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High concentration of ampicillin and the Eagle effect among gram-negative rods

K Goldstein, V T Rosdahl

    Chemotherapy
    |January 1, 1981
    PubMed

    Insights

    Most Escherichia coli strains exhibit the paradoxical zone phenomenon with ampicillin. However, the observed Eagle effect has minimal clinical significance for treating E. coli infections with high-dose ampicillin.

    Area of Science:

    • Microbiology
    • Bacteriology
    • Clinical Pharmacology

    Background:

    • The paradoxical zone phenomenon is an antimicrobial resistance pattern.
    • Escherichia coli is a common bacterial pathogen.
    • Ampicillin is a widely used antibiotic.

    Purpose of the Study:

    • To investigate the prevalence of the paradoxical zone phenomenon in Escherichia coli strains.
    • To determine the occurrence and clinical relevance of the Eagle effect in ampicillin-treated E. coli.

    Main Methods:

    • Triple layer technique used to detect the paradoxical zone phenomenon around ampicillin discs.
    • Quantitative analysis of bacterial growth with varying ampicillin concentrations for selected strains.

    Main Results:

    • 76 out of 79 (96.2%) Escherichia coli strains showed the paradoxical zone phenomenon.
    • Only 5 of 7 positive strains demonstrated the Eagle effect.
    • All 3 negative strains did not exhibit the Eagle effect.

    Conclusions:

    • The paradoxical zone phenomenon is common in Escherichia coli.
    • The Eagle effect observed in this study is unlikely to be clinically significant for high-dose ampicillin therapy.
    • Further research may be warranted to understand resistance mechanisms.

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