Setting epidemiological cut-off values relevant to MIC and disc diffusion data for Aeromonas salmonicida generated by...

Area of Science:

• Veterinary Microbiology
• Antimicrobial Resistance
• Aquatic Animal Health

Background:

• The Clinical and Laboratory Standards Institute (CLSI) previously established epidemiological cut-off values for key antimicrobials against Aeromonas salmonicida.
• These initial values were based on limited laboratory data, necessitating further validation.
• Aeromonas salmonicida is a significant pathogen affecting fish health and aquaculture.

Purpose of the Study:

• To generate and aggregate antimicrobial susceptibility data from additional laboratories for Aeromonas salmonicida.
• To calculate provisional epidemiological cut-off values for florfenicol, oxolinic acid, and oxytetracycline.
• To provide updated susceptibility data for improved diagnostics and treatment strategies in aquaculture.

Main Methods:

• Generation of minimum inhibitory concentration (MIC) and disc diffusion susceptibility data against Aeromonas salmonicida isolates.
• Aggregation of newly generated data with previously published data from multiple laboratories.
• Calculation of provisional epidemiological cut-off values based on aggregated datasets.

Main Results:

• Provisional MIC cut-off values: florfenicol ≤4 µg ml⁻¹, oxolinic acid ≤0.0625 µg ml⁻¹, oxytetracycline ≤1 µg ml⁻¹ (from 4 laboratories).
• Provisional disc diffusion cut-off values: florfenicol ≥30 mm, oxolinic acid ≥32 mm, oxytetracycline ≥25 mm (from 5 laboratories).
• An additional provisional disc diffusion cut-off value for ampicillin (≥29 mm) was determined from 4 laboratories.

Conclusions:

• The aggregated data support the establishment of provisional epidemiological cut-off values for important antimicrobials against Aeromonas salmonicida.
• These provisional values, derived from a broader range of laboratories, enhance the reliability of susceptibility testing.
• The findings contribute to effective antimicrobial stewardship in aquaculture by providing updated reference points for Aeromonas salmonicida resistance monitoring.