting toxicities associated with streptomycin include:
- Hepatotoxicity and pancreatitis
- Ototoxicity and nephrotoxicity
- Bone marrow suppression and rash
- Cardiotoxicity and QT prolongation
Correct Answer: Ototoxicity and nephrotoxicity
Q12. At low concentrations streptomycin primarily interferes with which step of bacterial protein synthesis?
- Initiation complex formation
- Termination factor binding
- Ribosomal recycling
- Peptide bond formation
Correct Answer: Initiation complex formation
Q13. Streptomycin shows best activity against which organisms?
- Anaerobic gram‑positive cocci
- Aerobic gram‑negative bacilli and Mycobacteria
- Intracellular atypical bacteria only
- Fungi and protozoa
Correct Answer: Aerobic gram‑negative bacilli and Mycobacteria
Q14. Streptomycin is commonly used synergistically with which antibiotic class to improve clinical outcomes?
- Macrolides
- Beta‑lactams (cell wall inhibitors)
- Glycopeptides alone
- Sulfonamides only
Correct Answer: Beta‑lactams (cell wall inhibitors)
Q15. Why are anaerobic bacteria typically resistant to streptomycin?
- They express high levels of porins
- Lack of oxygen prevents uptake via the energy‑dependent transport
- They overproduce peptidoglycan
- They methylate the drug extracellularly
Correct Answer: Lack of oxygen prevents uptake via the energy‑dependent transport
Q16. Major sugar components present in streptomycin’s structure include:
- Glucose only
- Ribose and deoxyribose
- Streptose and N‑methyl‑L‑glucosamine attached to streptidine
- Sialic acid and galactose
Correct Answer: Streptose and N‑methyl‑L‑glucosamine attached to streptidine
Q17. Streptomycin’s killing kinetics are best described as:
- Time‑dependent killing with no post‑antibiotic effect
- Concentration‑dependent killing with a post‑antibiotic effect
- Neither concentration‑ nor time‑dependent
- Only effective when continuously infused
Correct Answer: Concentration‑dependent killing with a post‑antibiotic effect
Q18. The molecular basis of aminoglycoside‑induced ototoxicity is primarily attributed to:
- Direct inhibition of cochlear blood flow only
- Free radical formation and hair cell apoptosis in the inner ear
- Immune complex deposition in auditory nerve
- Blockade of acoustic neurotransmitter release
Correct Answer: Free radical formation and hair cell apoptosis in the inner ear
Q19. Aminoglycoside‑modifying enzymes include which of the following types?
- Acetyltransferases
- Adenylyltransferases (nucleotidyltransferases)
- Phosphotransferases
- All of the above
Correct Answer: All of the above
Q20. Streptomycin primarily affects which site in the ribosome decoding process?
- Peptidyl (P) site
- Aminoacyl (A) site / decoding center of 16S rRNA
- Exit (E) site
- 50S peptidyl transferase center
Correct Answer: Aminoacyl (A) site / decoding center of 16S rRNA
Q21. Which laboratory method is commonly used to determine bacterial susceptibility to streptomycin?
- Gram staining
- MIC determination by broth microdilution
- Nitrate reduction test
- Coagulase test
Correct Answer: MIC determination by broth microdilution
Q22. Oral administration of streptomycin is ineffective because:
- It is extensively metabolized by gut flora to inactive forms
- It is poorly absorbed from the gastrointestinal tract
- It causes immediate severe mucosal ulceration
- It converts to an active topical agent only
Correct Answer: It is poorly absorbed from the gastrointestinal tract
Q23. Chemically, streptomycin is best described as:
- A polyketide macrolide
- An aminocyclitol (streptidine) linked to amino sugars
- A glycopeptide antibiotic
- A lipopeptide
Correct Answer: An aminocyclitol (streptidine) linked to amino sugars
Q24. One proposed downstream effect of streptomycin‑induced mistranslation that contributes to bactericidal activity is:
- Increased DNA repair fidelity
- Insertion of defective membrane proteins that increase membrane permeability
- Stimulation of capsule synthesis
- Enhanced biofilm formation
Correct Answer: Insertion of defective membrane proteins that increase membrane permeability
Q25. The primary route of elimination for streptomycin is:
- Hepatic metabolism with biliary excretion
- Renal excretion of unchanged drug
- Metabolism by intestinal enzymes
- Exhalation via lungs
Correct Answer: Renal excretion of unchanged drug
Q26. Which organism is typically intrinsically resistant to streptomycin due to lack of oxygen‑dependent uptake?
- Pseudomonas aeruginosa
- Bacteroides fragilis (anaerobe)
- Mycobacterium tuberculosis
- Enterococcus faecalis
Correct Answer: Bacteroides fragilis (anaerobe)
Q27. Therapeutic drug monitoring for streptomycin is recommended because clinicians should monitor:
- Peak and trough serum concentrations to avoid toxicity
- Liver enzyme levels only
- Coagulation profile exclusively
- Fecal drug levels
Correct Answer: Peak and trough serum concentrations to avoid toxicity
Q28. In enterococcal endocarditis, streptomycin is used synergistically with a cell wall agent primarily because:
- The combination prevents renal toxicity
- Beta‑lactam or glycopeptide facilitates aminoglycoside entry resulting in bactericidal synergy
- The drugs share the same binding site on the ribosome
- It reduces the need for surgical valve replacement
Correct Answer: Beta‑lactam or glycopeptide facilitates aminoglycoside entry resulting in bactericidal synergy
Q29. Streptomycin can damage human mitochondria because mitochondrial ribosomes:
- Are identical to bacterial 50S subunits
- Resemble bacterial 30S subunits and can be inhibited by aminoglycosides
- Are resistant to all antibiotics
- Are protected by mitochondrial membranes from drug entry
Correct Answer: Resemble bacterial 30S subunits and can be inhibited by aminoglycosides
Q30. Streptomycin’s historical significance includes being:
- The first orally effective aminoglycoside
- The first antibiotic shown to be effective against tuberculosis
- A synthetic fluorinated antimicrobial discovered in the 1990s
- A topical antifungal agent
Correct Answer: The first antibiotic shown to be effective against tuberculosis
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