Practical aspects of bacterial culture for the diagnosis of bacterial kidney disease (BKD).

A study was made of practical aspects of culture of Renibacterium salrnonjnarum (R.s.) from the kidney of Atlantic salmon Salmo salar. Samples were taken from fish in sea farms affected by outbreaks of bacterial kidney disease (BKD). Only 67% of the samples positive for growth of R.s. on kidney disease medium (KDM2) were positive on selective kidney disease medium (SKDM). Of the samples positive on KDM2, 98 % were identified as positive after 8 wk of incubation a t 15 "C, whereas only 82 "is of the samples positive on SKDlvl were positive at this time Growth of R.s on KDM2 produced more colonies than growth on SKDM No significant differences in isolation frequency were seen betureen culture from anterior and poster~or k ~ d n e y . If 3 or 4 ~nocu la t~ons were made from each fish, the number of R.s.-poslt~ve f ~ s h increased by 44 0/,) in the lightly infected population of thls study. Both storage of the sample material on swabs in 2 different niodifications of Stuart's transport medium for 24 h, and freezing a t -20 "C for 3 to 4 mo, reduced the sensitivity of culture from lightly infected samples.