Immunization with bacterial antigens: Flavobacterium and Flexibacter infections.

Seven bacterial species belonging to the Flavobacterium-Cytophaga group are currently considered to be pathogenic for fish. Because they were only recently described and/or because the disease they provoke has little economic significance, no study has been performed concerning immunization against Chryseobacterium scophthalmum, Flavobacterium johnsoniae and Flexibacter ovolyticus. Immunization with Flexibacter maritimus has not been investigated, and fish surviving a natural infection appear to remain equally susceptible to the disease during subsequent outbreaks. On the other hand, interesting data are available concerning immunization against Flavobacterium branchiophilum, Flavobacterium columnare and Flavobacterium psychrophilum because these bacterial species have been known for many years and are responsible for heavy losses in many countries. Surviving fish are usually protected against further infection by the same pathogens. Extensive serological studies have been performed and virulence mechanisms have also been investigated. The review of immunization trials against these three bacterial species shows important variations depending on the species of fish and the route of administration, but in several cases vaccinated fish were successfully protected by high titre of specific antibodies. However, no vaccine is commercially available.