Abstract
KDM-2 is a medium widely used for isolation of Renibacterium salmoninarum (R.s.), the causative agent of bacterial kidney disease (BKD). KDM-2 still has a problem for colonization of R.s. at low concentration levels. In the present study, we modified KDM by supplementation of the culture-spent medium of R.s. (SMRs) in substitution of FBS. No difference was observed in the growth rate of R.s. at ≥ 103 cells/mL in KDM broth with 1% FBS regardless of SMRs supplementation. Growth rate of R.s. decreased at 101 cells/mL of inoculation into KDM with 1% FBS, but it was recovered by supplementation of ≥ 1% SMRs into the medium. The activity of SMRs supporting bacterial growth was stable to treatment at 60ºC for 30 min and freezing at -20ºC for 7 days. At inoculation of ≤ 300 CFU of R.s., expected colony counts were obtained on the agar plates containing SMRs, while non or less than half of bacteria colonized on the agar plates without SMRs. It was thus considered that the modified KDM by supplementation of SMRs instead of FBS was convenient and inexpensive for isolation of R.s., especially at low concentration levels.
