What is the Difference Between Macrolides and Tetracyclines

The key difference between macrolides and tetracyclines is that the macrolides contain a macrocyclic lactone ring and inhibit bacterial protein synthesis by binding to the 50S ribosomal subunit, while tetracyclines contain four fused rings and inhibit bacterial protein synthesis by binding to the 30S ribosomal subunit.

Macrolides and tetracyclines are two different antibiotics commonly used to treat bacterial infections. Each antibiotic offers characteristic features and mechanisms to combat distinct bacteria attacking the host. These antibiotics prevent the successful attachment of aminoacyl-tRNA molecules to the 30S ribosomal subunit, restricting further protein synthesis and inhibiting bacteria multiplication and expansion. Understanding the distinct features of macrolides and tetracyclines antibiotic classes helps make the correct choice when implementing an effective treatment plan against bacterial infections.

CONTENTS

1. Overview and Key Difference
2. What are Macrolides 
3. What are Tetracyclines
4. Similarities –  Macrolides and Tetracyclines
5. Macrolides vs Tetracyclines in Tabular Form
6. Summary – Macrolides vs Tetracyclines

What are Macrolides?

Macrolides exert antibacterial effects by binding to the 50S ribosomal subunit of bacteria. As a result, they disrupt the translocation process during protein synthesis, preventing the elongation of the growing peptide chain.

This inhibition ultimately results in the inhibition of bacterial growth. In addition to their antibacterial properties, macrolides possess anti-inflammatory and immunomodulatory effects. Therefore, they are helpful in treating certain respiratory infections, such as community-acquired pneumonia, bronchitis, and sinusitis. Macrolides are also used for individuals with allergies to penicillin-based antibiotics.

What are Tetracyclines?

Tetracyclines are a class of broad-spectrum antibiotics named for their chemical structure, which consists of four fused rings. Tetracyclines work by inhibiting bacterial protein synthesis, preventing bacterial growth and reproduction. Several members of the tetracycline class, including tetracycline, doxycycline, minocycline, and oxytetracycline, are effective against many bacteria, including gram-positive and gram-negative bacteria.

Tetracyclines exhibit their antibacterial effect by binding to the 30S ribosomal subunit of bacteria, which prevents the binding of aminoacyl-tRNA molecules to the ribosome. This disrupts bacterial protein synthesis by preventing adding new amino acids to the growing peptide chain during protein synthesis. In addition to their antibacterial properties, tetracyclines are prescribed for treating infections caused by atypical bacteria, such as chlamydia, mycoplasma, and rickettsia. Furthermore, tetracyclines possess anti-inflammatory properties and use to treat acne, rosacea, and certain skin conditions.

What are the Similarities Between Macrolides and Tetracyclines?

• Macrolides and tetracyclines are used to combat gram-positive, gram-negative, and certain atypical bacteria.
• Both antibiotics work by inhibiting protein synthesis in bacteria, preventing their growth and replication.
• The effectiveness of the two antibiotics has been reduced due to the emergence of bacterial resistance against them.
• Both antibiotics are commonly used to treat respiratory tract infections, such as bronchitis, pneumonia, soft tissue, and skin infections.

What is the Difference Between Macrolides and Tetracyclines?

Macrolides and tetracyclines are widely used to treat bacterial infections. However, there is a distinctive difference between macrolides and tetracyclines in terms of their characteristics and mechanisms of action. Macrolides consist of a macrocyclic lactone ring effective against gram-positive bacteria, with a better safety profile. In contrast, tetracyclines have a four-ring structure and are effective against a broader spectrum of bacteria, including gram-positive, gram-negative, and atypical bacteria. Nevertheless, they cause gastrointestinal disturbances, tooth discoloration, and photosensitivity, especially among children. Macrolides are present in high concentrations in tissues due to higher lipid solubility, while tetracyclines have lower lipid solubility and are present in low concentrations in tissues.

The below infographic presents the differences between macrolides and tetracyclines in tabular form for side-by-side comparison.

Summary – Macrolides vs Tetracyclines

Macrolides and tetracyclines are antibiotics commonly used to treat a broad spectrum of bacterial infections. Macrolides, such as azithromycin and erythromycin, interact with the 50S ribosomal subunit and prevent bacteria from synthesizing proteins due to their macrocyclic lactone ring structure. In contrast, tetracyclines such as doxycycline and minocycline have a four-ring structure and bind to the 30S ribosomal subunit. Other differences include their range of activity, resistance patterns, therapeutic indications, adverse effects, and lipid solubility. Tetracyclines have a broader spectrum and can target some gram-negative and atypical bacteria, but macrolides are more efficient against gram-positive bacteria. Tetracyclines cause gastrointestinal problems and tooth discoloration than macrolides, which have superior safety records. Tetracyclines also have poorer lipid solubility than macrolides, which prevents them from reaching greater tissue concentrations. Understanding the difference between macrolides and tetracyclines makes selecting the appropriate antibiotic treatment for bacterial infections easier.

Reference:

1. Kannan, Krishna, et al. “The General Mode of Translation Inhibition by Macrolide Antibiotics.” Proceedings of the National Academy of Sciences, vol. 111, no. 45, 2014, pp. 15958–15963.
2. Grossman, Trudy H. “Tetracycline Antibiotics and Resistance.” Cold Spring Harbor Perspectives in Medicine, vol. 6, no. 4, 2016.

Image Courtesy:

1. “Tetracycline Structure” (CC0) via Free SVG.