Colonization in the fish intestinal tract and production of inhibitory substances in intestinal mucus and faecal extracts by Carnobacterium sp. strain K1

Abstract

A non‐virulent Carnobacterium sp., designated strain K1, isolated from the gastrointestinal tract of Atlantic salmon, Salmo salar L., which produced inhibitory substances against bacterial fish pathogens, was examined in vitro for characteristics important for the colonization of the fish gastrointestinal tract and in vivo for persistence in the tract after oral dosing. In vitro growth experiments showed that the cells of this strain were metabolically active in both the intestinal mucus and faeces from salmonids. The production of growth inhibitors against the two common fish pathogens Vibrio anguillarum and Aeromonas salmonicida by Carnobacterium sp. strain K1 was demonstrated in vitro in mucus and faecal extracts. Furthermore, it was demonstrated that the Carnobacterium cells remained viable in the gastrointestinal tract for several days and that no detrimental effect to the fish was observed as a result of the presence of the bacterium.

Carnobacterium inhibens sp. nov., isolated from the intestine of Atlantic salmon (Salmo salar)

“…C. alterfunditum, C. mobile, C. divergens and C. gallinarum did not inhibit Vibrio anguillarum HI1 1360 or Aeromonas salmonicida ATCC 14174, but they inhibited the growth of strain KIT. As previously shown (Joborn et al, 1997), strain K I T suppresses the growth of Vibrio anguillarum and A . salmonicidu.…”

“…An atypical lactic acid bacteria, denoted strain KIT, was found during a screening of bacteria, from the intestine of Atlantic salmon (Salmo salar) (Joborn et al, 1997), which excrete substances which inhibit the growth of Vibrio anguillarum and Aeromonas salmonicida. The following organisms (EMBL accession numbers are in parentheses) were included in the construction of a phylogenetic tree : Carnobacterium alterfunditum (L08623), Carnobacterium divergens (X54270), Carnobacterium funditum (S86 170), Carnobacterium gallinarum (X54269), Carnobacterium mobile (X54271), Carnobacterium piscicola (X54268), Vagococcus J-luvialis (X54258) and Vagococcus salmoninarum (X54272).…”

“…Strain KIT has some unique characteristics previously not described for members of the genus Carnobacterium. Firstly, it produces growth inhibitors in vitro (Joborn et al, 1997) that suppress the growth of the bacterial fish pathogens Vibrio anguillarum and A . salmonicida, a property not found in the other Carnobacterium species tested (this study).…”

“…It can be hypothesized that these inhibitory bacteria may be able to prevent the colonization and proliferation of bacterial pathogens that invade the gastrointestinal tract of fish. A group of Lactobacillus -like bacteria were isolated during a screening procedure (Joborn et al, 1997) designed to select intestinal bacteria in Atlantic salmon (Salmo salar) with capacity to prevent the growth of the two common bacterial fish intestine of fish (Baya et al, 1991;Evelyn & McDermott, 1961 ;Humphrey et al, 1987;Knachel, 1981 ;Kvasnikov et al, 1977;Ringar, 1993;Ross & Toth, 1974;Schroder et al, 1980). However, the phylogeny of this group of bacteria needs to be investigated in more detail in order to arrive at a better understanding of their appropriate taxonomic assignments as well as their role in the gastrointestinal tract of fish.…”

“…The inhibitory activity and colonization potential of strain K 1 have previously been investigated (Joborn et al, 1997). In this paper, strain K I T is analysed by 16s rDNA sequence comparison and characterized by a range of biochemical and physiological tests.…”