by Soto, Esteban

Abstract (Summary)
Name: Esteban Soto Date of Degree: August 11, 2007 Institution: Mississippi State University Major Field: Veterinary Medical Sciences Co-Major Professors: Dr. Michael J. Mauel Dr. Mark L. Lawrence Title of Study: GENETIC AND VIRULENCE DIVERSITY OF FLAVOBACTERIUM COLUMNARE Pages in Study: 48 Candidate for Degree of Master in Sciences Flavobacterium columnare is a freshwater fish bacterium responsible for columnaris disease, the second leading cause of mortality in pond raised catfish in the southeastern United States. Pulsed-field gel electrophoresis (PFGE), in which the entire genome can be represented as a distinct pattern of DNA restriction fragments, is a particularly powerful tool in epidemiology and is now regarded as the gold standard for molecular typing of microorganisms. We developed methods for conducting PFGE on F. columnare, and determined its efficacy for characterizing F. columnare strains isolated from different locations in the Southeastern United States. Our data indicates that digestion of F. columnare genomic DNA with Mlu I yields band patterns that are effective for phylogenetic classification of strains. On the basis of PFGE-derived profiles, similarity dendrograms were constructed for more than 30 F. columnare isolates from the Southeast, resulting in two major genetic groups with more than 60% similarity. Virulence diversity was observed in two different immersion challenge experiments conducted with 16 different isolates in channel catfish fingerlings. A direct correlation was found between the PFGE clustered groups and virulence. Challenged fingerlings with PFGE - Group A isolates resulted in average percent mortalities higher than 60%, whereas challenged fish with PFGE-Group B isolates resulted in average percent mortalities of less than 9%. These results suggests that PFGE-Group A isolates are significantly (p < 0.01) more pathogenic to unabraded channel catfish fingerlings than PFGE-Group B isolates. In a second experimental challenge, abrasion and skin mucus removal from channel catfish fingerlings caused them to become more susceptible to infection and disease from Group B isolates by immersion exposure. However, in fish with intact skin, only PFGE group A isolates were able to cause significant mortalities (p < 0.01). In summary, our results suggest that two genetic divisions of F. columnare channel catfish isolates exist, one that contains strains that are ?primary? pathogens of channel catfish (Group A), and another that are ?secondary? or opportunistic pathogens of catfish (Group B).
Bibliographical Information:

Advisor:Alvin camus; Michael Mauel; Patricia Gaunt; Mark Lawrence

School:Mississippi State University

School Location:USA - Mississippi

Source Type:Master's Thesis

Keywords:accountancy school of


Date of Publication:06/28/2007

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