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Evaluation of direct disc diffusion susceptibility testing for bacteriuria using diluted urine against standard CDS
1Division of Microbiology, Southpath, St George Hospital, Kogarah, NSW.
Pathology
|April 1, 1994
Summary
Direct disc diffusion susceptibility testing on urine isolates showed high concordance (98.5%) with the Calibrated Dichotomous Sensitivity (CDS) test. This method is suitable for routine clinical use in identifying Gram-negative bacterial infections.
Area of Science:
- Clinical Microbiology
- Infectious Diseases
- Antimicrobial Susceptibility Testing
Background:
- Urinary tract infections (UTIs) are common, necessitating accurate and efficient antimicrobial susceptibility testing (AST).
- Direct methods for AST can potentially reduce turnaround times compared to traditional culture-based methods.
Purpose of the Study:
- To evaluate the concordance of a direct disc diffusion susceptibility test with the standard Calibrated Dichotomous Sensitivity (CDS) test for Gram-negative organisms in urine specimens.
- To assess the clinical utility of a direct AST method for routine laboratory use.
Main Methods:
- Urine specimens with >= 10(9) organisms/L by microscopy were analyzed.
- Direct disc diffusion and standard Calibrated Dichotomous Sensitivity (CDS) tests were performed on Gram-negative isolates.
- Exclusion criteria included >2 isolates or growth <10(8) CFU/L.
Main Results:
- A total of 361 urines were evaluated, with 2272 organism/antimicrobial test comparisons.
- High concordance of 98.5% was achieved between the direct disc diffusion and CDS methods.
- Common Gram-negative organisms included Escherichia coli, Klebsiella, and Proteus.
Conclusions:
- The direct disc diffusion susceptibility test demonstrates high accuracy and concordance with the standard CDS test.
- This direct method is considered acceptable for routine clinical use in AST for Gram-negative urinary pathogens.