M42-A

Methods for Antimicrobial Disk Susceptibility Testing of Bacteria Isolated From Aquatic Animals; Approved Guideline

Antimicrobial susceptibility testing is recommended to determine which antimicrobial agents should be considered for treating a bacterial pathogen. Many bacteria that cause disease in aquatic animals require growth conditions that vary substantially from routine terrestrial bacterial pathogens. It has thus become desirable to develop antimicrobial testing standards for organisms that prefer or require conditions such as lower temperatures, semisolid media, or supplemented media (e.g., NaCl, serum).
This guideline describes the standard agar disk diffusion method and quality control criteria for testing Group 1 aquatic bacteria.These organisms can grow readily on standard Mueller-Hinton agar, and are readily cultured at temperatures of 22 + 2 °C and 28 + 2 °C. Quality control ranges for Escherichia coli ATCCr 25922 and Aeromonas salmonicida subsp. salmonicida ATCCr 33658 when tested at 22 °C, 28 °C, and 35 ± 2 °C (E. coli only) are listed for different antimicrobial agents used to varying degrees in global aquaculture.
Future editions of this guideline will incorporate additional data, as they become available. Still needed are methods for testingother groups of aquatic pathogens, such as the gliding bacteria, obligate halophiles, and gram-positive cocci. In addition, interpretive criteria will also need to be developed, which requires a correlation between pharmacokinetic/pharmacodynamic properties of the drug, in vitro susceptibility data, and clinical outcomes.