Virulence assay of rhizoid and non‐rhizoid morphotypes of Flavobacterium columnare in red tilapia,Oreochromis sp., fry |
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| Authors: | H T Dong S Senapin B LaFrentz C Rodkhum |
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| Affiliation: | 1. Department of Veterinary Microbiology, Faculty of Veterinary Science, Chulalongkorn University, Bangkok, Thailand;2. National Center for Genetic Engineering and Biotechnology, National Science and Technology Development Agency, Pathumthani, Thailand;3. Center of Excellence for Shrimp Molecular Biology and Biotechnology, Mahidol University, Bangkok, Thailand;4. Aquatic Animal Health Research Unit, United States Department of Agriculture‐Agricultural Research Service, Auburn, AL, USA |
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| 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. |
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| Keywords: | colony morphotypes
Flavobacterium columnare
tilapia virulence |
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