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Improved Method for Determining Antibiotic Susceptibility of Flavobacterium columnare Isolates by Broth Microdilution
Author(s) -
Darwish Ahmed M.,
Farmer Bradley D.,
Hawke John P.
Publication year - 2008
Publication title -
journal of aquatic animal health
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.507
H-Index - 52
eISSN - 1548-8667
pISSN - 0899-7659
DOI - 10.1577/h07-047.1
Subject(s) - enrofloxacin , broth microdilution , florfenicol , microbiology and biotechnology , biology , flumequine , oxytetracycline , minimum inhibitory concentration , antibiotics , veterinary medicine , ciprofloxacin , medicine
A simple and reproducible microdilution method was developed to test the susceptibility of the bacterium Flavobacterium columnare to antibiotics in vitro. The testing was conducted at 28°C for 44–48 h at two dilutions of Mueller–Hinton broth (DMHB) using a standardized inoculum, a reference isolate of Escherichia coli ATCC25922 as a quality control organism, positive and negative control wells, and standardized custom‐made microtiter plates. The E. coli ATCC25922 and F. columnare ATCC23463 (the species type strain) had significantly better growth in DMHB at 1:5 (4 g/L) than at 1:7 (3 g/L). The E. coli ATCC25922 was found to be acceptable as a reference isolate and produced minimum inhibitory concentration (MIC) values similar to those in the range published by the Clinical and Laboratory Standards Institute derived using standard Mueller–Hinton broth. The new method was used to determine the MIC of 23 F. columnare isolates (representing the three genotypes of the species) to enrofloxacin, ampicillin, oxytetracycline, erythromycin, florfenicol, flumequine, ormetoprim/sulfadimethoxine, and oxolinic acid.