International Journal of Aquaculture, 2013, Vol.3, No.17, 92
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India to be β haemolytic.
Equal distribution of α and β haemolytic activity
among the
A. hydrophila
isolates from fish samples in
India, was reported earlier (Illanchezian et al., 2010).
While around 90% of
A. veronii
and
A. trota
isolated
in the present study were able to produce haemolysin,
only 72% of
A. caviae
had this capability. All the
isolates in the present study produced gelatinase and
nuclease. Similarly all
A. sobria
isolates were capable
of elaborating caseinase. In general, caseinase
production potential was widespread among most of
the motile aeromonads encountered in this study.
Castro-Escarpulli et al. (2003) observed comparable
levels of extracellualr virulence factors among the
motile aeromonads from frozen fish samples in
Mexico. In contrast to their finding, in the present
study 100 % of
A. hydrophila, A. veronii
and
A.
jandaei
isolates are lipase producers. Possibility of
caseinolytic (Mateos et al., 1993) and gelatinolytic
activity (Shome et al., 1999) with virulence is
substantiated by the above research groups who
observed that all the
A. hydrophila
isolates from
diseased fishes with dropsy and EUS had caseinolytic
and gelatinolytic activity.
All the isolates from the water samples in the present
study are producers of gelatinase and nuclease. β
haemolysin was produced by 100% of
A. hydrophila
and
A. sobria
(
Tables 1 and 2). β haemolytic activity
among all the isolates of
A. hydrophila
and
A. sobria
and α haemolytic activity among all the isolates of
A.
caviae
from water sample are reported earlier (Gibotti
et al
.,
2000).
The extracellular virulence factors
among Aeromonas
spp. isolated from Bhavani river,
South India was studied by Bagyalakshmi et al. (2009).
Several of these virulence factors have been identified
in strains isolated from water (Sechi et al., 2003). In
the present study also, all these virulence factors have
been identified in strains isolated from water.
There have been conflicting reports on the
susceptibility of motile Aeromonads to commonly
used antibiotic agents. High level of resistance against
amoxycillin, and carbenecillin and 100% sensitivity to
chloramphenicol, ciprofloxacin and gentamicin was
noticed in the isolates from both fish and water
samples. Motile aeromonads isolated from fish and
water samples, in India exhibiting 100% sensitivity to,
ciprofloxacin and gentamicin and high level of
susceptibility to chloramphenicol is reported by
Rathore et al. (2005). Complete sensitivity to
chloramphenicol, ciprofloxacin and gentamicin by the
isolates is reported by Penders and Stobberingh (2008).
All the isolates from water samples in the present
study were susceptible to nitrofurantoin and only a
3.63%
of
A. caviae
isolates from fish samples
exhibited resistance to the antibiotic. High level of
susceptibility to nitrofurantoin by the isolates is also
reported by Castro-Escarpulli et al. (2003) but in
contrast to our finding he has reported 100%
sensitivity to nalidixic acid and more than 50%
resistance to gentamicin and varying degrees of
resistance to chloramphenicol and ciprofloxacin.
Among the motile aeromonads isolated from fish
samples in India, relatively low level (<10%) of
resistance to nalidixic acid, gentamicin and
ciprofloxacin is reported by Hatha et al., (2005).
However, resistance to nalidixic acid was considerably
high among the motile aeromonads encountered in the
present study (49.71%), while all the isolates were
sensitive to gentamicin and ciprofloxacin. Varying
levels of resistance to nalidixic acid, gentamicin and
ciprofloxacin has been reported among motile
aeromonads from water samples (Koksal et al., 2007;
Evangelista-Barreto et al., 2010). Similar to the
findings of these researchers, we also observed
complete sensitivity of our isolates to nitrofurantoin,
chloramphenicol and ciprofloxacin. The development
of antibiotic resistant strains is a great extent attributed
to the misuse of antibiotics in culture systems for
treatment and for better feed conversion, these levels
are bound to vary according to local practises.
Resistance to ceftazidime among the isolates from
water and fish are found to vary from 8 to 15% among
A. veronii
and
A. sobria
.
Except 3.63% of
A. caviae
isolates, all the other aeromonad isolates from fish
samples were susceptible to sulfafurazole. While all
A.
caviae
isolates from water were susceptible to
sulfafurazole, 12.69% of
A. sobria,
8%
of
A. veronii
and 20% of
A. hydrophila
isolates were resistant to
this drug. Resistance to trimethoprim was found to vary
among the different species of motile aeromonads such
as
A. caviae, A. hydrophila
A. trota
from fish samples,
however all the isolates of
A. trota, A. jandaei
and
A.
schubertii
from water was sensitive to this drug.