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Disk diffusion susceptibility testing of Haemophilus influenzae using haemophilus test medium
G V Doern1, J H Jorgensen, C Thornsberry
1Department of Clinical Microbiology, University of Massachusetts Medical Center, Worcester 01655.
Summary
Reproducible susceptibility testing for Haemophilus influenzae is achievable with Haemophilus Test Medium. This study establishes reliable zone diameter criteria for disk diffusion tests against 19 antimicrobial agents.
Area of Science:
- Microbiology
- Clinical Microbiology
- Antimicrobial Resistance
Background:
- Haemophilus influenzae is a significant human pathogen.
- Accurate susceptibility testing is crucial for guiding antimicrobial therapy.
- Standardized methods are needed for reliable interpretation of antimicrobial susceptibility.
Purpose of the Study:
- To evaluate the reproducibility of disk diffusion and broth microdilution methods for Haemophilus influenzae using Haemophilus Test Medium.
- To determine susceptibility testing criteria for Haemophilus influenzae with 19 antimicrobial agents on Haemophilus Test Medium.
- To establish zone diameter interpretive criteria and MIC correlates for disk diffusion testing.
Main Methods:
- A three-center collaborative study involving disk diffusion and broth microdilution.
- Testing of 150 Haemophilus influenzae strains, including resistant isolates.
- Use of a novel medium, Haemophilus Test Medium, for susceptibility testing.
- Regression analysis to correlate zone diameters with Minimum Inhibitory Concentrations (MICs).
Main Results:
- Both disk diffusion and broth microdilution methods demonstrated high reproducibility.
- Inhibitory zone diameters and MICs were determined for 150 Haemophilus influenzae strains.
- Regression analysis successfully defined zone diameter interpretive criteria and MIC correlates for Haemophilus Test Medium.
Conclusions:
- Haemophilus Test Medium provides a reproducible platform for susceptibility testing of Haemophilus influenzae.
- The established interpretive criteria facilitate accurate disk diffusion testing for various antimicrobial agents.
- This study supports the clinical utility of Haemophilus Test Medium for guiding treatment decisions.