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Title: Phenotypic characterization and genetic diversity of Flavobacterium columnare isolated from red tilapia, Oreochromis sp. in Thailand

item DONG, HA - Chulalongkorn University
item Lafrentz, Benjamin
item PIRARAT, NOPADON - Chulalongkorn University
item RODKHUM, CHANNARONG - Chulalongkorn University

Submitted to: Journal of Fish Diseases
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/26/2014
Publication Date: 9/17/2015
Citation: Dong, T.H., Lafrentz, B.R., Pirarat, N., Rodkhum, C. 2015. Phenotypic characterization and genetic diversity of Flavobacterium columnare isolated from red tilapia, Oreochromis sp. in Thailand. Journal of Fish Diseases. 38:901-913.

Interpretive Summary: Flavobacterium columnare, the causative agent of columnaris disease, is an important fish pathogen that causes substantial economic losses to warm water fish aquaculture worldwide. In Thailand, disease outbreaks in red tilapia often occur and disease signs were similar to columnaris disease. The objective of this study was to isolate and characterize the F. columnare involved in these disease outbreaks. Diseased red tilapia were sampled from different geographic locations in Thailand and forty-four isolates were recovered and identified as F. columnare. Each isolate exhibited similar characteristics (i.e, phenotype), but the isolates exhibited genetic diversity. The research suggested that the F. columnare isolated in this study were unique based on DNA sequences. This was the first detailed characterization of F. columnare from red tilapia in Thailand and results obtained will be used to further understand the role of F. columnare in disease outbreaks.

Technical Abstract: Flavobacterium columnare is the etiologic agent of columnaris disease and severely affects various freshwater aquaculture fish species worldwide. The objectives of this study were to determine the phenotypic characteristics and genetic variability among F. columnare isolates isolated from red tilapia in Thailand. Forty-four F. columnare isolates were recovered from diseased fish in different geographic locations. The isolates exhibited homologous phenotypic characteristics but exhibited genetic diversity. One isolate was assigned to genomovar I and the remainder were assigned to genomovar II indicating the coexistence of these genomovars but predominance of genomovar II. Phylogenetic analysis of the 16S-23S ISR sequences revealed that a subset of the Thai isolates (n=25) contained a smaller ISR (523-537 bp) and formed a unique ISR phylogenetic group. Phylogenetic analysis of the 16S rRNA gene supported the unique cluster of Thai isolates. This is the first description of the phenotypic and molecular characteristics of F. columnare isolated from red tilapia in Thailand as well as five isolates of F. columnare derived from other fish species including Nile tilapia, koi carp and striped catfish.