Interpretive standards for disk susceptibility tests with Sch 21420 and amikacin

Area of Science:

• Microbiology
• Antimicrobial Susceptibility Testing
• Clinical Laboratory Science

Background:

• Aminoglycosides like amikacin and Sch 21420 are crucial antibiotics.
• Accurate disk susceptibility testing (DST) is essential for guiding antimicrobial therapy.
• Evaluating DST methods for related compounds ensures efficient laboratory practices.

Purpose of the Study:

• To evaluate the efficacy of disk susceptibility tests for amikacin and Sch 21420.
• To determine optimal disk concentrations and interpretive zone standards for both agents.
• To assess the applicability of the 'class concept' in DST for these related aminoglycosides.

Main Methods:

• Disk susceptibility tests were performed using various concentrations of amikacin (10, 30 µg) and Sch 21420 (10, 20, 30 µg) disks.
• Interpretive zone standards were established based on minimal inhibitory concentration (MIC) breakpoints.
• Correlation between amikacin and Sch 21420 disk test results was analyzed.

Main Results:

• 30-microgram disks for both amikacin and Sch 21420 are recommended for DST.
• Specific zone standards were proposed for classifying susceptibility and resistance to Sch 21420.
• Amikacin 30-µg disk tests demonstrated high accuracy in predicting susceptibility/resistance to Sch 21420.

Conclusions:

• The 30-µg disk is the preferred concentration for both amikacin and Sch 21420 DST.
• The 'class concept' is applicable, suggesting routine Sch 21420 DST may not be necessary if amikacin DST is performed.
• Standardized DST methods ensure reliable interpretation of antimicrobial susceptibility for effective patient treatment.