Bacteriophage Resistance Affects Flavobacterium columnare Virulence Partly via Mutations in Genes Related to Gliding Motility and the Type IX Secretion System
Heidi M. T. Kunttu, Anniina Runtuvuori‐Salmela, Krister Sundell, Tom Wiklund, Mathias Middelboe, Lotta Landor, Roghaieh Ashrafi, Ville Hoikkala, Lotta‐Riina Sundberg
Abstract
Phage resistance of infectious bacteria is a common phenomenon posing challenges for the development of phage therapy. Along with a growing world population and the need for increased food production, constantly intensifying animal farming has to face increasing problems of infectious diseases. Columnaris disease, caused by Flavobacterium columnare, is a worldwide threat for salmonid fry and juvenile farming. Without antibiotic treatments, infections can lead to 100% mortality in a fish stock. Phage therapy of columnaris disease would reduce the development of antibiotic-resistant bacteria and antibiotic loads by the aquaculture industry, but phage-resistant bacterial isolates may become a risk. However, phenotypic and genetic characterization of phage-resistant F. columnare isolates in this study revealed that they are less virulent than phage-susceptible isolates and thus not a challenge for phage therapy against columnaris disease. This is valuable information for the fish farming industry globally when considering phage-based prevention and curing methods for F. columnare infections.