Indigenous Lactic Acid Bacteria in Fish and Crustaceans - Aquaculture Nutrition: Gut Health, Probiotics and Prebiotics - page 138

sp. U5-1 represented 11.5% of the culturable heterotrophic bacteria of Atlantic salmon. Pérez
et al . (2011) proposed a new subspecies, Lc. lactis subsp. tructae , which was isolated from the
intestinal mucus of brown trout ( Salmo trutta ) and rainbow trout.
In 2008, Itoi and colleagues put forward the controversial hypothesis that since Lc . lac-
tis has rarely been isolated from marine environments, the cells may enter into a viable but
non-culturable state. This hypothesis merits further evaluation. In their study on Lc . lactis
subsp. lactis isolated from the GI tract of marine and freshwater fish, Itoi et al . (2009) revealed
extensive diversity in phenotypic variation and suggested that the strain(s) isolated from the
intestine of fish may be useful as probiotics in aquaculture as the bacterium seems to adapt to
various environments. Indeed, some information is also available on the probiotic properties
of selected Lactococcus strains. Balcázar et al . (2007b) characterized two Lc. lactis strains,
Lc. lactis subsp. lactis (CLFP 100) and Lc. lactis subsp. cremoris (CLFP 102), isolated from
the intestinal microbiota of rainbow trout. Both strains showed high adhesion to fish intestinal
mucus and reduced the mucus adhesion success of fish pathogens, such as A. salmonicida ,
C. maltaromaticum , Lc. garvieae and Y. ruckeri . The ability to adhere to mucosal surfaces
is an important factor in the competitive exclusion of pathogens, and adhesion to the intesti-
nal mucosa has been suggested to enhance the ability to stimulate the immune system. In
fact, Balcázar et al . (2007c) observed a correlation between colonization with Lc. lactis and
non-specific humoral responses such as alternative complement pathway activity and lysozyme
activity in brown trout. Besides inducing enhanced immune responses, Lc.lactis exhibited pro-
tection against furunculosis in rainbow trout (Balcázar et al. 2007b) and brown trout (Balcázar
et al . 2009).
6.3.4 Leuconostoc
Species of the genus Leuconostoc have been frequently isolated from several food prod-
ucts such as dairy and meat products, vegetables, and fermented food (Hemme and
Foucaud-Scheunemann 2004). However, limited information is available on the presence of
Leuconostoc species in salmonids (Ringø and Strøm 1994; Ringø et al . 1998; Balcázar et al .
2007b; 2009; Askarian et al . 2012). Ringø and Strøm (1994) showed that approximately 4.5%
of the cultivable microbiota in the faeces of Arctic charr fed a capelin ( Mallotus villosus )roe
diet belonged to the genus Leuconostoc . In a later study, Ringø et al . (1998) isolated several
Leuconostoc species associated with the epithelial mucosa of the stomach, PI and DI of Arctic
charr fed different polyunsaturated fatty acids. Unfortunately, no attempt was made to identify
the Leuconostoc to species level by 16S rRNA gene sequencing in the studies of Ringø and
Strøm (1994) and Ringø et al . (1998). Mansfield et al . (2010) identified Leuconostoc citreum
as a minor component of the total bacteria community in the distal intestine of rainbow trout
fed a fishmeal based diet. However, this community, equivalent to 2.3% of the clones derived
from the fishmeal fed fish, was not present in fish fed a diet whereby the protein was derived
from casein or soybean meal.
Balcázar et al . (2007b) isolated a Leuconostoc mesenteroides strain (CLFP 196) from the
intestinal microbiota of rainbow trout, which produced antibacterial compounds against sev-
eral fish pathogens. Further studies demonstrated that administration of this strain enhanced
the immune response and disease resistance of rainbow trout (Balcázar etal . 2007b) and brown
trout (Balcázar et al . 2009). Perez-Sanchez et al . (2011a) isolated Leu. mesenteroides subsp.
mesenteroides from the intestine of rainbow trout, and although this strain showed some posi-
tive invitro characteristics it failed to improve rainbow trout disease resistance to lactococcosis