CLSI M49-A

Methods for Broth Dilution 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 susceptibility testing standards for organisms that prefer or require conditions, such as lower temperatures, semisolid media, or supplemented media (e.g., NaCl,serum).
Clinical and Laboratory Standards Institute (CLSI) document M49-A-Methods for Broth Dilution Susceptibility Testing of Bacteria Isolated From Aquatic Animals; Approved Guideline describes a standardized broth dilution method and quality control criteria for testing Group 1 aquatic bacteria. These organisms grow readily in cation-adjusted Mueller-Hinton broth (CAMHB), 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 ten different antimicrobial agents (ampicillin, enrofloxacin, erythromycin, florfenicol, flumequine, gentamicin, ormetoprim-sulfadimethoxine, oxolinic acid, oxytetracycline, and trimethoprim-sulfamethoxazole).
Future editions of this document will incorporate additional data, as they become available. Still needed are methods for testing other groups of aquatic bacterial 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.