Indigenous Lactic Acid Bacteria in Fish and Crustaceans - Aquaculture Nutrition: Gut Health, Probiotics and Prebiotics - page 140

whereas the presence of soybean meal led to enterococci (mostly Enterococcusfaecalis )levels
of log 2.8 and 3.1 CFU g −1 in MG and DI, respectively. Dimitroglou et al . (2009) investigated
the effect of mannan oligosaccharide (MOS) on the gut microbiota of juvenile rainbow trout
and observed that Enterococcus spp. increased (from 3% to 19% of the total culturable bacte-
rial population) in MOS-supplemented groups when compared with control groups. However,
when compared to the total bacterial community, clone libraries revealed that E. faecalis was
a minor component of the total bacteria community (1.8%) in the distal intestine of rainbow
trout fed a fishmeal based diet and was absent in trout fed a casein or soybean meal based
diet (Mansfield et al . 2010). More recently, pyrosequencing revealed that the total enterococci
abundance, comprising E. faecium , E . faecalis , Enterococcus hirae and Enterococcus mundtii ,
accounted for

0.1% of the sequences generated from the distal gut contents of rainbow trout
(Desai et al . 2012).
Moffit and Mobin (2006) isolated erythromycin-resistant Enterococcus spp. from Chinook
salmon reared in raceways, and Skrodenyte-Arbaciauskiene et al . (2008) observed that the
intestinal contents of Atlantic salmon contained isolates representing 11.5% of the culturable
heterotrophic bacteria which could not be differentiated between Enterococcus sp. U5-1 and
Lc . garvieae .

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6.3.7 Vagococcus
The genus Vagococcus was proposed by Collins et al . (1989) to accommodate some motile
Lancefield group N cocci, which were phylogenetically distinct from lactococci. Species of
this genus have been frequently isolated from diseased fish. In fact, Vagococcussalmoninarum
was originally isolated from diseased rainbow trout in North America (Wallbanks et al . 1990)
and, since then, has been recovered from Atlantic salmon, rainbow trout and brown trout with
peritonitis (Schmidtke and Carson 1994; Ruiz-Zarzuela et al . 2005). Although members of
the genus Vagococcus have been isolated from different sources (Jaffrès et al . 2010; Wang
et al . 2011), little is known about them as members of the normal intestinal microbiota in
salmonids. González et al . (2000) isolated LAB from the skin, gills and intestines of freshwa-
ter fish (mostly brown trout) and reported two isolates, which were identified as Vagococcus
fluvialis, , but no specific information was provided regarding the precise isolation source of
these strains.

6.3.8 Weissella
To our knowledge, no culture based studies have reported Weissella in the digestive tract of
salmonids; however, three recent culture-independent studies have reported indigenous Weis-
sella or Weissella -like populations in the GI tract of salmonids (Desai et al . 2012; Hovda
et al . 2012; Abid et al . 2014). In a study of triploid female rainbow trout fed different plant
based diets, Desai et al . (2012) reported Firmicutes with ca. 82-90% sequence similarity to
Weissella paramesenteroides (i.e. the nearest neighbour) in the distal gut contents. Weissella
cibaria has been identified from the GI tract of Atlantic salmon (Hovda et al . 2012) and brown
trout (Abid et al . 2014). There is no information on the levels of these species or their signifi-
cance to the host but recent studies have revealed that dietary application of W.cibaria reduced
intestinal Vibrio levels and elevated serum Ig levels of hybrid sorubims ( Pseudoplatystoma sp.)
(Mouriño et al . 2012). Weissella spp. have also been reported as opportunistic pathogens for
rainbow trout in China (Liu et al . 2009).