Description
Nalidixic acid sodium salt is used to selectively inhibit susceptible Gram-negative bacteria and to study DNA replication and quinolone resistance mechanisms. It is commonly incorporated into culture media to suppress sensitive organisms or to maintain selective pressure in strains carrying quinolone resistance determinants.
The sodium salt form of nalidixic acid enhances aqueous solubility compared to the free acid, enabling more consistent preparation of antibiotic supplemented media.
Mechanism:
Nalidixic acid is a first generation quinolone that inhibits bacterial DNA gyrase and topoisomerase IV, enzymes essential for DNA supercoiling and replication. By stabilizing the DNA enzyme complex after strand cleavage, it prevents re-ligation of DNA strands and blocks replication, ultimately leading to inhibition of cell division in susceptible bacteria.
Key Features and Advantages
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DNA Gyrase Inhibition: Targets bacterial DNA gyrase and topoisomerase IV, interfering with DNA replication and supercoiling in Gram-negative bacteria.
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Selective Activity for Gram-Negative Organisms: Commonly effective against members of the Enterobacteriaceae family, supporting selective culture applications.
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Quinolone Class Mechanism: Provides a mechanistically distinct option from beta lactams and ribosome targeting antibiotics for comparative studies.
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Enhanced Aqueous Solubility: The sodium salt form improves dissolution in water based media relative to nalidixic acid free acid.
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Tool for Resistance Studies: Frequently used in experiments examining mutations in gyrA, gyrB, and related quinolone resistance determinants.
Common Applications and Usage Notes
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Selective Media for Gram-Negative Isolation: Incorporated into agar to suppress susceptible background flora while allowing growth of resistant strains.
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DNA Replication Research: Used to study bacterial DNA topology, supercoiling dynamics, and replication stress responses.
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Quinolone Resistance Analysis: Applied in selection experiments to isolate mutants with altered DNA gyrase or efflux activity.
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Genetic Mapping Experiments: Utilized to generate selective pressure for identifying chromosomal mutations linked to quinolone resistance.
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Comparative Antimicrobial Studies: Enables evaluation of bacterial responses to DNA replication inhibitors versus other antibiotic classes.
Practical Tips
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pH Sensitivity: Nalidixic acid activity can decrease in acidic media. Maintain neutral to slightly alkaline pH in agar or broth to preserve antimicrobial effectiveness.
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UV Sensitivity in Assays: Because quinolones can interact with UV exposure, avoid unnecessary UV irradiation of plates containing nalidixic acid when conducting mutagenesis or selection experiments.
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Strain Specific Spectrum: Nalidixic acid is primarily active against Gram-negative bacteria and has limited activity against Gram-positive organisms. It is not appropriate when Gram-positive suppression is required.
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Storage/Handling: Upon receipt, store this product at room temperature.
