Indigenous Lactic Acid Bacteria in Fish and Crustaceans - Aquaculture Nutrition: Gut Health, Probiotics and Prebiotics - page 139

in a subsequent study (Perez-Sanchez et al . 2011b). More recently, Askarian et al . (2012)
isolated autochthonous Leu. citreum from PI of Atlantic salmon fed a diet supplemented with
5% chitin. This bacterium was further tested for digestive enzyme production but it did not
belong to the most promising enzyme-producing gut bacteria isolated.

6.3.5 Streptococcus
Species of the genus Streptococcus have been isolated from different sources, including fish.
However, the taxonomy of this genus has been the subject of important changes, because
several species have been reclassified into the Lactococcus , Enterococcus and Vagococcus
genera, based on biochemical characteristics, as well as molecular analyses (Schleifer and
Kilpper-Bälz 1984; Schleifer et al . 1985; Collins et al . 1989).
Streptococcus species were initially described as part of the intestinal microbiota in
salmonids by Trust and Sparrow (1974). Since then, this genus has been isolated from the
digestive tract of several fish species, including Arctic charr (Ringø 1993a; 1993b; Ringø
and Strøm 1994; Ringø and Olsen 1999; Ringø et al . 2002b), Atlantic salmon (Ringø et al .
2000; Bakke-McKellep et al . 2007) and rainbow trout (Spanggaard et al . 2000; Desai et al .
2012; Navarrete et al . 2012) (Table 6.1). Ringø et al . (2000) observed that streptococci
accounted for 0.6% of the culturable bacterial community isolated from the digestive tract
of Atlantic salmon. As is the case with other LAB, Streptococcus species also appear to be
affected by dietary treatment. In fact, Ringø et al . (2002b) observed that Streptococcus levels
in the hindgut of Arctic charr were log 4.3 and 3.6 CFU g −1 in fish fed diets supplemented
with soybean or marine oils, respectively; however, no streptococci were isolated in the
fish fed diets supplemented with linseed oil. Bakke-McKellep et al . (2007) observed that
diets containing soybean meal reduced culturable adherent Streptococcus spp. populations
in the MG and DI of Atlantic salmon to non-detectable levels, whereas the levels in the gut
of fishmeal fed fish were log 2.3 and 2.8 CFU g −1 in the MG and DI, respectively. Dietary
supplementation of inulin also promoted the establishment of Streptococcus spp. populations
in both intestinal regions.
More recently, Navarrete et al . (2012) identified Streptococcus sp. and Str. iniae in the DI
of rainbow trout using TTGE, and the study revealed that the streptococci populations could
be influenced by diet and the host fish genetics. Streptococcus infantarius subsp. infantarius ,
Streptococcusmitis and Streptococcuslutetiensis were recently observed as minor components
(i.e.

0.01%) of the distal intestinal microbiome of rainbow trout by pyrosequencing (Desai
et al . 2012).

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6.3.6 Enterococcus
Members of the genus Enterococcus , classified in the past as group D Streptococcus , have been
isolated from different sources, including salmonids (González et al . 2000; Bakke-McKellep
etal . 2007; Dimitroglou etal . 2009) (Table 6.1). González etal . (2000) sampled material from
the skin, gills and intestines of freshwater fish (mostly brown trout) and cultured isolates on BM
agar, which is a modified MRS medium with sodium acetate and ammonium citrate omitted,
for 36 h at 28 ∘ C. The results demonstrated that Enterococcus species, particularly Entero-
coccus durans , represented 3.2% of the culturable LAB. In contrast with Streptococcus levels,
Bakke-McKellep et al . (2007) observed that diets containing fishmeal or inulin reduced adher-
ent Enterococcus populations in the MG and DI of Atlantic salmon to non-detectable levels,