Abstract
Background and Aim:Aeromonas hydrophila is a major cause of bacterial infections affecting a wide range of warm water fishes worldwide. In Malaysia, A. hydrophila isolations from diseased fishes were previously reported; however, with limited information. The present study investigates the antibiotic susceptibility and pathogenicity of A. hydrophila isolated from farmed red hybrid tilapia (Oreochromis spp.) in Malaysia.Materials and Methods:A. hydrophila was biochemically identified and subjected to antibiotic susceptibility tests. The isolate was then intraperitoneally injected into red hybrid tilapia, and the mortality, clinicopathological changes, and LD50 were determined up to 240 h post-infection (hpi).Results:The isolate demonstrated multiple antibiotic resistances (MAR) toward amikacin, ampicillin, cefotaxime, amoxicillin, trimethoprim-sulfamethoxazole, erythromycin, and streptomycin, with a MAR index of 0.5. The experimental infection of A. hydrophila at 105 CFU/mL in the red hybrid tilapia resulted in 100% mortality at 240 hpi. The LD50 was determined at 1.1×104 CFU/mL. Infected fish demonstrated occasional erratic swimming patterns, localized hemorrhages and depigmentation on the body and operculum areas, fin erosion, enlargement of the gall bladder, and hemorrhage in internal organs. Microscopic observation of infected fish revealed brain congestion, tubular necrosis, and glomerular shrinkage in the kidneys, necrosis of hepatocytes, and congestion of blood vessels in the liver.Conclusion:The high virulence of A. hydrophila to the red hybrid tilapia emphasizes the importance of active, on-going monitoring of its prevalence in Malaysian tilapia farming.
Highlights
Tilapia (Oreochromis spp.) is among the major commercially important freshwater fish intensively farmed worldwide
The experimental infection of A. hydrophila at 105 CFU/mL in the red hybrid tilapia resulted in 100% mortality at 240 hpi
The A. hydrophila isolate in this study formed yellowish, opaque colonies on Tryptic Soy Agar (TSA) agar, produced beta-hemolysis on horse blood agar, and were motile, oxidase- and catalase-positive, and Gram-negative short rods (Table-1)
Summary
Tilapia (Oreochromis spp.) is among the major commercially important freshwater fish intensively farmed worldwide. World tilapia production has exceeded 5 million tonnes, generating incomes of approximately USD 9.8 billion in 2015, and has been increasing annually [1]. In Malaysia, the production of tilapia in 2017 was approximately 31,400 tonnes with a wholesale value of RM 286 million, which indicates the significance of tilapia farming in the country [2]. In Malaysia, A. hydrophila isolations from diseased fishes were previously reported; with limited information. The present study investigates the antibiotic susceptibility and pathogenicity of A. hydrophila isolated from farmed red hybrid tilapia (Oreochromis spp.) in Malaysia
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