What is the Difference Between Aminoglycosides and Tetracyclines

The main difference between aminoglycosides and tetracyclines is that aminoglycosides are bactericidal and kill bacteria whereas tetracyclines are bacteriostatic and stop the reproduction of bacteria.

Aminoglycosides and tetracyclines are two types of antibiotics that inhibit the protein synthesis of bacteria. Both types of antibiotics bind to the 30S subunit of ribosomes to interfere with protein synthesis.

Key Areas Covered

1. What are Aminoglycosides
   • Definition, Characteristics, Importance
2. What are Tetracyclines
   • Definition, Characteristics, Importance
3. Similarities Between Aminoglycosides and Tetracyclines
   • Outline of Common Features
4. Difference Between Aminoglycosides and Tetracyclines
   • Comparison of Key Differences

Key Terms

Aminoglycosides, Tetracyclines

What are Aminoglycosides

Aminoglycosides are semisynthetic antibiotics that inhibit the protein synthesis of bacteria. They are widely used against Gram-negative enteric bacteria in bacteremia and sepsis. Streptomycin, kanamycin, amikacin, tobramycin, gentamycin, and neomycin are some examples of aminoglycosides.

Figure 1: Streptomycin

When considering the mechanism of action, aminoglycosides bind to the 30S ribosomal subunit to interfere with protein synthesis. However, they interfere with the peptide formation and involve in the misreading of mRNA and breakup of polysomes. On the other hand, the action of aminoglycosides is bactericidal and kills bacteria in the body. In addition, their action is prolonged.

What is a Tetracyclines

Tetracyclines are broad-spectrum antibiotics that can act against both Gram-positive and Gram-negative bacteria. The action of tetracyclines is bacteriostatic, inhibiting the reproduction of bacteria. However, apart from bacteria, tetracyclines act against chlamydiota, mycoplasmatota, rickettsiae, and protozoan parasites. Some examples of tetracyclines include tetracycline, oxytetracycline, demeclocycline, lymecycline, doxycycline, etc. However, all tetracyclines share the same four hydrocarbon-ring structures.

Figure 2: Tetracyclines

Furthermore, same as aminoglycosides, tetracyclines inhibit the protein synthesis of bacteria. The reversible binding of tetracycline into the 30S unit of ribosomes blocks the binding of aminoacyl-tRNA to the acceptor site. This blocks the peptide chain growth and bacterial protein synthesis is blocked. Therefore, bacteria can no longer maintain proper functioning and will be unable to grow or further replicate. Since tetracyclines are bacteriostatic, they do not kill bacteria but act against multiplying bacteria. Normally, tetracyclines are short-acting and they passively diffuse through porin channels in the bacterial membrane. Apart from the 30S subunit, they also bind to some extent to the bacterial 50S ribosomal subunit and may alter the cytoplasmic membrane, causing intracellular components to leak from bacterial cells.

Similarities Between Aminoglycosides and Tetracyclines

• Aminoglycosides and tetracyclines are two types of bacteriostatic antibiotics that inhibit the protein synthesis of bacteria.
• They bind to the 30S unit of ribosomes to inhibit protein synthesis.

Difference Between Aminoglycosides and Tetracyclines

Definition

Aminoglycosides refer to any of a group of antibiotics (such as streptomycin and neomycin) that inhibit bacterial protein synthesis and are active especially against gram-negative bacteria, while tetracycline refers to any of a large group of antibiotics with a molecular structure containing four rings.

Co-structure

Aminoglycosides have an amino sugar structure while tetracyclines have the same four hydrocarbon-ring structures.

Uptake by Bacteria

Bacteria uptake aminoglycosides through active transport while tetracyclines passively diffuse the bacterial cell.

Action

Usually, aminoglycosides are bactericidal that kill bacteria while tetracyclines are bacteriostatic that stop the reproduction of bacteria.  

Type of Bacteria

Aminoglycosides act against Gram-negative bacteria while tetracyclines act against both Gram-positive and Gram-negative bacteria.  

Examples

Streptomycin, kanamycin, amikacin, tobramycin, gentamycin, and neomycin are some examples of aminoglycosides while the examples of tetracyclines include tetracycline, oxytetracycline, demeclocycline, lymecycline, doxycycline, etc.

Length of the Action

Aminoglycosides have prolonged action while tetracyclines have short-time action.

Conclusion

In brief, aminoglycosides and tetracyclines are two types of antibacterial substances that inhibit the protein synthesis of bacteria. Both antibiotics bind to the 30S unit of the ribosomes and block the binding of amino acids to the ribosome. However, tetracyclines inhibit the growth of bacteria while aminoglycosides kill bacteria. Therefore, the main difference between aminoglycosides and tetracyclines is their action against bacteria.

References:

1. Krause KM, Serio AW, Kane TR, Connolly LE. Aminoglycosides: An Overview. Cold Spring Harb Perspect Med. 2016 Jun 1;6(6):a027029. doi: 10.1101/cshperspect.a027029. PMID: 27252397; PMCID: PMC4888811.
2. Shutter MC, Akhondi H. Tetracycline. [Updated 2022 Jul 4]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2022 Jan-. 

Image Courtesy:

1. “Streptomycin2” By NEUROtiker- Own Work (Public Domain) via Commons Wikimedia
2. “Tetracycline numbering” By Vaccinationist – Own Work (CC BY-SA 4.0) via Commons Wikimedia