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International Journal of Aquaculture, 2014, Vol.4, No.01
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6
Table 4 Effect of temperature and different concentrations of NaCl on gut associated LAB from
M. cephalus
Growth at
Different temperature (
℃
)
Growth at
NaCl concentration (%)
Sl. No
LAB isolate
4
10
15
37
45
4
6
8
10
1
155
+
+
+
+++
+
++
++
+
-
2
156
+
+
++
+
+
++
++
+
-
3
158
+
+
+++
+++
+
++
+
+
-
4
159
+
+
+
++
++
+
+
+
-
5
160
+
+
+++
++
+
++
+
+
-
6
161
+
+
+++
+++
+
++
+++
+
-
7
168
+
+
+++
+++
+
++
+
+
-
8
176
+
+
++
+++
+
++
+
+
-
9
177
+
+
+
+++
+
+++
++
+
-
10
179
+
+
+++
+++
+
+
+
+
-
11
180
+
+
++
++
++
+
+++
+
-
12
229
*
*
*
*
*
*
*
*
*
13
240
*
*
*
*
*
*
*
*
*
14
243
*
*
*
*
*
*
*
*
*
Note: (+++): O.D value more than 1.0, (++): O.D value 0.5 to 1.0, (+): O.D value less than 0.5, (-): No Growth, (*): Unviable
Isolate LAB 155, 156, 158,159, 160 and 161 were
catalase-positive even though they have been
identified to belong to genus
Lactobacillus,
which are
generally catalase negative. However, according to the
classification by Kandler & Weiss (1986) some strains
are weak catalase positive. Twelve isolates out of the
14 for which 16S rRNA analysis was performed,
belonged to the genus
Lactobacillus
. In a previous
study Nagvenkar et al. (2006)
studied the gut
microbiota of
M. cephalus
and reported the presence
of
Pseudomonas
sp.,
Vibrio
sp.,
Streptococcus
sp.,
Enterobacter
sp.,
Vibrio
parahaemolyticus
,
Bacillus
subtilis
,
Serratia
marcescens
and
Proteus
vulgaris
.
However no LAB was isolated. In the present study,
growth studies of LAB were conducted at different
temperatures and at different concentrations of NaCl
and displayed that the LAB isolates grew well
between 15-37
℃
and at 0 to 6% NaCl (Table 4).
These results are in accordance with the results
reported by Abegaz (2007) where all LAB grew at 10,
15 and 37
℃
and in 4 and 6% NaCl.
LAB peptides like bacteriocin offer us a plausible
option vis-à-vis antibiotics: they are effective in
nanomolar range, are non-toxic and easily broken
down by proteolytic enzymes (Ogunbanwo et al.,
2003). The isolates used in the present study displayed
wide antibacterial activity, smallest spectrum of
inhibition being 6 out of 29. It is proposed that isolate
LAB 156;
Lactobacillus
casei
(GenBank accession
no: KJ156316) which displayed antagonistic activity
against 25 out of 29 test strains of the test pathogens
might be used as a probiotics in the future; but further
studies are needed. It can be concluded that, LAB
isolated from the gut of
M. cephalus
provide an
opportunity to develop a sustainable and organic
means of combating the aquaculture pathogens. It has
been demonstrated by Balcázar (2003) that a mixture
of bacterial strains (
Bacillus
and
Vibrio
sp.) had a
beneficial effect on the growth and survival of
juveniles of white shrimp besides improving their
immunity against
Vibrio harveyi
and white spot
syndrome virus. It was also demonstrated that
nonspecific immune system could be activated by
Clostridium butyricum
in rainbow trout fishes against
vibriosis (Sakai et al., 1995). (Nikoskelainen et al.,
2003) stimulated respiratory burst in rainbow trout by
the administration of lactic acid bacteria
Lactobacillus
rhamnosus
(strain ATCC 53103). It may not be
possible to replace the usage of antibiotics altogether,
but probiotic can definitely reduce the consumption of
antibiotics as they can provide disease resistance to
the host.
Acknowledgement
We thank the University Grants Commission, New
Delhi, India, for providing us with the necessary
financial support to carry out the present study.