Antimicrobial susceptibility testing in Sweden. III. Methodology for susceptibility testing

Area of Science:

• Microbiology
• Clinical Laboratory Science

Background:

• Standardization of antibiotic susceptibility testing is crucial for accurate clinical decisions.
• The Swedish Reference Group for Antibiotics, Subcommittee for Methodology (SRGA-M), addressed the need for standardized disk diffusion methods.
• Variability in susceptibility testing can lead to misinterpretation of antibiotic resistance.

Purpose of the Study:

• To standardize the disk diffusion methodology for antibiotic susceptibility testing.
• To establish reliable breakpoints for bacterial isolates based on in vitro data.
• To enhance the epidemiological surveillance of antibiotic resistance.

Main Methods:

• Collected in vitro disk diffusion data from five clinical laboratories.
• Compared data with reference laboratory minimum inhibitory concentrations (MICs) and inhibition zones.
• Utilized histograms of inhibition zones and MICs to determine breakpoints.
• Recommended specific tests for detecting resistance mechanisms like beta-lactamase production and altered penicillin-binding proteins.

Main Results:

• Established distributions of inhibition zones and MICs for clinically relevant bacterial species.
• Successfully integrated reference data into compiled zone histograms for breakpoint decisions.
• Demonstrated the utility of the standardized disk diffusion procedure in detecting extended-spectrum beta-lactamases in enterobacteria.
• Highlighted the value of inhibition zone registration for epidemiological surveillance.

Conclusions:

• The standardized disk diffusion procedure provides a robust method for antibiotic susceptibility testing.
• Established breakpoints facilitate accurate interpretation of resistance.
• This approach significantly aids in the epidemiological surveillance of antibiotic resistance patterns.
• Specific tests are recommended for identifying key resistance mechanisms in various pathogens.