Page 7 - IJA2014.Vol.4No.01

International Journal of Aquaculture, 2014, Vol.4, No.01
http://ija.sophiapublisher.com
4
Table 1 Antibiogram profile of gut LAB isolates from M. cephalus against selected fish and shrimp pathogens
Fish Pathogens Shrimp pathogens
Sl.
No.
Isolate
No. A. hydrophila P.
aeruginosa
V.
harveyi
V.
parahaemolyticus
V.
coralliilyticus
V.
fluvialis
V.
hollisae
V.
mimicus
V.
metschnikovii
1 155 +++ +++ ++ +++ ++ ++ - - -
2 156 +++ +++ ++ +++ ++ ++ +++ - ++
3 158 +++ +++ +++ ++ ++ ++ - - ++
4 159 +++ ++ +++ +++ ++ ++ - - ++
5 160 +++ +++ +++ +++ - - - - -
6 161 +++ +++ +++ +++ ++ + - - ++
7 168 +++ +++ +++ +++ - - - - ++
8 176 ++ ++ + +++ - - - - ++
9 177 +++ ++ ++ +++ ++ ++ - - ++
10 179 +++ +++ ++ +++ ++ ++ - - -
11 180 +++ +++ +++ +++ ++ ++ - - +++
12 229 ++ - - ND ++ ++ ++ - ++
13 240 - ++ - ND ++ ++ ++ - ++
14 243 ND ND ND ND ND ND ND ND ND
Note: (-): no zone of inhibition, (+): 5mm<zone<10mm, (++): 10mm<zone<15mm, (+++): zone > 15mm, (ND): not performed
Good antibacterial activity was also noticed against
various type strains of Escherichia coli and against the
Gram-positive bacterium; Bacillus cereus. The
antibacterial activity against several strains of
Salmonella ranged mostly between 5-15 mm but high
antibacterial activities; was noticed against Salmonella
oranienberg, Salmonella meleagridis and Campylobacter
jejuni 395; 5 out of 18, 2 out of 18 and 4 out of 18
respectively. On the other hand, moderate to good
activity was observed against V. cholerae strains V4
(by LAB 156, 159 and 240) and V129 by strain no.
LAB 156, 158 and 160. During the last two decades
there have been published several studies showing that
LAB inhibit growth of pathogenic Vibrio (Strøm,
1988; Olsson, 1995; Jöborn et al., 1997; Harzevili et
al., 1998; Ringø, 2008). StrØm (1988) reported in
vitro growth inhibition of Vibrio spp., Vibrio
anguillarum (the causative agent of classical
vibriosis), Vibrio salmonicida (the causative agent of
cold water vibriosis) and Proteus vulgaris. In two later
studies by Olsson (1995) and Jöborn et al. (1997) it
was demonstrated that an uncharacterized inhibitory
substances produced by Carnobacterium inhibens
inhibited the growth of V. anguillarum and
Aeromonas salmonicida; the causative agents of
furunculosis. In a more recent study, RingØ (2008)
tested the antibacterial activity of several LAB strains
against several fish pathogens; A. salmonicida, V.
anguillarum, V. salmonicida , V. splendidus, Moritella
viscosa (winter ulcer) and Carnobacterium
maltaromalticum. Of the shrimp pathogens tested in
the present study; Vibrio metschnikovii and Vibrio
hollisae displayed high degree of resistance against
the LAB isolates. Generally LAB strains isolated from
M. cephalus displayed distinctly higher antagonistic
activity against the fish pathogens tested compared to
the human and shrimp pathogens. This finding may be
due to the fact that, LAB strains were isolated from
fish gut, and we put forward the hypothesis that they
are better adapted at countering fish pathogens rather
than pathogens from shrimp and human sources.
However, this controversial hypothesis merits further
investigation.
2.2 Molecular diversity and biochemical properties
Isolates showing promising antimicrobial activity (14
No.s) were selected for the 16S rRNA analysis.
Lactobacillus brevis (35.7%) was the most
predominant (Table 3, Figure 1). It was noticed that L.
brevis strains (LAB 158, 159, 160, 169 and 180)
differed from each other in their ability to utilize
carbohydrate tested. LAB 158 and 160 matched in its
ability to utilize carbohydrate except esculin and LAB
169 showed positive to ribose and amygdalin. Isolate
LAB 156 identified to genus Lactobacillus, displayed
90% similarity to Lactobacillus casei ATCC 334 strain.