Carnobacteria in fish

Carnobacterium is a genus of Gram-positive bacteria, within family Carnobacteriaceae, and they are catalase- and oxidase-negative, non-sporing bacteria with properties such as CO₂ and L (+)- lactic acid production from glucose, but they are not able to grow on acetate agar. They are ubiquitous lactic acid bacteria and have been isolated from both cold and temperate environments, and they are identified as components of the microbiota in the gastrointestinal (GI) tract of salmonids and several other fish species of which Carnobacterium (piscicola) maltaromaticum, Carnobacterium mobile, Carnobacterium divergens, Carnobacterium alterfunitum, and Carnobacterium inhibens are reported. During the last two decades several studies have revealed that carnobacteria can act as probiotics to promote health benefits of fish, as well as they in ex vivo studies to some extent can out-compete pathogens. In addition to beneficial effects, information is available that some carnobacteria species causing fish disease. The aim of the present review is to present an updated overview of Carnobacterium in fish, with focus on their presence in the GI tract, their use as probiotic supplement and general information on pathogenic carnobacteria.