Question

Which of the following antimicrobials inhibits the activity of DNA gyrase? a. polymyxin B b. clindamycin c. nalidixic acid d. rifampin

Short answer

The antimicrobial that inhibits the activity of DNA gyrase is nalidixic acid, option c.

Step-by-step solution

Understand the function of DNA gyrase

DNA gyrase is an enzyme that introduces supercoiling into DNA. It is essential for the process of replication in bacteria. Some antimicrobials target this enzyme to inhibit bacterial growth.

Identify antimicrobials and their mechanisms

Review the mechanisms of action of the listed antimicrobials. Polymyxin B disrupts cell membranes, clindamycin interferes with protein synthesis, nalidixic acid inhibits DNA gyrase, and rifampin inhibits RNA polymerase.

Select the correct antimicrobial

Among the options given, nalidixic acid is the antimicrobial known to inhibit the activity of DNA gyrase. Therefore, the correct choice is c. nalidixic acid.

Key concepts

Nalidixic Acid

Nalidixic acid plays a critical role in the world of antibiotics as a DNA gyrase inhibitor. Discovered in the 1960s, it marked the beginning of the era of synthetic antibacterials. It's part of a larger group of antibiotics known as quinolones, which act against a broad spectrum of bacteria.

Nalidixic acid specifically targets and binds to the bacterial DNA gyrase, a crucial enzyme required for DNA replication and supercoiling. By interfering with this enzyme, nalidixic acid effectively halts bacterial DNA replication, thereby stopping the growth of bacteria. It is particularly effective against Gram-negative bacteria and is commonly used to treat urinary tract infections. While useful, nalidixic acid is usually reserved for specific bacterial infections because its overuse has led to the development of resistance among some bacterial strains.

Antimicrobial Mechanisms

Understanding antimicrobial mechanisms is vital in developing strategies to fight bacterial infections. Antimicrobials work by targeting specific parts of the bacterial cell which are crucial for their survival and reproduction. These targets include the bacterial cell wall, DNA replication enzymes such as DNA gyrase, and protein synthesis.

• Cell wall synthesis inhibitors, like penicillins, prevent the formation of the cell wall, leading to bacterial lysis.
• DNA replication inhibitors, such as nalidixic acid, bind to DNA gyrase, causing DNA breakage and inhibiting bacterial multiplication.
• Protein synthesis inhibitors, for example tetracyclines, bind to the bacterial ribosome and prevent the translation of RNA into functional proteins.

Each antimicrobial agent has a unique mechanism of action, which is why a deep understanding of these mechanisms helps healthcare professionals to prescribe the most effective treatment for bacterial infections.

Bacterial DNA Replication

Bacterial DNA replication is a highly coordinated process that is essential for the survival and proliferation of bacteria. It involves unwinding the DNA double helix, synthesizing a new strand complementary to the existing template, and then repackaging the DNA into a suitable structure for segregation into daughter cells.

The enzyme DNA gyrase is a 'topoisomerase', which means it controls the topology of DNA. During replication, DNA gyrase introduces negative supercoils, effectively untwisting the DNA double helix and making it easier for other enzymes to replicate the genetic material. Inhibitors of DNA gyrase, such as nalidixic acid, exert their antibacterial effects precisely because they obstruct this essential step in DNA replication, leading to the build-up of supercoils and eventual cessation of bacterial cell division.