Epidemiological cut-off values for Vibrio anguillarum MIC and disc diffusion data generated by standardised methods.

Area of Science:

• Veterinary Microbiology
• Antimicrobial Resistance
• Aquatic Animal Health

Background:

• Vibrio anguillarum is a significant pathogen in aquaculture.
• Standardized antimicrobial susceptibility testing is crucial for effective treatment and resistance monitoring.
• Epidemiological cut-off values (ECOFFs) are essential for distinguishing wild-type from non-wild-type (resistant) strains.

Purpose of the Study:

• To generate data for establishing epidemiological cut-off values for minimum inhibitory concentration (MIC) and disc-diffusion zone diameters for Vibrio anguillarum.
• To standardize antimicrobial susceptibility testing (AST) methods for this important fish pathogen.

Main Methods:

• Testing of 261 unique Vibrio anguillarum isolates using standard microbiological methods.
• Multi-laboratory determination of MICs for 11 antimicrobial agents and disc diffusion zones for 10 agents.
• Application of statistical methods to calculate ECOFFs, with quality control (QC) data used for validation.

Main Results:

• ECOFFs were successfully calculated for MIC data (florfenicol, gentamicin, oxytetracycline, trimethoprim/sulfamethoxazole) and disc zone data (enrofloxacin, florfenicol, gentamicin, oxolinic acid, oxytetracycline, trimethoprim/sulfamethoxazole).
• Provisional ECOFFs were determined for meropenem and ceftazidime due to lack of QC data.
• Some agent-isolate combinations did not meet statistical requirements for ECOFF determination.

Conclusions:

• The generated data provide a basis for setting international consensus ECOFFs for Vibrio anguillarum AST.
• Validated ECOFFs will improve the accuracy of antimicrobial susceptibility testing and resistance surveillance in aquaculture.
• Further data are needed for certain antimicrobial agents to establish robust ECOFFs.