International Journal of Aquaculture, 2013, Vol.3, No.17, 92
-
100
http://ija.sophiapublisher.com
96
(40.57%)
followed by
A. caviae.
Nearly 10% of the
isolates were found to be
A. trota
and
A. veronii
.
Other
motile aeromonads included
A. hydrophila
,
A. jandaei
and
A. schubertii
.
A. sobria
associated with epizootic
ulcerative syndrome (EUS) has resulted in great
damage to fish farms in parts of Southeast Asia such
as Bangladesh and India (Rahman et al., 2002).
A.
sobria
,
has been identified as a causative agent of
disease in farmed perch
Perca fluviatilis
L. in
Switzerland (Wahli et al., 2005).
Aeromonas veronii
has been isolated from the ascitic fluid of Oscar
Astronotus ocellatus
showing signs of infectious dropsy
in India (Sreedharan
et al.,
2011).
Hatha et al., (2005)
reported
A. hydrophila
to be the predominant species
in the intestine of farm- raised fresh water fish
followed by
A. caviae
and
A. sobria.
In the present
study
A. sobria
was frequently encountered in the
intestinal samples of the ornamental fishes.
Motile
Aeromonas
species are ubiquitous bacteria in
aquatic environments. These bacteria can be found in
both polluted and unpolluted fresh water, in sewage,
in drinking water, private wells, in unchlorinated as
well as chlorinated water. In recent years, the presence
of
Aeromonas
spp. in municipal drinking water
supplies has become an emerging public health
problem (Haunninen, 1994). In the present study, in
terms of prevalence and abundance in water samples,
the most predominant species was found to be
Aeromonas sobria
(34.80%)
followed by
A. caviae
(16.57%).
Distribution of
A. hydrophila
and
A. veronii
was found to be equal (13.81%), while prevalence of
A. trota
,
A. jandaei
and
A
.
schubertii
were less than
10%.
A. schubertii
was the least predominant sp. in
both water and fish samples in our study,
A. caviae
was found to be second most predominant motile
aeromonad. High prevalence of
A. caviae
in water is
reported previously by Evangelista-Barreto et al. (2010).
In a study conducted in Turkey, Koksal et al., (2007)
reports the prevalence of
Aeromonas
such as
A.
hydrophila
(46%),
A. sobria
(34%),
A. caviae
(8%),
A.
veronii
(3%)
and
A. jandaei
(3%).
Rathore et al. (2005)
reports
A. hydrophila
to be the predominant sp. in
water and fish samples collected from aquaria in
India, which is contrary to our observations.
However, they also reported similar species such as
A. hydrophila, A. sobria
,
A. veronii. A. caviae
and
A.
schubertii,
though the relative prevalence of these
species was found to vary.
The pathogenesis of
Aeromonas
infections is
multifactorial, as aeromonads produce a wide variety
of virulence factors. Several virulence factors have
been studied in
Aeromonas
including aerolysin/hemolysin,
enterotoxins, proteases, lipases and deoxyribonucleases
(
Chopra et al., 2000; Janda, 2001; Chacón et al., 2003).
Nevertheless, it is apparent that some exo-enzymes are
important pathogenicity factors. The haemolytic and
proteolytic activities of motile and mesophilic
aeromonads were reported in most studies as
virulence-associated factors (Esteve et al., 1995;
Gonzalez-Serrano et al., 2002; Rahman et al., 2002).
The high rate of hemolytic activity detected in
Aeromonas
spp. is remarkable. The haemolytic
activity is strongly associated with enterotoxin
production in members of the genus
Aeromonas
(
Burke et al., 1983)
A. hydrophila
strains producing
cytotoxins, proteases and aerolysin were commonly isolated
from both healthy and moribund fish (Cahill, 1990).
Potentially pathogenic
Aeromonas
species are present
in diseased as well as healthy fish.
Widespread haemolytic, caseinolytic and gelatinolytic
activity was encountered among the motile
aeromonads isolated in the present study. These
factors were considered as pathogenicity markers by
(
Kozińska, 2007). The isolates obtained from healthy
fishes in this study are also potentially pathogenic as
revealed by the production of extracellular virulence
factors by the isolates. Though extracellular virulence
factors cannot be considered as definite marker for
pathogenicity of the isolates, the poor water quality
conditions of the aquaria maintained by local farmers
in this region might trigger disease outbreak by
opportunists. Shome et al. (1999) report that the
production of enzymes or toxins is not reflective of
biological virulence and they do not satisfy a strain to
be virulent or avirulent even though these appear to
enhance the disease process
in-vivo.
The whole
process of pathogenesis is a complex interaction
among the host, agent and environmental determinants.
Yucel et al., (2003) reports
A. hydrophila
and
A.
sobria
to be stronger producers of hemolysin, and
A.
caviae
strains to be non haemolytic
.
In the present
study also, A
.
sobria
,
A. hydrophila A. schubertii
and
A. jandaei
isolates from fish samples are 100%
haemolysin producers. Hatha et al. (2005) reports
100%
of
A. hydrophila
77.8%
of
A. caviae
and 50% of
A
.
sobria
isolated from fresh water fishes in South