Agriculture Reference
In-Depth Information
in the intestinal contents and intestinal mucus, respectively. Furthermore, C. divergens strains
(originally isolated from the intestines of Atlantic cod and Atlantic salmon: Strøm 1988) have
been reported to populate the mucus/mucosa of Atlantic cod fry (Gildberg and Mikkelsen
1998). C. divergens werefedtofryat10 8 CFU g -1 , with and without the addition of a fish
protein hydrolysate immuno-stimulating peptide, for 3 weeks. Both C. divergens strains suc-
cessfully survived transit through the entire GI tract as LAB levels were recovered in the faeces;
however, these levels were only approximately 1% of initial dietary levels. LAB levels in the
pyloric caeca samples were observed at log 3-4 CFU g -1 tissue and histochemistry verified
the presence of C. divergens in the internal mucus layer. Levels in the intestine however were
lower and less frequently detected in the samples. The study suggests that the pyloric caeca
may be a more favourable site for colonization than the intestine, and the authors suggested that
there seemed to be no host specificity (i.e. specificity of probionts derived from the host) with
preference for GI colonization as the strain previously isolated from Atlantic salmon displayed
better colonization than the strain previously isolated from Atlantic cod.
Two studies have investigated the effect of C.divergens application, via rearing water, on the
gut microbiota of fish larvae. In a preliminary study with 5-day-old Atlantic cod larvae, Strøm
and Ringø (1993) evaluated the effect of inoculating rearing water with C.divergens (described
as Lb . plantarum in this study but later reclassified as C.divergens by Ringø etal. 2001) which
was originally isolated from the gut of adult Atlantic cod and produced a substance that inhib-
ited the in vitro growth of the fish pathogens Vibrio ( Listonella ) anguillarum , Vibrio salmoni-
cida and Vibrio sp. (Strøm 1988). By exposing the cod larvae to C. divergens the cultivable
bacterial population level was significantly reduced and the composition was also affected. In
larvae exposed to the probiotic, C. divergens accounted for 70% of the cultivable microbiota
and Pseudomonas spp. accounted for 20%, while Aeromonas spp. and bacteria belonging to
the Cytophaga / Flexibacter group were detected in the control group but were not detected
in larvae exposed to C. divergens . Whether this modulation in the gut microbiota had any
effect on larval growth or health was however not investigated. Following this, Ringø (1999)
investigated if C . divergens isolated from the gut of Atlantic salmon (Strøm 1988) was able to
attach to the mucosal surface and colonize the gut of turbot ( Scophthalmus maximus L.) lar-
vae. Vibriopelagius , originally isolated from turbot larvae, was used as a control and an ELISA
was used to determine bacterial levels. When larvae were exposed to V. pelagius the bacteria
was detected in larvae 3 days post hatching (dph), while C . divergens was detected in larvae
exposed to C . divergens , and when in combination with V . pelagius , at 6 dph. Based on these
results the author concluded that C . divergens , originally isolated from the GI tract of Atlantic
salmon, was able to attach to and colonize the gut of turbot larvae at the time of hatching.
The present studies indicate that Carnobacterium spp. are resistant to specific conditions
within the GI of salmonids, Atlantic cod and turbot (i.e. proteolytic enzymes, low pH, bile
acids and pancreatic juice) and appear to be effective at competing with indigenous microbes
within the gut. However, there appear to be differences in the efficacy of strains to populate
the mucosa, and the reasons for this have not been comprehensively determined as specificity
of strains does not necessarily correlate to their original isolation source (i.e. fish species).
Carnobacteria, particularly C. divergens strains, appear to be good candidates to populate the
intestinal mucus and modulate the gut microbiota of cold water fish species; they are likely
to be far less effective in warm water species where their slower growth rates are likely to
render them unable to outcompete many of the faster growing components of the indigenous
microbiota. However, Gopalakannan and Arul (2011) reported that during probiotic feeding
Search WWH ::




Custom Search