Epidemiological cut-off values for Flavobacterium psychrophilum MIC data generated by a standard test protocol

Area of Science:

• Veterinary Microbiology
• Antimicrobial Resistance
• Aquatic Animal Health

Background:

• Flavobacterium psychrophilum is a significant fish pathogen.
• Standardized interpretation of antibiotic susceptibility testing is crucial for effective treatment.
• Epidemiological cut-off values (ECOFFs) help distinguish susceptible wild-type strains from resistant ones.

Purpose of the Study:

• To determine epidemiological cut-off values for common antibiotics against Flavobacterium psychrophilum.
• To provide a standardized method for interpreting antibiotic susceptibility data for this pathogen.

Main Methods:

• MIC values for ten antibiotics against F. psychrophilum were determined in two laboratories.
• The normalized resistance interpretation method was used to calculate ECOFFs.
• Data quality and distribution were assessed to validate ECOFFs.

Main Results:

• Valid ECOFFs were established for erythromycin (≤16 mg L⁻¹), florfenicol (≤2 mg L⁻¹), oxolinic acid (≤0.025 mg L⁻¹), oxytetracycline (≤0.125 mg L⁻¹), and trimethoprim/sulphamethoxazole (≤20 (1/19) mg L⁻¹).
• ECOFFs could not be determined for ampicillin, amoxicillin, ormetoprim/sulphadimethoxine, flumequine, and enrofloxacin due to data limitations.
• Oxolinic acid was proposed as a representative for quinolone susceptibility testing.

Conclusions:

• Established ECOFFs provide a basis for interpreting F. psychrophilum antibiotic susceptibility.
• Further investigation is needed for antibiotics where ECOFFs could not be determined.
• Standardized interpretation aids in antimicrobial stewardship in aquaculture.