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Effect of incubation temperature and time on the precision of data generated by antibiotic disc diffusion assays
1Department of Microbiology, School of Natural Sciences, National University of Ireland, Galway, Ireland.
Abstract:
The influence on the precision of disc diffusion data of the conditions under which the tests were performed was examined by analysing multilaboratory data sets generated after incubation at 35 °C for 18 h, at 28 °C for 24 h and 22 °C for 24 h and 48 h. Analyses of these data sets demonstrated that precision was significantly and progressively decreased as the test temperature was reduced from 35 to 22 °C. Analysis of the data obtained at 22 °C also showed the precision was inversely related to the time of incubation. Temperature and time related decreases in precision were not related to differences in the mean zone sizes of the data sets obtained under these test conditions. Analysis of the zone data obtained at 28 and 22 °C as single laboratory sets demonstrated that reductions of incubation temperature resulted in significant increases in both intralaboratory and interlaboratory variation. Increases in incubation time at 22 °C were, however, associated with statistically significant increases in interlaboratory variation but not with any significant increase in intralaboratory variation. The significance of these observations for the establishment of the acceptable limits of precision of data sets that can be used for the setting of valid epidemiological cut-off values is discussed.
Insights
Lowering incubation temperatures for disc diffusion tests significantly reduces data precision. Extended incubation times further decrease precision, impacting the reliability of epidemiological cut-off values.
Area of Science:
- Microbiology
- Clinical Diagnostics
- Pharmaceutical Sciences
Background:
- Disc diffusion assays are crucial for antimicrobial susceptibility testing.
- Standardized testing conditions are essential for reliable and reproducible results.
- Variations in incubation temperature and time can affect assay performance.
Purpose of the Study:
- To investigate the impact of varying incubation conditions on the precision of disc diffusion test data.
- To determine how temperature and time affect the reproducibility of antimicrobial susceptibility testing.
- To assess the implications for establishing epidemiological cut-off values.
Main Methods:
- Analysis of multilaboratory disc diffusion data sets.
- Incubation at different temperatures (35°C, 28°C, 22°C) and durations (18h, 24h, 48h).
- Statistical analysis of zone sizes, intralaboratory variation, and interlaboratory variation.
Main Results:
- Precision significantly decreased as incubation temperature was lowered from 35°C to 22°C.
- At 22°C, precision was inversely related to incubation time.
- Reduced temperatures increased both intralaboratory and interlaboratory variation; longer incubation at 22°C increased interlaboratory variation.
Conclusions:
- Incubation temperature and time critically influence disc diffusion test precision.
- Current incubation conditions may compromise the reliability of epidemiological cut-off values.
- Optimizing incubation parameters is necessary for accurate antimicrobial susceptibility testing.
