Setting epidemiological cut-off values for Vibrio harveyi relevant to MIC data generated by a standardised...

Area of Science:

• Aquatic microbiology
• Antimicrobial resistance
• Veterinary medicine

Background:

• Standardized antimicrobial susceptibility testing (AST) interpretation criteria are lacking for aquaculture, hindering prudent antimicrobial use.
• Vibrio harveyi is a significant pathogen in aquaculture, necessitating reliable AST methods.
• Epidemiological cut-off values (ECOFFs) are crucial for distinguishing susceptible wild-type bacterial populations from resistant ones.

Purpose of the Study:

• To determine epidemiological cut-off values (ECOFFs) for various antimicrobial agents against Vibrio harveyi.
• To assess the suitability of generated data for establishing internationally harmonized AST criteria.
• To support the development of guidelines for responsible antimicrobial use in aquaculture.

Main Methods:

• A standard microdilution method was employed using cation-adjusted Mueller Hinton broth and specific incubation conditions (28°C for 24–28 h).
• Data from 109 unique Vibrio harveyi isolates across 4 independent laboratories (120 observations) were analyzed.
• Normalized resistance and ECOFFinder methods were used to calculate ECOFFs.

Main Results:

• ECOFFs were successfully calculated for six antimicrobial agents: enrofloxacin (≤0.5 µg/ml), florfenicol (≤1 µg/ml), oxolinic acid (≤1 µg/ml), oxytetracycline (≤1 µg/ml), gentamicin (≤4 µg/ml), and trimethoprim/sulfamethoxazole (≤0.5/9.5 µg/ml).
• Data for chloramphenicol, meropenem, and sulfamethoxazole were unsuitable for analysis.
• Vibrio harveyi demonstrated innate resistance to ampicillin; provisional ECOFFs were generated for ceftazidime due to lack of quality control strain data.

Conclusions:

• The generated data for six antimicrobial agents are of sufficient quality and quantity to support the establishment of internationally harmonized ECOFFs for Vibrio harveyi.
• These ECOFFs will facilitate accurate interpretation of AST results, promoting prudent antimicrobial stewardship in aquaculture.
• Addressing the lack of harmonized criteria is essential for effective antimicrobial resistance surveillance and management in global aquaculture.