Colonization of Aeromonas salmonicida subsp. masoucida strains in Atlantic salmon (Salmo salar L.) during infection

Aeromonas salmonicida subsp. masoucida (ASM) is classified as atypical A. salmonicida and brought huge economic damages to the local salmonid aquaculture in China. An ASM strain named AS‐C4 was used to investigate the colonization of ASM in Atlantic salmon (Salmo salar L.) by an immersion challenge with the control group (T0, no AS‐C4), group T1 (2.67 × 10⁴ CFU/ml AS‐C4) and group T2 (2.67 × 10⁷ CFU/ml AS‐C4). The numbers of AS‐C4 copies in different fish tissues (gill, intestine, skin, blood, muscle, spleen, liver and kidney) were determined at different time points post challenge using the quantitative real‐time PCR (qRT‐PCR). AS‐C4 were detected in the gill and intestine as early as 0 hr after the challenge both in T1 and T2 groups, suggesting that the gill and intestine were probably the portals of entry of AS‐C4 into salmon. Although AS‐C4 could not be detected in the skin until 24 hr after the challenge in T1 group, it could be detected in the skin as early as 0 hr after the challenge in T2 group, indicating that the skin may also be a portal of entry of AS‐C4 into salmon. AS‐C4 was immediately detected in the blood within 3 hr after it entered the host, suggesting that AS‐C4 successfully invaded the bloodstream of fish. After AS‐C4 colonized the host, it colonized the internal tissues, such as the spleen, liver, kidney and muscle. The results of this study will contribute to the understanding of the pathogenesis of the ASM strains and give a broader understanding of the infection route of ASM in it's host, providing more information for the development of new therapeutic strategies to protect against this pathogen in aquaculture.     

Occurrence of Listonella anguillarum in seed production environments of Japanese flounder Paralichthys olivaceus (Temminck et Schlegel)

The present study was undertaken to investigate the distribution of Listonella anguillarum in the rearing water, fish and diets (rotifers) of Japanese flounder (Paralichthys olivaceus). A total of 793 isolates were obtained from the seed production environment of Japanese flounder and 175 out of them were identified as L. anguillarum by biochemical characterization, polymerase chain reaction (PCR) detection for VAH1 haemolysin gene and phylogenetic analysis of 16S ribosomal deoxyribonucleic acids (rDNA) sequences. These results strongly suggested that L. anguillarum is rapidly and accurately identified by the combination of incubation on thiosulphate–citrate–bile salt–sucrose agar at 35°C overnight and PCR detection for the VAH1 haemolysin gene. All flounder specimens and all rotifer samples harboured L. anguillarum at high densities of 6.9 × 10³–6.3 × 10⁵ colony forming units (CFU) g^?1 and 1.5 × 10⁴–2.3 × 10⁶ CFU g^?1, respectively, while as low as 5.0 × 10⁰–2.0 × 10¹ CFU mL^?1 of L. aguillarum were detected in only two of 11 seawater samples, even though no vibriosis occurred in larval and juvenile flounder of tanks. This fact strongly suggests that L. anguillarum is an inhabitant in the seed production environments of Japanese flounder.     

The Relationship Between Vaccine Dose and Efficacy in Channel Catfish Ictalurus punctatus Vaccinated as Fry with a Live Attenuated Strain of Edwardsiella ictaluri (RE‐33)1

Channel catfish Ictalurus punctatus were vaccinated at 12 d of age (post‐hatch) by a 2‐min bath immersion with attenuated Edwardsiella ictaluri RE‐33 at doses of 2.5 × 10⁵, 2.5 × 10⁶, and 2.4 × 10⁷ colony‐forming units CFU/mL of water. Following vaccination, RE‐33 was recovered from a greater percentage of fry that were vaccinated at the high and intermediate doses compared to fry vaccinated at the lowest dose. Independent of dose, the greatest percentage of RE‐33 positive fry occurred between 1 and 6 d post‐vaccination with a significant decrease in positive fry observed on day 12. A significant increase in mortality occurred 6 to 12 d post‐vaccination in fry vaccinated at the highest dose. No differences in post‐vaccination mortalities occurred between the other treatments. Following virulent E. ictaluri challenge, mortalities of fish vaccinated at doses of 2.5 × 10⁶ and 2.4 × 10⁷ CFU/mL were significantly less than those of fish vaccinated at 2.5 × 10⁵ CFU/mL and sham‐vaccinated control fish. These data show that vaccination with RE‐33 can offer protection against subsequent virulent E. ictaluri infection.     

Identification and Detection of the Pathogenic Bacteria Responsible for Swollen Abdomen Disease in Cultured Turbot,Scophthalmus maximus,and Flounder,Paralichthys olivaceus

Swollen abdomen disease (SAD) seriously threatens the aquaculture of turbots and flounders. Two dominant bacterial strains, FS1 and FS2, were isolated from the livers and kidneys of fish with diagnosed SAD. Applications of biochemical analyses, sequence analyses of 16S ribosomal RNA gene and heat shock protein 60 gene revealed two distinct pathogenic bacterial species, Edwardsiella tarda and Vibrio alginolyticus. These two hypothesized SAD‐causing pathogens were validated by challenge trials on flounder, Paralichthys olivaceus. Challenges with E. tarda and V. alginolyticus demonstrated lethal dose 50 (LD₅₀) values at 1.51 × 10⁵ colony‐forming units (CFU) and 1.05 × 10⁵ CFU, respectively. To develop a rapid SAD diagnosis method in flounders and turbots, a multiplex polymerase chain reaction (PCR) assay method was developed to simultaneously detect E. tarda and V. alginolyticus. Our multiplex PCR assay successfully detected as low as 10⁵ CFU/mL E. tarda and V. alginolyticus in flounders and turbots. No other common fish pathogens were detected with the multiplex PCR, suggesting a high specificity of this assay. The multiplex PCR assay developed in this study showed a great reliability in detecting SAD‐causing bacterial pathogens. Further optimization of this assay may contribute to the development of a novel SAD diagnosis tool in aquaculture.     

Development of a two‐step,non‐probed multiplex real‐time PCR for surveilling Vibrio anguillarum in seawater

Vibrio anguillarum is an aggressive and halophilic bacterial pathogen most commonly originating from seawater. Vibrio anguillarum presence in fisheries and aquaculture facilities causes significant morbidity and mortality among aquaculture species primarily from haemorrhaging of the body and skin of the infected fish that eventually leads to death, collectively recognized as the disease vibriosis. This study served to develop a non‐probe, multiplex real‐time PCR assay to rapidly detect V. anguillarum presence in seawater. Specific primers targeting genes vah1, empA and rpoN of V. anguillarum were selected for multiplex reaction among 11 different primer sets and the extension step was eliminated. Primer concentration, denaturation time as well as annealing time and temperature of DNA amplification were optimized, thus reducing reaction duration. The two‐step, non‐probed multiplex real‐time PCR set forth by this study detects as little as 3 CFU mL^?1 of V. anguillarum presence in sea water, without enrichment cultivation, in 70 min with molecular precision and includes melting curve confirmation.     

Interference of Listonella anguillarum with potential probiotic microorganisms isolated from farmed gilthead seabream (Sparus aurata, L.)

Four isolates obtained from gilthead seabream have been tested for their adhesion to the skin, gill and intestinal mucus of gilthead seabream, and for their ability to interfere with Listonella anguillarum, an important pathogen of farmed gilthead seabream. The ability to adhere to mucus was higher than 7% for all isolates. Three isolates showed an antagonistic effect against some of the pathogenic strains tested. They were assayed to interfere with the attachment of L. anguillarum to the mucus of gilthead seabream. Only two isolates significantly reduced the adhesion of L. anguillarum to all of the mucus assayed under exclusion, competition and displacement conditions. According to the criteria applied, the isolate Pdp11 was selected and its in vivo probiotic potential was assessed by oral administration followed by challenge with the pathogen L. anguillarum. For the feeding trial, a group of 50 gilthead seabreams received a commercial diet supplemented with lyophilized 10⁸ CFU g^?1 of this isolate for 15 days. An other group of similar characteristics received the non‐supplemented commercial diet. After the challenge, the mortality of the fish receiving the diet supplemented with the potential probiotic was significantly lower than that observed in the groups of fish receiving the non‐supplemented commercial diet.     

Diversity of siderophore‐producing bacteria isolated from the intestinal tracts of fish along the Japanese coast

This study examined the diversity of siderophore‐producing bacteria in the intestinal tracts of coastal fish in Japan and screened candidate bacterial strains for probiotic use in aquaculture. Of the 2637 bacteria isolated from the 27 fish specimens (13 species) and six environmental samples collected in this study, 266 isolates exhibited the ability to produce siderophores. Siderophore producers were detected in the intestines of 18 of the fish specimens caught (68%) at densities of 2.3 × 10⁴–2.3 × 10⁸ CFU g^?1, in all three seawater samples at 2.0 × 10²–1.3 × 10³ CFU mL^?1 and in all three sand samples at 2.6 × 10¹–2.8 × 10⁴ CFU g^?1. These findings suggest that siderophore‐producing bacteria are widely distributed in the intestinal tracts of coastal fish and their environments. Analysis of 16S rRNA gene sequences revealed that the siderophore producers belonged to 38 species, of which Vibrio splendidus, Vibrio ichthyoenteri and Vibrio crassostreae accounted for 32.7%, 19.5% and 11.3% of the 266 isolates, respectively, suggesting that these bacteria are indigenous to the intestinal tract of coastal fish. Six bacterial species, Enterovibri norvegicus, Photobacterium leiognathi, Photobacterium phosphoreum, Photobacterium rosenbergii, V. crassostrea and Vibrio scophthalmi were identified as possible candidates for use as probionts in fish aquaculture.     

Dietary probiotic Pediococcus acidilactici MA18/5M modulates the intestinal microbiota and stimulates intestinal immunity in rainbow trout (Oncorhynchus mykiss)

A study was conducted to evaluate the probiotic effect of Pediococcus acidilactici MA18/5M on rainbow trout, Oncorhynchus mykiss. Fish (310 ± 9 g) were fed a control diet or a P. acidilactici‐supplemented diet (at 2.4 × 10⁶ CFU/g) for 4 weeks. The probiotic was observed to populate the intestine with levels ranging from log 3.7 to 5.4 CFU/g. Furthermore, these populations were able to persist for at least 24 hr after the cessation of probiotic feeding. High‐throughput sequencing analysis of bacterial 16S rRNA libraries demonstrated that P. acidilactici was able to modulate the gut microbiome of rainbow trout and that the probiotic was detected as a common taxon on the mucosa and in the digesta of the probiotic fish (p < .05). Real‐time polymerase chain reaction demonstrated that feeding the probiotic upregulated pro‐inflammatory cytokines, interleukin‐1β, and interleukin‐8 and downregulated anti‐inflammatory interleukin‐10 compared to the control‐fed fish. Furthermore, the mRNA levels for the mucosal antibody immunoglobulin T was also elevated in probiotic‐fed fish. These findings help to explain some of the mechanisms behind the previously reported observed benefits of using this probiotic in the intestinal morphology and immunity of rainbow trout.     

Studies on bacterial pathogens isolated from diseased torafugu (Takifugu rubripes) cultured in marine industrial recirculation aquaculture system in Shandong Province,China

In spring of 2011, an epidemic outbreak of torafugu with high mortality occurred in an aquafarm with marine industrial recirculation aquaculture system (MIRAS) in Yantai, Shandong Province, China. The diseased fish showed anorexia, haemorrhaging and festering fin and skin and swelling internal organs. Forty‐five dominant bacterial isolates were obtained from the diseased fish, and were found to belong to 12 species according to 16S rRNA gene sequences. One strain from each species was selected to test the pathogenicity, and five strains were showed to be virulent to zebrafish. Whereas Enterovibrio nigricans Fr42 was highly virulent with the LD₅₀ of 7.8 × 10⁴ CFU g^?1, Photobacterium swingsii Fr23, Vibrio owensii Fr40, V. harveyi Fr51 and V. rotiferianus Fr71 were moderately virulent with the LD₅₀ of 1.7 × 10⁶ to 8.4 × 10⁶ CFU g^?1. Both the bacteria and their extracellular products of the five strains were found to show phospholipase, caseinase, gelatinase, amylase and/or lipase activities. The production of N‐acyl homoserine lactones (AHLs) of the five strains was detected by three different AHLs biosensors, and three of them were found to produce AHLs by at least one kind of biosensor. This is the first study describing various opportunistic bacterial pathogens of fish cultured in MIRAS in China.     

Comparison of Protective Efficacy between Formalin‐killed and aroA Gene‐knockout Vibrio anguillarum Vaccines in Olive Flounder,Paralichthys olivaceus

The aro genes in bacteria encode enzymes needed for the biosynthesis of aromatic amino acids, and mutant bacteria that are defective in the enzymes can replicate only a limited number in vertebrates owing to the lack or scarceness of chorismate, through which the mutant bacteria of the aro genes become attenuated. In the present study, the 5‐enolpyruvylshikimate‐3‐phosphate synthase (aroA) gene‐knockout Vibrio anguillarum (ΔaroA V. anguillarum) were generated by the allelic exchange method, and its vaccine potential was evaluated in the olive flounder, Paralichthys olivaceus, by comparing the protective efficacy of a formalin‐inactivated V. anguillarum. The LD₅₀ (50% lethal dose) value of ΔaroA V. anguillarum was 1000 times higher than that of wild‐type V. anguillarum in olive flounder fingerlings, and the growth of ΔaroA V. anguillarum was significantly suppressed by coincubation with nonimmune olive flounder serum compared with that of wild‐type V. anguillarum. The survival rates and serum agglutination titers of fish immunized with ΔaroA V. anguillarum were significantly higher than those of fish immunized with the same amount of formalin‐inactivated V. anguillarum, suggesting that although the inactivated V. anguillarum vaccine can provide a high protection in olive flounder, the protective efficacy can be enhanced by immunization with an auxotrophic mutant ΔaroA V. anguillarum.     

Effects on mortality and stress response in European sea bass, Dicentrarchus labrax (L.), fed mannan oligosaccharides (MOS) after Vibrio anguillarum exposure

The effects of dietary mannan oligosaccharides (MOS; 4 g kg^?1; Bio‐Mos, Alltech Inc, USA) in diets for European sea bass, Dicentrarchus labrax (L.), juveniles in relation to disease and stress resistance, combining intestinal infection with Vibrio anguillarum and stress challenge by confinement, were assessed in this study. After 8 weeks of MOS supplementation, fish were exposed to a pathogen challenge test against V. anguillarum by direct gut inoculation combined with a confinement stressor panel. Cumulative mortality of fish fed MOS caused by anally inoculated V. anguillarum decreased from 66% to 12.5% and from 54.1% to 25% in infected and infected + stressed fish, respectively, compared to fish fed control diet. Results for European sea bass revealed a positive effect of MOS dietary inclusion on disease resistance, in terms of cumulative mortality, against gut inoculated V. anguillarum, as well as reduced effects of stress on microbiota diversity. Both of these findings, together with the enhanced innate immune response and the higher gut mucus production and density of eosinophil granulocytes in gut mucosa obtained in previous studies after MOS supplementation ( Torrecillas et al. 2007, 2011a,b ) suggest that general reinforcement of the innate immune system, and particularly of the intestinal barrier efficiency, is the main defence mechanism of European sea bass fed MOS against pathogenic microorganisms.     

拟态弧菌的绿色荧光蛋白标记及其在感染草鱼体内的动态分布

为了示踪研究拟态弧菌感染草鱼的动态过程,将增强型绿色荧光蛋白编码基因EGFP克隆至质粒pBAD24,并转化到拟态弧菌04-14菌株构建荧光标记重组菌.重组菌经阿拉伯糖诱导后,能高效表达EGFP蛋白;荧光显微镜观察和流式细胞仪检测均发现重组菌能够发出明显的绿色荧光信号,且传至30代后质粒稳定率仍为100％;生物学特性检测结果显示,与野生株相比,重组菌的形态、生长特性和细胞黏附性均未发生明显改变.用标记重组菌浸泡感染草鱼,定点采集鳃、肠道、肌肉、头肾、脾脏和肝脏,借助荧光信号检测4d内细菌在不同组织脏器中的动态分布.结果发现感染4h后即可在肠道和鳃中检测到绿色荧光信号,标记菌检出量分别为3.60×108和2.36×106 CFU/g,直至10 h,其含量无明显变化,12 h后含菌量逐渐下降,但持续存在直至鱼死亡.标记菌在肌肉、头肾、脾脏和肝脏中呈现相似的动力学,感染24 h后才检测到荧光信号,24～ 85 h时间段含菌量呈现先增加后下降的变化,48 h达到峰值,检出量分别为9.58×104(肌肉)、8.75×104(头肾)、1.50×104(脾脏)和4.50×104 CFU/g(肝脏),但均低于肠道中的检出量,结果表明肠道是拟态弧菌黏附定植与繁殖的主要靶器官.     

Survival,persistence and proliferation of Vibrio anguillarum in juvenile turbot,Scophthalmus maximus (L.), intestine and faeces

The aim of this study was to determine whether orally administered V. anguillarum cells could survive passage through the intestinal tract of feeding turbot, and thereafter, proliferate in the released faeces. In addition, the growth of the pathogen in turbot faeces in the presence of a Carnobacterium sp. with inhibitory effects against a number of bacterial fish pathogens was studied. It was found that V. anguillarum cells survived the acidic environment of the stomach for several hours, persisted in the intestine and readily proliferated in the released faeces. The antagonistic Carnobacterium sp. inhibited the growth of V. anguillarum during co-culture in turbot faecal extracts. From the results, it was concluded that the turbot intestinal tract and faeces can serve as an enrichment site for V. anguillarum, and the use of intestinal bacteria with antagonistic activity against vibrios may be used to reduce the load of fish pathogenic vibrios in turbot hatcheries.     

Scanning Electron Microscopy of “Saddleback” Lesions Associated with Experimental Infections of Flavobacterium columnare in Channel Catfish,Ictalurus punctatus (Siluriformes: Ictaluridae), and Zebrafish,Danio rerio (Cypriniformes: Cyprinidae)

Laboratory‐reared, specific pathogen‐free fingerling channel catfish, Ictalurus punctatus, and adult zebrafish, Danio rerio, were each separately exposed by immersion challenge to the etiological agent of “columnaris disease,”Flavobacterium columnare (Japanese Collection of Microorganisms 21327 strain). At 24‐h post‐immersion, fish exhibiting a “saddleback” lesion were fixed whole in 10% neutral buffered formalin. Skin samples approximately 5 mm² were excised from both the margin and center of each saddleback lesion as well as from corresponding sites in control, non‐challenged, fish before being prepared routinely for scanning electron microscopy (SEM). Skin samples from control channel catfish and zebrafish had uniform, contiguous epidermal cells with continuous or closely apposed cell margins and well‐defined microridges. Channel catfish skin lesion samples had margins typified by epidermal sloughing and lesion centers that exhibited a multitude of rod‐shaped bacterial cells, approximately 3–10 µm long × 0.3–0.5 µm wide, intermingled with cellular debris across a surface characterized by denuded, strongly ridged, or folded dermal connective tissue. Zebrafish skin lesion samples had a multitude of rod‐shaped bacterial cells and exhibited comparable ultrastructural changes but some lacked scales. These findings are the first published SEM observations of columnaris disease and saddleback lesions in channel catfish and zebrafish and thereby advance our understanding of the ultrastructural characteristics of acute‐stage saddleback lesions and columnaris disease pathogenesis.     

Effect of Sublethal Hypoxia on the Immune Response and Susceptibility of Channel Catfish, Ictalurus punctatus, to Enteric Septicemia

The effect of sublethal hypoxia exposure on stress and immune responses and susceptibility to Edwardsiella ictaluri infection in juvenile channel catfish, Ictalurus punctatus, was investigated. Fish were monitored for temporal changes in glucose and cortisol concentrations before, during, and after 2 h exposure to sublethal hypoxia (<2 mg/L dissolved oxygen [DO]) and when maintained under normoxic conditions (6.0 ± 0.3 mg/L DO). Both blood glucose and plasma cortisol increased significantly in response to hypoxic conditions. Fish exposed to hypoxic or normoxic conditions were challenged with a high dose (1.3 × 10⁷ colony‐forming units [CFU]/mL) or a low dose (1.3 × 10⁵ CFU/mL) of E. ictaluri or sterile culture broth by 30‐min immersion bath. Approximately 1% of fish in both the normoxic and the hypoxic groups died when challenged with the low dose of E. ictaluri. However, when challenged with the high dose of E. ictaluri, catfish exposed to hypoxic conditions had significantly higher cumulative mortality (36 ± 12.1%) than those maintained under normoxic conditions (12 ± 1.1%). Total hemolytic complement and bactericidal activities and antibody response were lower in hypoxia‐exposed channel catfish, indicating that increased susceptibility of channel catfish to E. ictaluri may be the result of the immunosuppressive effects of the stress response to hypoxia.     

引起养殖许氏平鲉死亡的鳗利斯顿氏菌的分离鉴定及致病性

从患病许氏平鲉的病灶处分离得到一株优势菌,记为SS-1。通过两点背部肌肉注射进行人工感染实验,证明该菌对健康许氏平鲉的半数致死浓度为9.6×106CFU/mL,可感染许氏平鲉的多种内脏和组织。细菌形态学和生理生化特征测定结果显示,菌株SS-1为革兰氏阴性,短杆状,极生单鞭毛;氧化酶阳性、接触酶阳性、硝酸盐还原阳性、吲哚产生阳性、V-P试验阳性、精氨酸双水解酶阳性、H2S产生阴性等,与鳗利斯顿氏菌特征相符。16S rRNA基因序列分析结果表明,该菌与鳗利斯顿氏菌的同源性达到了99%,因此,将菌株SS-1鉴定为鳗利斯顿氏菌。     

Vibrio parahaemolyticus Associated with Mass Mortality of Postlarval Abalone,Haliotis diversicolor supertexta (L.), in Sanya,China

Outbreaks of mass mortality in postlarval abalone, Haliotis diversicolor supertexta (L.), have swept across south China since 2002 and in turn have resulted in many abalone farms closing. Twenty‐five representative bacterial isolates were isolated from a sample of five diseased postlarval abalone, taken 15 d postfertilization during an outbreak of postlarval disease in Sanya, Hainan Province, China in October 2004. A dominant isolate, referred to as Strain 6, was found to be highly virulent to postlarvae in an experimental challenge test, with a 50% lethal dose (LD₅₀) value of 3.2 × 10⁴ colony forming units (CFU)/mL, while six of the other isolates were weakly virulent with LD₅₀ values ranging from 1 × 10⁶ to 1 × 10⁷ CFU/mL, and the remaining 18 isolates were classified as avirulent with LD₅₀ values greater than 1 × 10⁸ CFU/mL. Using both an API 20E kit and 16S recombinant DNA sequence analysis, Strain 6 was shown to be Vibrio parahaemolyticus. It was sensitive to 4 and intermediately sensitive to 5 of the 16 antibiotics used when screening the antibiotic sensitivities of the bacterium. Extracellular products (ECPs) prepared from the bacterium were lethal to postlarvae when used in a toxicity test at a concentration of 3.77 mg protein/mL, and complete liquefaction of postlarvae tissues occurred within 24 h postexposure. Results from this study implicate V. parahaemolyticus as the pathogen involved in the disease outbreaks in postlarval abalone in Sanya and show that the ECPs may be involved in the pathogenesis of the disease.     

Effects of an Enterococcus faecium‐based probiotic on growth performance and health of Pirarucu,Arapaima gigas

Intensive fish farming has resulted in an increased concern for disease outbreaks. Probiotic use is one of the strategies being developed to improve fish health and productivity. Measures of probiotic colonization, growth performance, haematological characteristics and parasite load were used to evaluate the effect of diets supplemented with Enterococcus faecium on growth and health of Arapaima gigas juveniles. A completely randomized design with four treatments (diet with E. faecium at 1 × 10⁶ CFU/g and 1 × 10⁸ CFU/g, control diet and diet with the culture medium MRS) and three replicates was used. Ninety‐six Arapaima juveniles were distributed in 12 cages fed with the specified diet for 68 days. Colonization of the intestinal tract by lactic acid bacteria reduced the total number of heterotrophic bacteria in fish fed with probiotics compared to controls. Fish fed a supplemented diet containing 1 × 10⁸ CFU/g presented higher values of weight gain, survival and fish growth uniformity, and lower values of feed conversion ratio. The prevalence of Trichodina sp. could have affected the survival of fish in the control group. Reduction in parasite load and an increase in haematocrit, the number of erythrocytes, thrombocytes, neutrophils and monocytes were also observed in fish fed the diet containing 1 × 10⁸ CFU/g. Enterococcus faecium presented a probiotic effect in A. gigas juveniles and can be recommended for use at a concentration of 1 × 10⁸ CFU/g to modify the gut microbiota, improve growth performance and haematology and reduce parasitic load.     

Oxidative stress and antioxidant enzymes activities in the African catfish,Clarias gariepinus,experimentally challenged with Escherichia coli and Vibrio fischeri

The impacts of bacterial infection on cultivated fish species, African catfish, were investigated using oxidative stress biomarkers [lipid peroxidation (LPO) and protein carbonylation] and the activities of important antioxidant/detoxifying enzymes [catalase and glutathione S-transferase (GST)]. Fish were inoculated via oral gavage with one of the following treatments: 1 × 10⁵ CFU/ml of Escherichia coli (EC1), 2 × 10⁵ CFU/ml of E. coli (EC2), 1 × 10⁵ CFU/ml of Vibrio fischeri (V1), 2 × 10⁵ CFU/ml of V. fischeri (V2), gavaged with distilled water and not gavaged. Fish were maintained in the laboratory for 7 days after the bacterial inoculation, and the levels of LPO, protein carbonylation, GST, and catalase activities were determined in the muscle, gills, and liver of fish. Fish inoculated with bacteria (either E. coli or V. fischeri) had a significant higher levels of tissue LPO, protein carbonylation, and GST activities in a tissue-specific pattern (liver > muscle > gills). This appears to be related with the levels of bacterial inoculation, with effects more pronounced in fish inoculated with either EC2 or V2. The catalase activity did not differ significantly between the inoculated and fish that were not inoculated. The results of this study indicate that bacterial inoculation could result in oxidative stress in fish, and liver has a higher rate of oxidative stress per mg tissue compared to the gills and the muscle.