How Does Streptomycin Attack Bacterial Cells?

Streptomycin, a powerful antibiotic, plays a critical role in fighting bacterial infections by specifically targeting bacterial cells.

Here you will learn how streptomycin functions, its mechanism of action, and why it’s effective against certain bacteria.

What Is Streptomycin?

Streptomycin is an aminoglycoside antibiotic derived from the bacterium Streptomyces griseus. It is primarily used to treat infections caused by Gram-negative bacteria, including tuberculosis and plague.

Its mechanism of action revolves around disrupting bacterial protein synthesis.

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Mechanism of Action: How Streptomycin Attacks Bacterial Cells

Targeting the Ribosome

Streptomycin exerts its effect by binding to the 30S subunit of the bacterial ribosome. This binding causes significant disruptions in the protein synthesis process, which is crucial for bacterial growth and survival.

1. Binding to the 30S Subunit
   • Streptomycin binds irreversibly to the 30S ribosomal subunit of prokaryotic cells.
   • This prevents the accurate translation of messenger RNA (mRNA).
2. Misreading of Genetic Code
   • The drug forces the ribosome to misread the mRNA sequence.
   • Incorrect amino acids are incorporated into the polypeptide chain, resulting in faulty or nonfunctional proteins.
3. Inhibition of Protein Synthesis
   • By disrupting protein production, streptomycin halts essential cellular processes, leading to bacterial death.
   • This makes streptomycin bactericidal rather than bacteriostatic.

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Why Streptomycin Doesn’t Affect Human Cells

Streptomycin is selective for bacterial cells because human cells have a different type of ribosome. While bacterial ribosomes are 70S (composed of 30S and 50S subunits), human ribosomes are 80S.

This structural difference ensures that streptomycin specifically targets bacterial protein synthesis without harming human cells.

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What Types of Bacteria Does Streptomycin Target?

Effective Against Gram-Negative Bacteria

Streptomycin is especially potent against Gram-negative bacteria due to its ability to penetrate their cell walls. Examples include:

• Escherichia coli (E. coli)
• Klebsiella pneumoniae
• Yersinia pestis (plague-causing bacteria)

Limited Activity Against Gram-Positive Bacteria

While streptomycin can act against certain Gram-positive bacteria, its efficacy is more pronounced with Gram-negative organisms.

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Resistance to Streptomycin: A Growing Concern

How Bacteria Develop Resistance

Bacterial resistance to streptomycin can arise due to:

• Mutation of the 30S Ribosomal Subunit: Structural changes prevent streptomycin from binding effectively.
• Efflux Pumps: Some bacteria develop mechanisms to pump the antibiotic out of the cell.
• Enzymatic Inactivation: Enzymes such as aminoglycoside-modifying enzymes can deactivate streptomycin.

Combating Resistance

To reduce resistance, streptomycin is often used in combination with other antibiotics.

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Side Effects and Considerations

While streptomycin is effective, it’s not without side effects. These may include:

• Ototoxicity: Hearing loss or tinnitus.
• Nephrotoxicity: Kidney damage.
• Neuromuscular Blockade: Rare but possible, leading to muscle weakness.

Due to these risks, streptomycin use is typically reserved for severe infections under medical supervision.

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FAQs

1. How does streptomycin differ from other antibiotics?

Streptomycin specifically targets the 30S ribosomal subunit, while other antibiotics may inhibit cell wall synthesis or DNA replication.

2. Can streptomycin treat viral infections?

No, streptomycin is ineffective against viruses because it targets bacterial ribosomes, which viruses lack.

3. How is streptomycin administered?

It is typically administered via intramuscular injection or intravenously in severe infections.