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Unreliability of disc diffusion test for screening for reduced penicillin susceptibility in Neisseria meningitidis
C Block1, Y Davidson, N Keller
1Department of Clinical Microbiology and Infectious Diseases, Hadassah University Hospital, Jerusalem, Israel. block@md2.huji.ac.il
Abstract:
The 2-U penicillin and microgram oxacillin discs proposed for screening meningococci for susceptibility to penicillin were evaluated by using MICs measured by the E test. The discs yielded unacceptably high frequencies of misclassification of susceptibility category and should be abandoned in favor of MIC estimations. An agreed breakpoint for reduced penicillin susceptibility in meningococci is needed for the E test.
Insights
Penicillin and oxacillin discs for screening Neisseria meningitidis are unreliable. Minimum inhibitory concentration (MIC) testing is recommended over disc screening for accurate penicillin susceptibility results.
Area of Science:
- Microbiology
- Clinical Microbiology
- Antimicrobial Susceptibility Testing
Background:
- Neisseria meningitidis (meningococci) are significant bacterial pathogens.
- Accurate antimicrobial susceptibility testing is crucial for effective treatment.
- Penicillin resistance in meningococci necessitates reliable screening methods.
Purpose of the Study:
- To evaluate the accuracy of 2-unit penicillin and microgram oxacillin discs for screening meningococci penicillin susceptibility.
- To compare disc screening results with Minimum Inhibitory Concentration (MIC) estimations.
Main Methods:
- Evaluation of standard penicillin (2-U) and oxacillin (microgram) discs.
- Comparison with MICs determined by the E test method.
- Analysis of susceptibility category misclassification frequencies.
Main Results:
- Disc screening methods demonstrated unacceptably high rates of misclassification.
- Significant discrepancies were observed between disc diffusion and MIC results.
- The current disc methods are deemed unreliable for clinical use.
Conclusions:
- The 2-U penicillin and microgram oxacillin disc screening methods for meningococci should be discontinued.
- Minimum Inhibitory Concentration (MIC) estimations are superior for determining penicillin susceptibility.
- Establishment of an agreed breakpoint for reduced penicillin susceptibility in meningococci for the E test is required.