Submitted to: Molecular and Cellular Probes
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: April 11, 2005
Publication Date: June 24, 2005
Citation: Darwish, A.M., Ismaiel, A.A. 2005. Genetic diversity of flavobacterium columnare examined by restriction fragment length polymorphism and sequencing of the 16s ribosomal RNA gene and the 16s-23s RDNA spacer. Molecular and Cellular Probes. 19:267-274. Interpretive Summary: Columnaris disease exists worldwide and is considered one of the most serious pathogens to channel catfish, golden shiners, striped bass, largemouth bass and sunfishes. It is the second costly disease to the channel catfish industry in the United States after enteric septicemia of channel catfish. The disease is caused by Flavobacterium columnare. In 2004, as critical step toward controlling this disease, our laboratory developed a definitive identification method of F. columnare using polymerase chain reaction. In the present study, a methodology using the 16S rDNA and the 16S-23S DNA spacer was developed to differentiate and compare the strains of the bacterium implicated in the disease outbreaks in various locations in the world. It was shown that F. columnare strains plaguing the American industry are of three genotypes and those genotypes were compared to the genotypes found in other countries. This knowledge will be indispensable in epidemiology studies tracking the movement of pathogens across international boarders and in protecting the nation against the introduction of any new genotypes of this costly bacterium.
Technical Abstract: Genetic variability among strains of Flavobacterium columnare, isolated in the United States, was characterized by restriction fragment length polymorphism (RFLP) and phylogenetic analysis based on the sequence of the 16S rRNA gene. Twenty-seven isolates of F. columnare were differentiated into three genotypes. The isolates within the genotypes were further grouped based on RFLP of the 16S-23S rDNA spacer. The first genotype had five strains that were further divided into group A (4 strains) and B (1 strain) while the second genotype had 10 strains that were also further divided into group A (4 strains) and B (6 stains). The third genotype had 12 isolates with no differences in the RFLP patterns of the 16S-23S rDNA spacers. The 16S rRNA gene sequences representing the three identified genotypes were compared to the different published sequences by phylogenetic analysis and the results showed the American genotypes 1, 2 and 3 corresponding to genomovar 1, 2, and 3, respectively, reported by Triyanto and Wakabayashi (1999). The study demonstrates a method for RFLP and sequencing of the 16S rRNA gene and the 16-23S rDNA spacer as a useful tool that can be employed in epidemiological studies of F. columnare.