Cytotoxic activity of the bacterial fish pathogen Flavobacterium columnare on fish cells
Flavobacterium columnare is the causative agent of columnaris disease, the second most prevalent disease in channel catfish, and a leading cause of fish mortality worldwide. Early studies examined the morphology of this Gram-negative gliding rod, and the description of possible virulence factors including extracellular proteases, chondroitin AC lyase, and adhesion. Virulence has been a major focus in the study of F. columnare, beginning with descriptions of strain virulence and variability, and testing conditions under which fish are more susceptible to infections. As vaccines began to be developed, the mechanism by which F. columnare causes host cell death has become an increasingly important topic, allowing insight into the behavior of this bacterium. The goal of this thesis was to demonstrate and describe any cytotoxic effects of F. columnare upon Atlantic salmon kidney (ASK) cells, and elucidate the mechanism by which host cell death is caused. Microscopy and cytotoxicity assays determined that both bacterial cells and bacterial culture supernatants are able to induce host cell death. Further, the detection of two markers of apoptosis in ASK cells exposed to F. columnare cells for 2 to 4 h, caspase 3/7 activity and staining with FITC-labeled annexin V, strongly suggests that F. columnare produces an apoptosis-inducing toxin. Additionally, rapid ASK cell death (<2 >h) induced by bacterial cells at high MOI values (>100) and by incubation in the presence of F. columnare culture supernatant suggests that necrosis is also induced. It was also demonstrated that F. columnare cells exhibited β-hemolytic activity against rainbow trout erythrocytes, but not against sheep erythrocytes. Taken together, the data indicate that F. columnare cells are able to kill host cells by a combination of virulence mechanisms including both apoptosis and necrosis.^
Biology, Molecular|Biology, Cell|Biology, Microbiology|Agriculture, Fisheries and Aquaculture
Alla Alexandra Peselis,
"Cytotoxic activity of the bacterial fish pathogen Flavobacterium columnare on fish cells"
Dissertations and Master's Theses (Campus Access).