Interpretive criteria for disk diffusion susceptibility testing of sparfloxacin

Area of Science:

• Microbiology
• Pharmacology
• Clinical Diagnostics

Background:

• Accurate antibiotic susceptibility testing is crucial for guiding treatment decisions.
• Sparfloxacin is a fluoroquinolone antibiotic with activity against various bacterial pathogens.
• Standardized testing criteria are needed for reliable interpretation of sparfloxacin disk diffusion results.

Purpose of the Study:

• To determine and propose interpretive zone size breakpoints for sparfloxacin disk susceptibility tests using NCCLS and ICS/DIN methods.
• To evaluate the efficacy of 5-microgram sparfloxacin disks for routine susceptibility testing.
• To establish regression equations correlating Minimum Inhibitory Concentrations (MICs) with zone diameters for both methods.

Main Methods:

• Testing of 400 bacterial wild-type isolates with 5-microgram sparfloxacin disks.
• Determination of zone diameter breakpoints for resistance (MIC > 1 mg/L) and susceptibility (MIC ≤ 0.5 mg/L).
• Development of regression equations based on MIC and zone size data from 361 organisms.

Main Results:

• Proposed breakpoints: NCCLS ≤18 mm (resistant), ≥23 mm (susceptible); ICS/DIN ≤20 mm (resistant), ≥25 mm (susceptible).
• Sparfloxacin demonstrated 2-4 times greater activity than ciprofloxacin against Gram-positive cocci and similar activity against Gram-negative rods.
• Quality control zone diameter ranges were established for Escherichia coli ATCC 25922 and Staphylococcus aureus ATCC 29213.

Conclusions:

• The proposed criteria provide reliable interpretation for sparfloxacin disk susceptibility testing.
• Sparfloxacin exhibits potent activity, particularly against Gram-positive bacteria.
• The established regression equations allow for breakpoint adjustments based on varying pharmacokinetic parameters.