Location: Aquatic Animal Health ResearchTitle: Flavobacterium columnare isolated from red tilapia (Oreochromis sp.): emphasis on genetic characterization and virulence of rhizoid and non-rhizoid morphotypes
|DONG, HA THANH - Chulalongkorn University|
|SENAPIN, SAENGCHAN - Mahidol University|
|PIRARAT, NOPADON - Chulalongkorn University|
|RODKHUM, CHANNARONG - Chulalongkorn University|
Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: 9/15/2015
Publication Date: 10/27/2015
Citation: Dong, H., Senapin, S., Lafrentz, B.R., Pirarat, N., Rodkhum, C. 2015. Flavobacterium columnare isolated from red tilapia (Oreochromis sp.): emphasis on genetic characterization and virulence of rhizoid and non-rhizoid morphotypes [abstract]. Flavobacterium 2015. p. 33.
Technical Abstract: Flavobacterium columnare is the causative agent of columnaris disease and severely affects various freshwater fish species worldwide. Here, we described the phenotypic and genetic characterization of F. columnare isolates isolated from farmed red tilapia in Thailand. Additionally, the virulence as well as ability of two morphotypes (rhizoid and non-rhizoid colonies) to adhere to and persist in red tilapia fry was determined. Forty-four F. columnare isolates, which were recovered from diseased fish in different geographic locations, showed homologous phenotypic characteristics but exhibited genetic diversity. 16S-RFLP result indicated the coexistence of two genomovars but a 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. Virulence assay revealed that the typical rhizoid isolate (CUVET1214) was highly virulent whereas the non-rhizoid isolate (CUVET1201) was avirulent to red tilapia fry. Both morphotypes adhered to and persisted in red tilapia fry similarly at 0.5 and 6 h post challenge as determined by whole fish bacterial loads. Tilapia fry challenged with the rhizoid morphotype, however, exhibited significantly higher bacterial loads than the non-rhizoid morphotype at 24 and 48 h post challenge. The results suggested that an inability of the non-rhizoid morphotype to persist in tilapia fry may explain lack of virulence.