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Evaluation of the Etest for penicillin susceptibility testing of Neisseria meningitidis
P Gomez-Herruz1, R González-Palacios, J Romanyk
1Department of Microbiology, Asturias University Hospital, Madrid, Spain.
Abstract:
Susceptibility to penicillin of 30 strains (one isolate per patient) of Neisseria meningitidis isolated from blood (N = 19) or cerebrospinal fluid (N = 11) was studied by two methods. Minimum inhibitory concentrations (MICs) obtained with the Etest were compared to those obtained by the National Committee for Clinical Laboratory Standards agar dilution method. Twenty meningococci (67%) relatively resistant to penicillin were identified by both methods. The mean MIC from the reference method was 0.32 micrograms/ml (range, 0.2-1) and by the Etest method was 0.35 micrograms/ml (range, 0.19-1.25). All MICs obtained by the Etest method were within one dilution of the MICs obtained by the reference method. Because of the increase in penicillin MIC of meningococcal isolates in Spain, we evaluated the performance of the Etest as an alternative method for penicillin-susceptibility testing of N. meningitidis. The Etest is a simple and accurate method for determining the susceptibility of N. meningitidis to penicillin.
Insights
Penicillin resistance in Neisseria meningitidis is increasing. The Etest method accurately identifies penicillin-resistant meningococci (Neisseria meningitidis), offering a reliable alternative for susceptibility testing.
Area of Science:
- Microbiology
- Clinical Laboratory Science
- Infectious Diseases
Background:
- Increasing penicillin resistance in Neisseria meningitidis poses a public health concern.
- Accurate susceptibility testing is crucial for effective treatment of meningococcal infections.
Purpose of the Study:
- To evaluate the performance of the Etest as an alternative method for penicillin-susceptibility testing of Neisseria meningitidis.
- To compare Etest results with a standard agar dilution method.
Main Methods:
- Susceptibility testing of 30 Neisseria meningitidis isolates using both Etest and National Committee for Clinical Laboratory Standards agar dilution methods.
- Determination of Minimum Inhibitory Concentrations (MICs) for penicillin.
Main Results:
- Sixty-seven percent (20/30) of isolates showed relative resistance to penicillin by both methods.
- Mean MICs were comparable: 0.32 µg/mL (reference) vs. 0.35 µg/mL (Etest).
- Etest MICs consistently fell within one dilution of the reference method.
Conclusions:
- The Etest is a simple, accurate, and reliable method for penicillin-susceptibility testing of Neisseria meningitidis.
- Etest performance is comparable to the standard agar dilution method for this application.
- This method can aid in monitoring and managing penicillin resistance in meningococcal isolates.