Treatment Trial of Nile Tilapia (Oreochromis niloticus) Experimentally Infected with Vibrio alginolyticus Isolated from Sea bass (Dicentrarchus labrax).

BACKGROUND AND OBJECTIVE: In Egypt, Nile tilapia represents the main cultured type due to its economical price, palatability and easy culturing. This study was aimed to elucidate the pathogenicity of V. alginolyticus isolated from diseased sea bass and experimentally infected healthy Nile tilapia fish. MATERIALS AND METHODS: Healthy Nile tilapia fish were injected I/P with V. alginolyticus isolated from diseased sea bass. Symptoms and mortality rates of infected Nile tilapia fish were recorded during the experimental period. Re-isolation of V. alginolyticus was done from infected tilapia fish by bacteriological methods. For confirmation the pathogenicity of Vibrio isolated either from marine fish or tilapia fish, PCR test was done using tdh and bla gens. Liver and kidney function tests with histopathological examinations of some organs were performed. Treatment trial was done according to the antibiotic sensitivity test. RESULTS: The isolated Vibrio is highly pathogenic to Nile tilapia fish causing deterioration in all parameters which finished by severe mortalities. Treatment with florfenicol, enrofloxacin, or oxytetracycline reduced the mortality rate and improved liver and kidney function parameters of infected Nile tilapia fish. CONCLUSION: V. alginolyticus can infect both marine and fresh water fish inducing a high mortality rate. Treatment of infected fish with florfenicol, enrofloxacin, or oxytetracycline reduces the mortality rate.

Molecular Identification of Vibrio alginolyticus Causing Vibriosis in Shrimp and Its Herbal Remedy.

Penaeus monodon is highly susceptible to vibriosis disease. Aims of the study were to identify the pathogen causing vibriosis in P. monodon through molecular techniques and develop a biocontrol method of the disease by application of herbal extracts. Shrimp samples were collected aseptically from the infected farm and the bacteria were isolated from the infected region of those samples. Based on phenotypic identification, several isolates were identified as Vibrio sp. 16S rRNA gene sequences of the selected isolates exhibited 100% homology with V. alginolyticus strain ATCC 17749. An in vivo infection challenge test was performed by immersion method with V. alginolyticus where these isolates caused high mortality in juvenile shrimp with prominent symptoms of hepatopancreatic necrosis. Antibiogram profile of the isolates was determined against eleven commercial antibiotic discs whereas the isolates were found resistant to multiple antibiotics. A total of twenty-one herbal extracts were screened where Emblica officinalis, Allium sativum, and Syzygium aromaticum strongly inhibited the growth of V. alginolyticus in in vitro conditions. In in vivo conditions, the ethyl acetate extracts of E. officinalis and A. sativum successfully controlled the vibriosis disease in shrimp at a dose of 10 mg/g feed. This is the first report on molecular identification and biocontrol of V. alginolyticus in shrimp in Bangladesh.Penaeus monodon is highly susceptible to vibriosis disease. Aims of the study were to identify the pathogen causing vibriosis in P. monodon through molecular techniques and develop a biocontrol method of the disease by application of herbal extracts. Shrimp samples were collected aseptically from the infected farm and the bacteria were isolated from the infected region of those samples. Based on phenotypic identification, several isolates were identified as Vibrio sp. 16S rRNA gene sequences of the selected isolates exhibited 100% homology with V. alginolyticus strain ATCC 17749. An in vivo infection challenge test was performed by immersion method with V. alginolyticus where these isolates caused high mortality in juvenile shrimp with prominent symptoms of hepatopancreatic necrosis. Antibiogram profile of the isolates was determined against eleven commercial antibiotic discs whereas the isolates were found resistant to multiple antibiotics. A total of twenty-one herbal extracts were screened where Emblica officinalis, Allium sativum, and Syzygium aromaticum strongly inhibited the growth of V. alginolyticus in in vitro conditions. In in vivo conditions, the ethyl acetate extracts of E. officinalis and A. sativum successfully controlled the vibriosis disease in shrimp at a dose of 10 mg/g feed. This is the first report on molecular identification and biocontrol of V. alginolyticus in shrimp in Bangladesh.

Isolation and characterization of pathogenic Vibrio alginolyticus from sea cage cultured cobia (Rachycentron canadum (Linnaeus 1766)) in India.

Mass mortalities of cobia, Rachycentron canadum, sub-adults occurred during August 2013 in cage culture in the Gulf of Mannar, Mandapam Tamil Nadu, India. The epizootic of disease was started with typical classical clinical signs followed by acute mortality. Grossly, severe haemorrhage and congestion were observed in the gastric mucosa. The abdomen was distended with peritoneal fluid. The heart revealed haemopericardium and fibrinous pericardium. Histologically, the gastric mucosa showed severe erosion and necrosis. Haemorrhagic pericarditis and an increased size of the melano macrophage centre (MMC) in the tail kidney were other histopathological changes. Vibrio sp. was isolated from the gastric lesions and heart blood swab of moribund fishes and it was found to be virulent to the cobia fingerlings. After the challenge, the same bacterium could be re-isolated from moribund fingerlings. The 16S ribosomal RNA of the isolate was amplified and blast analysis of the sequence confirmed that the pathogen was Vibrio alginolyticus. The confirmation was also correlated with its cultural, biochemical and pathomorphological changes. This is the second report and the first incidence of epizootics with severe pathological lesions in cultured cobia in India. The study throws light on the pathology of vibriosis. By practising cage farm management measures, occurrences of infection may be prevented. SIGNIFICANCE AND IMPACT OF THE STUDY: The epizootics of vibriosis caused serious economic losses to farmers. Natural blooms of the pathogen can be prevented by sea cage management measures such as, changing the inner net of the cages, changing the location of the cages to relatively clean water (about 50 m apart) from the affected site and providing shade over the cages while the water temperature rises. Supplementation of the feed with immunostimulants and mineral mixture may be practised to improve the immune response against infection. Early diagnosis and sea cage management measures may prevent occurrences of the infection.

Oil-utilizing bacteria associated with fish from the Arabian Gulf.

AIMS: The objectives were to count and identify the oil-utilizing bacteria associated with fish, and to study their hydrocarbon-degradation potential. METHODS AND RESULTS: The standard dilution-plate method using a medium with crude oil as a sole source of carbon and energy revealed that 10 different fish sorts from the Arabian Gulf and two from fish farms accommodated millions of oil-utilizing bacteria per square centimetre of fish surface and per gram of gills and guts. According to their 16S rRNA sequences, those bacteria were affiliated to Psychrobacter, Vibrio, Planococcus, Pseudomonas and Actinobacterium. Planktonic and benthic biomass samples from the Gulf were also rich in oil-utilizing bacteria, but with different composition. All isolates could grow on n-alkanes from C(8) to C(40) and three representative aromatics as individual sole sources of carbon and energy. Quantitative analysis of hydrocarbons by gas-liquid chromatography revealed that the biomass samples of the individual bacteria could consume crude oil, n-octadecane and phenanthrene in liquid media. CONCLUSIONS: The abundant oil-utilizing bacterial associated with fish have the potential for cleaning oily waters. SIGNIFICANCE AND IMPORTANCE OF THE STUDY: Aquatic fauna accommodates rich consortia of oil-utilizing bacteria.

Immune stimulation and improved infection resistance in European sea bass (Dicentrarchus labrax) fed mannan oligosaccharides.

The objective of this study was to determine the effect of two levels of inclusion of mannan oligosaccharides derived from the outer cell wall of a select strain of Saccharomyces cerevisiae (Bio-Mos, Alltech Inc, USA) on growth, feed utilization, immune status and disease resistance of European sea bass (Dicentrarchus labrax). Specimens of 35 g at initial density of 3 kg/m3 were fed during 67 days at 0 per thousand, 2 per thousand and 4 per thousand dietary MOS level of inclusion in a commercial sea bass diet. Food conversion rate, specific growth rate, whole body biochemical composition, phagocyctic index of head kidney macrophages, NBT index, lysozyme and alternative complement pathway (ACP) activities as well as gut and liver histological structure were evaluated. Growth significantly increased at both MOS dietary inclusion levels. Histological features of the liver showed lower lipid vacuolization and regular-shaped morphology of hepatocytes around the sinusoidal spaces denoting a better utilization of dietary nutrients. No differences were found on gut histological evaluation. Statistical differences (P<0.05) on the phagocytic index were denoted with the inclusion of 4 per thousand Bio-Mos group. A positive correlation was found between the levels of lysozyme and alternative complement pathway activities in blood and the level of inclusion of MOS in diets. After the feeding trial, a cohabitation challenge test and direct gut inoculation were also performed with the pathogen Vibrio alginolyticus in a ratio 3:1. Twenty-one days post-challenge the number of cohabitant fish infected in the control group reached 33% comparing with none on the 0.4 per thousand MOS group. Finally, new fish were infected with V. alginolyticus by gut canalisation. After 24h post-infection no significant difference was denoted between groups and 48 h post-infection total infected fish in the control group was twice that of the 2 per thousand and 4 per thousand MOS groups.