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Mutations affecting gyrase in Haemophilus influenzae.

J K Setlow, E Cabrera-Juárez, W L Albritton

    Journal of Bacteriology
    |November 1, 1985
    PubMed
    Summary

    Mutations conferring antibiotic resistance to novobiocin and coumermycin in bacteria were studied. Resistance can arise from structural changes in DNA gyrase or altered gene expression, impacting enzyme levels and regulation.

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    Area of Science:

    • Microbiology
    • Molecular Biology
    • Genetics

    Background:

    • Antibiotic resistance is a growing public health concern.
    • DNA gyrase is a crucial enzyme in bacterial DNA replication and a target for antibiotics like novobiocin and coumermycin.
    • Understanding the mechanisms of resistance is key to developing new therapeutic strategies.

    Purpose of the Study:

    • To investigate the genetic basis of resistance to novobiocin and coumermycin in bacterial mutants.
    • To characterize mutations affecting DNA gyrase structure and function.
    • To explore the relationship between gene dosage, regulatory mutations, and antibiotic resistance levels.

    Main Methods:

    • Isolation and characterization of bacterial mutants resistant to novobiocin, coumermycin, nalidixic acid, and oxolinic acid.
    • In vitro assays of DNA gyrase activity in resistant mutants.
    • Complementation studies using plasmids carrying specific mutations in Escherichia coli.
    • Analysis of gene expression and regulation through genetic manipulation.

    Main Results:

    • Mutations conferring resistance were found to alter DNA gyrase structure or affect enzyme levels.
    • One novobiocin-resistant mutant (Novr) exhibited an altered B subunit of DNA gyrase.
    • Other mutations increased active enzyme levels, with some acting in cis (novB1) and others in trans (novC).
    • Low-level resistance was associated with increased gene copies, while high-level resistance required structural changes and regulatory alterations.
    • Genetic mismatch at the novB locus significantly increased recombination rates during transformation.

    Conclusions:

    • Antibiotic resistance to novobiocin and coumermycin can result from both direct structural alterations of DNA gyrase and changes in enzyme production or regulation.
    • The novB1 mutation may affect the promoter region of the gyrase B subunit gene.
    • High-level resistance is a complex trait involving structural mutations and regulatory elements.
    • Genetic locus mismatch influences DNA recombination dynamics during bacterial transformation.

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