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the level of
Pseudomonas
spp. and the observation that
Carnobacterium
sp. PT220 was only
isolated in fish fed
P. acidilactici
. After 5 months feeding on the experimental diets,
P. acidi-
lactici
levels declined to ca. log 0.9 ± 0.6 CFU g
-1
in the probiotic group. The indigenous
bacterial levels were significantly lower in the
P. acidilactici
fed fish than in the control, and
autochthonous yeast levels were detected at low levels (log 0.6 ± 0.6 CFU g
-1
)inthe
P. acidi-
lactici
fed fish but were not detected in the control group. The composition of the indigenous
autochthonous microbiota was distinctly different and less diverse than that sampled from
fish after 20 days experimental feeding, with
Carnobacterium
sp. PT220 dominating both fish
groups at 5 months. However, as the fish were starved for 24 h prior to sampling the probiotic
values reported may not be a true representation of the precise levels during the feeding periods.
(Merrifield
etal
. (2011) fed rainbow trout either vegetative or lyophilized
P.acidilactici
cells
incorporated into a basal diet at either 10
7
or 10
8
CFU g
-1
for a period of 10 weeks. Total viable
counts of indigenous microbiota associated with the posterior mucosa increased marginally
from log 3.60 CFU g
-1
in the control fish to log 3.75-4.63 CFU g
-1
in the probiotic fed fish.
Total viable levels of posterior allochthonous microbiota did not differ significantly between
groups, ranging from ca. log 8 CFU g
-1
in the control group to ca. log 7.5-8.5 CFU g
-1
in pro-
biotic fed groups.
P. acidilactici
were absent in the control group but successfully populated
the posterior intestine (as both epithelium associated and transient lumen populations) in all
probiotic groups with no significant differences between vegetative or lyophilized treatments.
Digesta based
P. acidilactici
levels were considerably higher than the epithelium based popu-
lations (levels approaching log 6 CFU g
-1
) but again no significant differences were observed
between dietary levels or supplementation forms. Scanning electron microscopy revealed the
presence of
P. acidilactici
-like cells on the intestinal epithelium, particularly at the bases
between mucosal folds. Similar results were reported in another rainbow trout study which
demonstrated
P. acidilactici
populations on the mucosa of the stomach, proximal intestine
and distal intestine (Merrifield
et al
. 2010b) as well as elevated microvilli length in the prox-
imal intestine and increased endocytic activity in the proximal intestine and distal intestine.
The effect of this probiotic on the rainbow trout epithelial structure was further studied using
the
ex vivo
intestinal sac method, with or without the co-incubation of
Vibrio anguillarum
(Harper
et al
. 2011). DGGE and sequence analyses revealed the presence of these bacteria on
the intestinal epithelium after exposure. Although the probiotic was not shown to antagonize
the pathogen directly, it did outcompete it, reduce the epithelial pathogen induced damage to
some extent, and elevate levels of goblet cells and intraepithelial leukocytes.
The effect of
P. acidilactici
on the gut microbiota of tilapia was reported by Ferguson
et al
. (2010). After feeding dietary
P. acidilactici
at log 7 CFU g
-1
to tilapia for 32 days,
DGGE fingerprints revealed that dietary
P. acidilactici
significantly affected the composition
of the intestinal microbial communities as microbial profiles of the probiotic fed fish clus-
tered into a group distinctly different to that of the gut microbiota of the control group and
the microbiota of the initial fish (Figure 8.3). The probiotic fed fish displayed lower bacterial
species richness and diversity which indicated that the probiont outcompeted some indige-
nous bacterial populations. Although total culturable aerobic and anaerobic levels within the
gut were not affected, the LAB levels were significantly higher in the probiotic group (log
7.5 CFU g
-1
, ca. 10% of the cultured population) than in the control group (log 4 CFU g
-1
,
<
0.01% of the cultured population). 16S rRNA sequence analysis confirmed the isolates from
the probiotic group as
P. acidilactici
. The probiotic was observed to be present for at least 17
days after reverting the probiotic fish to a control diet, and during this period DGGE revealed
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