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[The correlation between the MICs deduced from Showa disk method and the MICs determined by micro-dilution method]
S Moroizumi1, F Kasitani, M Isikawa
1Department of Clinical Laboratory, Omori Hospital, Toho University, Tokyo.
Rinsho Byori. the Japanese Journal of Clinical Pathology
|October 1, 1994
Summary
The Showa disk method offers a simpler way to determine bacterial drug susceptibility, potentially replacing breakpoints with Minimum Inhibitory Concentration (MIC) estimations. This study validated its accuracy against broth micro-dilution, showing good agreement for routine clinical use in Japan.
Area of Science:
- Clinical Microbiology
- Antimicrobial Susceptibility Testing
- Bacterial Infections
Context:
- The disc diffusion technique, including the Kirby-Bauer (KB) method, is a standard for bacterial drug susceptibility testing due to its simplicity and cost-effectiveness.
- Clinical laboratories rely on breakpoints to categorize bacterial susceptibility, but variations in pharmacokinetics and the lack of established breakpoints in Japan necessitate alternative methods.
- Minimum Inhibitory Concentration (MIC) reporting may be more informative than breakpoint categorization given these limitations.
Purpose:
- To evaluate the Showa disk method, which deduces MIC from zone diameter using linear regression, as a valuable tool for routine drug susceptibility testing in Japan.
- To compare MICs deduced by the Showa disk method with those determined by broth micro-dilution, addressing the shift from agar dilution to micro-dilution methods.
- To assess the agreement and correlation between the two methods using a diverse set of bacterial strains and antimicrobial agents.
Summary:
- The study compared MICs derived from the Showa disk method with broth micro-dilution results for 110 gram-positive and gram-negative bacteria across 7 antimicrobial agents.
- A total agreement of 77% within a 1-log2 dilution difference and a correlation coefficient of 0.929 were achieved, indicating a strong relationship between the methods.
- Minor discrepancies were noted for specific antibiotic-non-susceptible bacterial combinations, including tetracycline and ofloxacin against H. influenzae, and ceftizoxime against E. coli and K. pneumoniae.
Impact:
- The Showa disk method demonstrates good correlation with broth micro-dilution, suggesting its potential as a reliable and valuable alternative for routine MIC determination in Japanese clinical laboratories.
- This method could improve the accuracy and clinical relevance of susceptibility reporting, aiding in effective antimicrobial therapy selection.
- Further validation may refine its application for specific bacterial-antimicrobial combinations.