First case of Aeromonas schubertii infection in the freshwater cultured snakehead fish, Ophiocephalus argus (Cantor), in China

An epizootic in snakehead fish, Ophiocephalus argus, in earthen ponds in Xianning, Hubei Province, central China, from June to August 2009 was found to be caused by Aeromonas schubertii. The cumulative mortality within 40 days was 45%, and the diseased fish were 18 months old and 3545 cm in length. Multiple, ivory-white, firm nodules, 0.51 mm in diameter, were scattered throughout the kidney. Blood clots, 35 mm in diameter, were found in the liver. This is a disease frequently found in cultured snakehead throughout China. Isolated bacteria were Gram negative, facultatively anaerobic, motile, short rod-shaped, with a length of 0.31.0 mu m. Morphological and biochemical tests, as well as phylogenetic analysis derived from 16S rRNA, gyrB, rpoD and dnaJ gene sequencing all strongly indicated that these snakehead isolates are identical to A.similar to chubertii. In addition, the isolates possessed two plasmids: 5.0 kb and 10.0 kb. Antibiotic sensitivity testing of the isolates was carried out by the standard KirbyBauer disc diffusion method. Experimental infection assays were conducted, and pathogenicity (by intraperitoneal injection) was demonstrated in snakehead fingerlings and zebrafish, Brachydanio rerio (Hamilton).An epizootic in snakehead fish, Ophiocephalus argus, in earthen ponds in Xianning, Hubei Province, central China, from June to August 2009 was found to be caused by Aeromonas schubertii. The cumulative mortality within 40 days was 45%, and the diseased fish were 18 months old and 3545 cm in length. Multiple, ivory-white, firm nodules, 0.51 mm in diameter, were scattered throughout the kidney. Blood clots, 35 mm in diameter, were found in the liver. This is a disease frequently found in cultured snakehead throughout China. Isolated bacteria were Gram negative, facultatively anaerobic, motile, short rod-shaped, with a length of 0.31.0 mu m. Morphological and biochemical tests, as well as phylogenetic analysis derived from 16S rRNA, gyrB, rpoD and dnaJ gene sequencing all strongly indicated that these snakehead isolates are identical to A.similar to chubertii. In addition, the isolates possessed two plasmids: 5.0 kb and 10.0 kb. Antibiotic sensitivity testing of the isolates was carried out by the standard KirbyBauer disc diffusion method. Experimental infection assays were conducted, and pathogenicity (by intraperitoneal injection) was demonstrated in snakehead fingerlings and zebrafish, Brachydanio rerio (Hamilton)

Mixed mycobacterial infections in farmed sturgeons

Based on microbiological and histopathological examinations and DNA sequencing, several outbreaks of mycobacteriosis in the reared sturgeons, including Chinese sturgeon (Acipenser sinensis Gray) and Amur sturgeon (Acipenser schrencki), were identified during 2009 to 2010. Forty-nine isolates of non-tuberculous mycobacteria(NTM)were isolated from 19 diseased sturgeons. In total, seven species of Mycobacterium were identified, namely, Mycobacterium chelonae, Mycobacterium marinum, Mycobacterium gordonae, Mycobacterium fortuitum, Mycobacterium szulgai, Mycobacterium arupense and Mycobacterium porcinum. Among them, M. marinum was found to be more prevalent (89.5%) compared with the other mycobacterial species. When two molecular biological methods, PCR-DGGE (denaturing gradient gel electrophoresis) analysis and rpoB gene library sequencing, were used to analyse the mycobacterial DNAs extracted from the diseased fish tissues, mixed infections of two or three mycobacterial species were found being the predominant infection form (94.7%) in sturgeon mycobacteriosis. M. marinum was the only one species that caused sturgeon mycobacteriosis alone. Virulence assay showed that M. marinum possessed stronger pathogenicity to zebrafish killing 100% of fish in 28days at 10(3) cfu/fish than the other species. These results suggested that M. marinum is the major pathogenic bacteria in sturgeon mycobacteriosis. To the best of our knowledge, this study is the first report on mycobacteriosis in farmed Chinese and Amur sturgeons as well as the first isolation of M. porcinum and M. arupense from fish

Molecular characterization of Streptococcus agalactiae in diseased farmed tilapia in China

A severe outbreak of streptococcosis in cultured tilapia (Oreochromis niloticus) caused by Streptococcus agalactiae (Group B streptococcus, GBS) has occurred annually in Southern China during the past years, causing significant economic losses. Little is known about the genetic characteristics of the tilapia S. agalactiae that is prevalent in these areas. A total of 51 GBS isolates from tilapia were collected from 27 farms located in distinct geographic regions. The genetic characteristics of GBS were analyzed by MLST, MLVA, serotyping, and PCR screening of mobile genetic elements, genetic marker, and virulence-related genes. The results showed that all of S. agalactiae tilapia isolates have the genotype, Ia-ST7-bac-bca-fbsA-sip-cfb-IS1381-IS861-GBSil-ISSag2, which suggests a low level of genetic diversity and sharing of a recent and similar origin and a low level of genetic differentiation under similar environment selective pressures. Compared with the control, significant differences were detected between the tilapia strains and the S. agalactiae strains of human and bovine origin. Phage typing successfully differentiated all 51 tilapia GBS isolates into two distinct molecular types (type A and B). Interestingly, the phage type of the tilapia GBS isolates was also observed to shift from type A to type B, with the year 2010 as the turning point. Type B GBS isolates are currently prevalent in tilapia populations in China, and should thus be the target strains to detect and develop prophylactic-therapeutic measures. The genetic data obtained in the present study will be helpful in the determination of the epidemiology of tilapia streptococcosis internationally. (C) 2013 Elsevier B. V. All rights reserved.A severe outbreak of streptococcosis in cultured tilapia (Oreochromis niloticus) caused by Streptococcus agalactiae (Group B streptococcus, GBS) has occurred annually in Southern China during the past years, causing significant economic losses. Little is known about the genetic characteristics of the tilapia S. agalactiae that is prevalent in these areas. A total of 51 GBS isolates from tilapia were collected from 27 farms located in distinct geographic regions. The genetic characteristics of GBS were analyzed by MLST, MLVA, serotyping, and PCR screening of mobile genetic elements, genetic marker, and virulence-related genes. The results showed that all of S. agalactiae tilapia isolates have the genotype, Ia-ST7-bac-bca-fbsA-sip-cfb-IS1381-IS861-GBSil-ISSag2, which suggests a low level of genetic diversity and sharing of a recent and similar origin and a low level of genetic differentiation under similar environment selective pressures. Compared with the control, significant differences were detected between the tilapia strains and the S. agalactiae strains of human and bovine origin. Phage typing successfully differentiated all 51 tilapia GBS isolates into two distinct molecular types (type A and B). Interestingly, the phage type of the tilapia GBS isolates was also observed to shift from type A to type B, with the year 2010 as the turning point. Type B GBS isolates are currently prevalent in tilapia populations in China, and should thus be the target strains to detect and develop prophylactic-therapeutic measures. The genetic data obtained in the present study will be helpful in the determination of the epidemiology of tilapia streptococcosis internationally. (C) 2013 Elsevier B. V. All rights reserved

Bactericidal activity of grass carp Ctenopharyngodon idella C9-deficient serum against Aeromonas hydrophila

Neutralizing complement C9 in grass carp Ctenopharyngodon idella sera with rabbit anti-C9 sera against fish complement C9, demonstrated that bactericidal activity against Aeromonas hydrophila of the C9-deficient fish sera was greatly impaired. These results indicated that the fish complement C9 plays a key role in pathogen killing through the lytic pathway. (C) 2011 The Authors Journal of Fish Biology (C) 2011 The Fisheries Society of the British Isle

Effect of berberine hydrochloride on grass carp Ctenopharyngodon idella serum bactericidal activity against Edwardsiella ictaluri

Bactericidal activity of grass carp (Ctenopharyngodon idella) serum was significantly enhanced when pre-treated with 15 mg l(-1) or 3 mg l(-1) of berberine hydrochloride, an effective component of several commonly used herbal medicines in aquaculture. The complement consumption experiment demonstrated that berberine hydrochloride can certainly activate fish complement system. The results of both experiments suggested that berberine hydrochloride could enhance the serum bactericidal activity in grass carp by activating the complement system and indicating the potential in the prevention or treatment of fish diseases. (C) 2012 Elsevier Ltd. All rights reserved.Bactericidal activity of grass carp (Ctenopharyngodon idella) serum was significantly enhanced when pre-treated with 15 mg l(-1) or 3 mg l(-1) of berberine hydrochloride, an effective component of several commonly used herbal medicines in aquaculture. The complement consumption experiment demonstrated that berberine hydrochloride can certainly activate fish complement system. The results of both experiments suggested that berberine hydrochloride could enhance the serum bactericidal activity in grass carp by activating the complement system and indicating the potential in the prevention or treatment of fish diseases. (C) 2012 Elsevier Ltd. All rights reserved

Alterations of the gut microbiome of largemouth bronze gudgeon (Coreius guichenoti) suffering from furunculosis

High-throughput sequencing was applied to compare the intestinal microbiota in largemouth bronze gudgeon either healthy or affected by furunculosis. Proteobacteria, Actinobacteria, Tenericutes, Firmicutes and Bacteroidetes were detected as the predominant bacterial phyla in the gut of both diseased and healthy fish. The abundance of Proteobacteria differed significantly between the two groups of fish, mainly due to the overwhelming prevalence of Aeromonas in the diseased fish (81%+/- 17%), while the genus was unevenly spread among the apparently healthy fish (33%+/- 33%). The bacterial diversity in the intestine of diseased fish was markedly lower than in healthy fish. Analysis revealed the significant dissimilarity between the gut microbiota of diseased and healthy fish. The bacterial profiles in the gut were further characterized with the 28 phylotypes that were shared by the two groups. In diseased fish, two shared OTUs (OTU0001 and OTU0013) were closely related to Aeromonas salmonicida, their total proportion exceeding 70% of the sequences in diseased fish, while averaging 5.2%+/- 4.6% in the healthy fish. This result suggested the presence of healthy carriers of pathogenic A. salmonicida among the farmed fish, and the gut appeared as a probable infection source for furunculosis in largemouth bronze gudgeon