Antibiotics Inhibiting DNA Synthesis

Overview

This lecture reviews antibiotics that inhibit microbial DNA synthesis, focusing on fluoroquinolones, with mention of metronidazole and quinolones.

Metronidazole (Flagyl) interferes with microbial DNA replication and can also act as an antiprotozoal agent.
These antibiotics target the ability of microbes to replicate their DNA and RNA.

Quinolones were discovered as a byproduct of synthesizing the antimalarial drug chloroquine.
Nalidixic Acid is the main quinolone to know; it is effective only for urinary tract infections (UTIs).

Chemically modified quinolones are called fluoroquinolones and are widely used antibiotics.
Examples of fluoroquinolones include Ciprofloxacin (Cipro) and Levofloxacin.
Fluoroquinolones inhibit the enzyme DNA gyrase, which bacteria need to prevent DNA from overcoiling during replication.
Human cells use a different enzyme, making fluoroquinolones selectively toxic to bacteria.
Fluoroquinolones are broad-spectrum, effective against both gram-positive and gram-negative bacteria.
Commonly used to treat respiratory, abdominal, skin, and other types of infections.

Metronidazole — An antibiotic and antiprotozoal that inhibits DNA replication in microbes.
Quinolones — A class of antibiotics targeting DNA synthesis; Nalidixic Acid is a notable example.
Nalidixic Acid — A quinolone antibiotic used mainly for urinary tract infections.
Fluoroquinolones — Chemically modified quinolones, broad-spectrum antibiotics (e.g., Ciprofloxacin, Levofloxacin).
DNA Gyrase — Bacterial enzyme required for proper DNA replication; targeted by quinolones and fluoroquinolones.
Selective Toxicity — The ability of a drug to target microbes without harming human host cells.

Review the differences between quinolones and fluoroquinolones.
Memorize key drug examples: Nalidixic Acid, Ciprofloxacin, Levofloxacin.
Understand the mechanism of action and spectrum of activity for these antibiotics.