Distribution, Extracellular Virulence Factors and Drug Resistance of Motile Aeromonads in Fresh Water Ornamental Fishes and Associated Carriage Water  

Nifty John , Mohamed Hatha Abdulla
Department of Marine Biology, Microbiology and Biochemistry, School of Marine Sciences, Lakeside Campus, Cochin University of Science and Technology, Cochin-682 016, Kerala, India
Author    Correspondence author
International Journal of Aquaculture, 2013, Vol. 3, No. 17   doi: 10.5376/ija.2013.03.0017
Received: 30 May, 2013    Accepted: 03 Jun., 2013    Published: 20 Jun., 2013
© 2013 BioPublisher Publishing Platform
This is an open access article published under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
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John, 2013, Distribution, Extracellular Virulence Factors and Drug Resistance of Motile Aeromonads in Fresh Water Ornamental Fishes and Associated Carriage Water, International Journal of Aquaculture, Vol.3, No.17 92-100 (doi: 10.5376/ija.2013. 03.0017)


During last decades there has been a continuous growth of aquaculture industries all over the world and taking into consideration the spurt in freshwater ornamental fish aquaculture and trade in Kerala, the present study was aimed to assess the prevalence of various motile Aeromonas spp. in fresh water ornamental fishes and associated carriage water. The extracellular virulence factors and the antibiogram of the isolates were also elucidated. Various species of motile aeromonads such as Aeromonas caviae, A. hydrophila, A. jandaei, A. schubertii, A. sobria, A. trota and A. veronii were detected. Aeromonas sobria predominated both fish and water samples. Extracellular enzymes and toxins produced by motile aeromonds are important elements of bacterial virulence. The production of extracellular virulence factors-proteases, lipase, DNase and haemolysin by the isolates were studied. All the isolates from both fish and water samples produced gelatinase and nuclease but the ability to produce lipase, caseinase and haemolysins was found to vary among isolates from different sources. Among the 15 antibiotics to which the isolates were tested, all the isolates were found to be sensitive to chloramphenicol, ciprofloxacin and gentamicin and resistant to amoxycillin. Local aquarists maintain the fish in crowded stressful conditions, which could trigger infections by the obligate/ opportunistic pathogenic members among motile aeromonads.

Ornamental fish; Motile aeromonads; Antibiotic resistance; Diseases

Keeping colourful and fancy fishes known as ornamental fishes, aquarium fishes, or live jewels is one of the oldest and most popular hobbies in the world.  The growing interest in aquarium fishes has resulted in a steady increase in aquarium fish trade globally. The global scope and scale of the ornamental fish trade and growing popularity of pet fish are strong indicators of the myriad economic and social benefits the pet industry provides. Culture of ornamental fish in the backyards of households requires very little space, skill and time, and has the potential to improve the economic condition of the household. ‘Earning a regular income, unlike seasonal work in agriculture, provides further motivation (Shaleesha and Stanley, 2000). Aquaculture is an emerging industrial sector which requires continued research with scientific and technical developments, and innovation. Over one billion ornamental fish comprising more than 4000 freshwater and 1400 marine species are traded internationally each year, making it one of the most important components of the global fish trade. Freshwater species make up 90% of this trade as they are the most popular and widely kept aquarium pets worldwide (Krishnakumar et al., 2009). The trade in ornamental (pet) fish is greater than 1 billion animals per year globally. More than 45 million fish per year are imported into the United Kingdom (UK) alone from a wide range of countries, in particular those in South East Asia (Wittington and Chong, 2007).

Fish diseases are a scourge of ornamental fish industry bringing huge economic loss. Bacterial organisms may be the primary cause of disease, or they may be secondary invaders. The majority of bacterial fish pathogens are natural inhabitants of the aquatic environment. Infections caused by motile members of the genus Aeromonas, are amongst the most common and troublesome diseases diagnosed in cultured warm water fishes and have been referred to by various names, including motile aeromonad septicemia (MAS), motile aeromonad infection (MAI), hemorrhagic 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 ofputative virulence factorsthat may play an importantrole 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 particularsymptoms 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 Aeromonas 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 and34.80% 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.

Figure 1 Distribution of Aeromonas spp. in fish and water samples

Prevalence of motile aeromonads at various parts of the body of fresh water ornamental fishes is given in Figure 2. A. hydrophila, A. veronii and A. jandaei were frequently encountered on gill surface when compared to body surface and intestine.

Figure 2 Distribution of Aeromonas spp. in the body surface, gill and intestine of fishes
1.2 Extracellular Virulence Factors of Aeromonas Species
All the isolates of Aeromonas spp. obtained exhibited gelatinase and DNase activity. All the isolates of Aeromonas sobria exhibited caseinase and β haemolysin production. Similarly all the isolates of A. hydrophila and A. jandaei were capable of producingβ haemolysin. β haemolysin production was infrequent in A. caviae. Lipase was produced by all the isolates of A. hydrophila, A. jandaei and A. veronii but theirproduction among the isolates of other spp. varied. The production of extracellular virulence factors by the Aeromonas isolates obtained from fish and water samples are given Table 1 and Table 2 respectively.

Table 1 Prevalence of extracellularvirulence factors among motile aeromonads from ornamental fish samples

Table 2 Prevalence of extracellular virulence factors among motile aeromonads from carriage water samples
1.3 Antimicrobial Resistance
All the aeromonad isolates tested were resistant to amoxycillin and sensitive to ciprofloxacin, chloramphenicol and gentamicin regardless of their source. While all the Aeromonas isolates from water were sensitive to nitrofurantoin, 1.14% of isolates from fish samples was resistant to nitrofurantoin. Resistance to ceftazidime was found in 13.33% of A. veronii and 5.63% of A. sobria isolates from fish samples and 8% of A. veronii isolates from water samples. All the other isolates were sensitive to this antibiotic. All the isolates except 3.63% of A. caviae from fish samples and 20% of A. hydrophila, 12.69% of A. sobria and 8% of A.veronii from water samples were sensitive to sulfafurazole.Resistance exhibited to other antibiotics by the isolates from fish and water samples are given in Table 3 and Table 4 respectively.

Table 3 Antibiotic resistance of motile aeromonads from fish samples

Table 4 Antibiotic resistance of motile aeromonads isolates from water samples

2 Discussion
The prevalence and distribution of bacteria belonging to the genus Aeromonas in aquatic environments is of great public health concern since Aeromonas spp. can cause infections and epizootics in a variety of animals. Motile aeromonads have been recognized as occasional pathogens of cultured fishes and the most common bacteria in freshwater habitats throughout the world. It is the etiological agent for motile aeromonad septicaemia (MAS) in fish. Aeromonas has also been frequently isolated from the lesions of epizooticulcerative syndrome (EUS) fishes (Torres et al., 1990; Subasinghe et al., 1990; Roberts et al., 1990). This disease isa serious threat to the freshwater fish production of Southeast Asian countries. Itcauses mass mortalities in both cultured and wild fish species every year.The prevalence of different species of Aeromonas is likely to vary with geographical locations. In the present study Aeromonas sobria was the predominant species isolated from fish samples (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 (Sreedharanet 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,
International Journal of Aquaculture
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