Location: Warmwater Aquaculture Research UnitTitle: Methods for broth dilution susceptibility testing of bacteria isolated from aquatic animals; approved guideline-second edition Author
Submitted to: Book Chapter
Publication Type: Book / Chapter
Publication Acceptance Date: 6/25/2014
Publication Date: 9/25/2014
Citation: Miller, R., Carson, J., Dalsgaard, I., Gaunt, P.S., Gieseker, C., Hawke, J., Reimschuessel, R., Smith, P., Somsiri, T., Wu, C. 2014. Methods for broth dilution susceptibility testing of bacteria isolated from aquatic animals; approved guideline-second edition. Book Chapter. P. 56. Interpretive Summary: This document provides the most up-to-date techniques for the determination of minimal inhibitory concentrations of aquatic bacteria by broth micro- and macrodilution, and criteria for data interpretation and quality control testing.
Technical Abstract: 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 pathogens. It has thus become desirable to develop antimicrobial susceptibility testing standards for organisms that prefer or require certain conditions such as higher temperature, semisolid media, or supplemental media (eg. Blood) Clinical and Laboratory Standards Institute (CLSI) document VET04-A2 Methods for Broth Dilution Susceptibility Testing of Bacteria isolated from Aquatic Animals, Approved Guideline – Second Edition describes two standardized broth dilution methods and QC criteria for testing Groups 1 and 3 aquatic bacteria. Group 1 nonfastidious bacteria grow readily in cation adjusted Mueller-Hinton broth (CAMHB) and are readily cultured at temperatures of 22oC + 2oC and 28oC + 2oC. Group 3 gliding bacteria grow in diluted CAMHB and are readily cultured at temperatures of 18oC or 28oC depending on species. QC ranges for Escherichia coli ATCC® 25922 and Aeromonas salmonicida subsp. salmonicida ATCC® 33658 when tested at 18oC, 22oC or 28oC and 35oC + 2oC (E. coli only) are listed for different antimicrobial agents important to global aquaculture In this revision, two new tables, provided in the corresponding supplement VET03/VET04-S2, contain the first consensus approved interpretive criteria clinical breakpoints (susceptible, intermediate and resistant) and epidemiological cutoff values(wild-type cutoffs) for A. salmonicida isolates. Still needed are the methods for testing and interpreting results for other groups of aquatic bacterial pathogens such as gram-positive cocci, as well as emerging pathogens, like Fransicella spp. Additional interpretive criteria need to be develop which would require correlation between pharmacokinetic-pharmacodynamics properties of the drug, in vitro susceptibility data, and reported clinical outcomes.