The microflora of rainbow trout intestine: a comparison of traditional andmolecular identification

The culturability of the intestinal microflora of 48 rainbow trout was dete cted by comparing direct microscopic counts (4',6-diamidino-2-phenylindole, DAPI) with plate counts (tryptone soya agar, TSA). In general, a high perc entage (average 50%) of the microflora could be cultured. The counts of the intestinal microflora varied 3-5 log units between fish within the same sa mpling point. A total of 504 bacteria were identified by physiologic criter ia and 153 strains also by partial sequencing of the 16S rRNA gene. High ag reement was found between classical and molecular identification. The domin ant intestinal microflora was identified as bacteria belonging to the gamma subclass of Proteobacteria (of the genera Citrobacter, Aeromonas and Pseud omonas), to the Gram-positive bacteria with low G + C-content (of the genus Carnobacterium) and as bacteria belonging to the beta subclass of Proteoba cteria. However, the composition of the intestinal microflora showed high v ariation among three investigated fish farms and also at different time poi nts within one fish farm. (C) 2000 Elsevier Science B.V. All rights reserve d.