title: Virulence assay of rhizoid and non-rhizoid morphotypes of Flavobacterium columnare in red tilapia, Oreochromis sp., fry.
abstract: Numerous isolates of Flavobacterium columnare were previously recovered from red tilapia, Oreochromis sp., exhibiting columnaris-like disease in Thai farms, and the phenotypic and genetic characteristics were described. The objective of this study was to determine the virulence of two morphotypes (rhizoid and non-rhizoid colonies) of F. columnare and to determine their ability to adhere to and persist in red tilapia fry. The results showed that the typical rhizoid isolate (CUVET1214) was a highly virulent isolate and caused 100% mortality within 24 h following bath challenge of red tilapia with three different doses. The non-rhizoid isolate (CUVET1201) was avirulent to red tilapia fry. Both morphotypes adhered to and persisted in tilapia similarly at 0.5 and 6 h post-challenge as determined by whole fish bacterial loads. At 24 and 48 h post-challenge, fry challenged with the rhizoid morphotype exhibited significantly higher bacterial loads than the non-rhizoid morphotype. The results suggested that an inability of the non-rhizoid morphotype to persist in tilapia fry may explain lack of virulence.
authors.affiliation: Department of Veterinary Microbiology, Faculty of Veterinary Science, Chulalongkorn University, Bangkok, Thailand.
authors.forename: H T
authors.initials: HT
authors.lastname: Dong
authors.affiliation: National Center for Genetic Engineering and Biotechnology, National Science and Technology Development Agency, Pathumthani, Thailand.|Center of Excellence for Shrimp Molecular Biology and Biotechnology, Mahidol University, Bangkok, Thailand.
authors.forename: S
authors.initials: S
authors.lastname: Senapin
authors.affiliation: Aquatic Animal Health Research Unit, United States Department of Agriculture-Agricultural Research Service, Auburn, AL, USA.
authors.forename: B
authors.initials: B
authors.lastname: LaFrentz
authors.affiliation: Department of Veterinary Microbiology, Faculty of Veterinary Science, Chulalongkorn University, Bangkok, Thailand.
authors.forename: C
authors.initials: C
authors.lastname: Rodkhum
mesh_terms: D000818:Animals; D023681:Cichlids; D005393:Fish Diseases / Q000382:microbiology*; D045826:Flavobacteriaceae Infections / Q000382:microbiology / Q000662:veterinary*; D005417:Flavobacterium / Q000472:pathogenicity* / Q000502:physiology*; D014774:Virulence
keywords: Flavobacterium columnare; colony morphotypes; tilapia; virulence