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[Influence of antibiotic disk charge on concordance curve of cefotaxime ]
Abstract:
The activity of new cephalosporins is considerably higher than that of the first molecules. However antibiotic desk charge used for the agar diffusion method is still 30 micrograms. The disk diffusion - MIC distribution is not linear. The authors observed the influence of disk charge on the aspect of this distribution in order to determine the change permitting the best linearity. One hundred sixty five strains were studied using the agar diffusion and dilution methods. Their MICs were distributed from 0.015 to 128 mg/l. The disk charges studied were 5, 10, 15, 20, 25 and 30 micrograms. The results confirmed the parabolic aspect of concordance curve. This phenomenon was observed at higher disk charges (20, 25 and 30 micrograms). The linearity is better with the curves calculated from 5 and 10 micrograms. The correlation coefficients between these two charges were 0.92. However the inhibition diameters in 5 micrograms were too small to permit a clear differentiation between resistant and intermediate strains. The best discrimination is obtained with 10 micrograms. The zone diameter breakpoints were greater than or equal to 18 mm for susceptible 12 to 17 mm for intermediate, and less than or equal to 11 mm for resistant.
Insights
Optimizing antibiotic disk diffusion assays is crucial for accurate susceptibility testing. Lowering antibiotic disk charges to 10 micrograms improves linearity and discrimination between resistant and susceptible bacterial strains.
Area of Science:
- Microbiology
- Clinical Pharmacy
- Antibiotic Resistance
Context:
- Newer cephalosporins exhibit enhanced antimicrobial activity compared to earlier generations.
- Standard antibiotic disk charges for agar diffusion assays remain at 30 micrograms.
- The relationship between disk diffusion and minimum inhibitory concentration (MIC) is non-linear.
Purpose:
- To investigate the influence of varying antibiotic disk charges on the linearity of disk diffusion-MIC distribution.
- To determine the optimal disk charge for improved accuracy in bacterial susceptibility testing.
- To enhance the discriminatory power of the agar diffusion method for antibiotic resistance.
Summary:
- One hundred sixty-five bacterial strains were tested using agar diffusion and dilution methods with disk charges ranging from 5 to 30 micrograms.
- Higher disk charges (20-30 micrograms) resulted in a parabolic concordance curve, indicating poor linearity.
- Lower disk charges (5 and 10 micrograms) demonstrated better linearity, with 10 micrograms providing the best discrimination between susceptible, intermediate, and resistant strains.
Impact:
- The study identifies 10 microgram as the optimal disk charge for improved linearity and discrimination in cephalosporin susceptibility testing.
- Findings suggest a revision of current disk diffusion protocols to enhance accuracy in clinical settings.
- Improved accuracy in susceptibility testing can lead to more effective antibiotic stewardship and better patient outcomes.