International Journal of Aquaculture, 2013, Vol.3, No.17, 92
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100
http://ija.sophiapublisher.com
93
septicemia, red pest, and red sore.
Aeromonas
bacteria
causing these infections are called aeromonads
(
Camus et al., 1998).
Aeromonas
infections are a
serious threat to fresh water fish production, bringing
enormous economic loss to ornamental fish industry.
The detection of virulence factors in
Aeromonas
is a
key component in the determination of potential
pathogenicity, because more than two virulence
factors act multifunctionally and multifactorially it
seems necessary to continue surveying the distribution
of known virulence determinants in currently
circulating
Aeromonas
strains.
The disease problems are treated with antibiotics, the
indiscriminate use of which can result in the rapid
spread of multi-drug resistant pathogens across the
system. It is also important for the ornamental fish
industry to recognize the extent to which the bacteria
associated with ornamental fish have developed
antimicrobial resistance. This fact along with the
financial crisis caused by the mortality of ornamental
fishes makes the study of different geographical
isolates of aeromonads important.
Aquaculture is in a phase of rapid growth and
development. Fish diseases are among the most
important problems and challenges confronting fish
culturing. Among the etiological agents of bacterial
fish disease, the motile
Aeromonas
group is
considered important.
Aeromonas
spp. is ubiquitous in
natural waters and comprises mesophilic motile and
psychrophilic non motile gram-negative bacteria.
Worldwide studies have demonstrated that
Aeromonas
spp. are universally distributed and widely isolated
from clinical, environmental and animal sources, food
samples and aquatic environment (Janda and Abbott,
2010).
In aquatic environments, they are found in
ground water, surface water, estuarine environments,
sewage effluents, lakes and rivers (Galindo and
Chopra, 2007) and in public drinking water and tap
water (Pablos et al., 2009; Kivanc et al., 2011).
The widespread distribution of these bacteria in the
aquatic environment and the stress induced by
intensive culture practices predisposes fish to
infections. A number of putative virulence factors that
may play an important role in the development of
disease, have been described in several species of the
genus
Aeromonas,
which includes haemolysins,
cytotoxins, enterotoxins, proteases, lipases, DNases
and adhesins (Sen and Rodgers, 2004). The
pathogenesis of
Aeromonas
infections is multifactorial,
and no single virulence factor can be unequivocally
pinpointed as responsible for particular symptoms or
disease stages. Pathological conditions attributed to
members of the motile aeromonad complex may
include dermal ulceration, tail or fin rot, ocular
ulceration, hemorrhagic septicemia and scale
protrusion disease. Outbreaks of motile aeromonad
septicaemia can reach epidemic proportions in farmed
aquatic animals, with high rates of mortality (Liles et
al., 2011). The disease problems are treated with
antibiotics, but the emergence of antibiotic-resistant
bacteria imposes a substantial burden on aquaculture.
Antibiotic resistance is particularly relevant in
pathogenic
Aeromonas
species in which, besides the
classical resistance to β-lactam antibiotics,
multiple-resistance has been frequently identified
(
Goñi-Urriza et al., 2000; Vila et al., 2002; 2003).
These bacteria can receive and transfer antibiotic
resistance genes to other Gram negative bacteria
(
Marchandin et al., 2003).
Diseases in intensive freshwater aquaculture have
brought great economic loss to India in recent years.
Infections due to
Aeromonas
are common and pose a
threat to the development of the aquaculture enterprise.
Therefore the present study was carried out to assess
the prevalence of various motile A
eromonas
spp. in
fresh water ornamental fishes and associated carriage
water. The extracellular virulence factors and the
antibiogram of the isolates were also studied.
1
Results
1.1
Distribution of
Aeromonas
Species
Motile
Aeromonas
spp. was isolated from ornamental
fish samples and associated carriage water samples.
One hundred and seventy five isolates from the fish
samples and one hundred and eighty two isolates from
the water samples were characterized to species level,
Aeromonas sobria
predominated in both cases -
40.57%
in fish samples and
34.80%
in water samples.
A. caviae
was the second dominant spp. in both
samples but its percentage of occurrence was much
higher in fish samples, (31.43%), when compared to
water samples (16.57%).
A. hydrophila, A. jandaei, A.
schubertii
and
A. veronii
predominated in water samples
when compared to fish samples as shown in Figure 1.