Dietary administration of the probiotic, Lactobacillus plantarum, enhanced the growth, innate immune responses, and disease resistance of the grouper Epinephelus coioides

The percent weight gain (PWG) and feed efficiency (FE) of Epinephelus coioides were calculated, and the lactobacilli and total microbiota in the posterior intestines, and non-specific immune parameters of grouper, and its susceptibility to Streptococcus sp. and an iridovirus were determined when the fish were fed diets containing Lactobacillus plantarum at 0 (control), 10(6), 10(8), or 10(10) colony-forming units (cfu) kg(-1) for 4 weeks. Results showed that grouper fed a diet containing L. plantarum at the levels of 10(6), 10(8), and 10(10) cfu kg(-1) had significantly increased PGW and FE especially at 10(8) cfu kg(-1) group which were 404.6% and 1.26, respectively. L. plantarum significantly increased in the fish posterior intestines during the L. plantarum feeding period, but decreased rapidly from the intestine within 1 week after changing to the control diet (without L. plantarum). Fish fed a diet containing L. plantarum at 10(6) and 10(8) cfu kg(-1) had significantly higher survival rates than those fed the control diet after challenge with Streptococcus sp., as well as those fed 10(8) cfu kg(-1) after challenge with an iridovirus, causing increases in the survival rates of 23.3%, 20.0%, and 36.7%, respectively, compared to the control group. The alternative complement activity (ACH(50)) level of fish fed diets containing L. plantarum after 4 weeks was significantly higher than that of fish fed the control diet, and that of the 10(8) cfu kg(-1) group was significantly higher than those of the 10(6) and 10(10) cfu kg(-1) groups, which increased by 83.4% compared to the control group. The lysozyme activity and glutathione peroxidase (GPx) activity of fish fed the L. plantarum-containing diets at 10(8) and 10(10) cfu kg(-1) significantly increased compared to those fed the 10(6) cfu kg(-1)L. plantarum diet and control diet, and had increased by 76.3% and 136.6%, and 57.1% and 113.3%, respectively, compared to those fed the control diet. The phagocytic activity (PA), phagocytic index (PI), and respiratory bursts of head kidney leucocytes of fish fed 10(6), 10(8), and 10(10) cfu kg(-1)L. plantarum diets were significantly higher than those of fish fed the control diet after 4 weeks of feeding, and increased 2.2-, 2.2-, and 2.3-fold; 1.8-, 1.8-, and 2.0-fold; and 1.4-, 1.4-, and 1.4-fold, respectively, compared to the control group. We therefore recommend dietary L. plantarum administration at 10(8) cfu kg(-1) to promote growth and enhance immunity and resistance against Streptococcus sp. and an iridovirus of E. coioides.

Rapid separation and concentration of food-borne pathogens in food samples prior to quantification by viable-cell counting and real-time PCR

Buoyant density gradient centrifugation has been used to separate bacteria from complex food matrices, as well as to remove compounds that inhibit rapid detection methods, such as PCR, and to prevent false-positive results due to DNA originating from dead cells. Applying a principle of buoyant density gradient centrifugation, we developed a method for rapid separation and concentration following filtration and low- and high-speed centrifugation, as well as flotation and sedimentation buoyant density centrifugation, for 12 food-borne pathogens (Salmonella enterica, Escherichia coli, Yersinia enterocolitica, Campylobacter jejuni, Vibrio cholerae O139, Vibrio parahaemolyticus O3K6, Vibrio vulnificus, Providencia alcalifaciens, Aeromonas hydrophila, Bacillus cereus, Staphylococcus aureus, and Clostridium perfringens) in 13 different food homogenates. This method can be used prior to real-time quantitative PCR (RTi-qPCR) and viable-cell counting. Using this combined method, the target organisms in the food samples theoretically could be concentrated 250-fold and detected at cell concentrations as low as 10(1) to 10(3) CFU/g using the RTi-qPCR assay, and amounts as small as 10(0) to 10(1) CFU/g could be isolated using plate counting. The combined separation and concentration methods and RTi-qPCR confirmed within 3 h the presence of 10(1) to 10(2) CFU/g of Salmonella and C. jejuni directly in naturally contaminated chicken and the presence of S. aureus directly in remaining food items in a poisoning outbreak. These results illustrated the feasibility of using these assays for rapid inspection of bacterial food contamination during a real-world outbreak.

Pathogenicity of Vibrio alginolyticus for cultured gilt-head sea bream (Sparus aurata L.)

The in vivo and in vitro pathogenic activities of whole cells and extracellular products of Vibrio alginolyticus for cultured gilt-head sea bream were evaluated. The 50% lethal doses ranged from 5.4 x 10(4) to 1.0 x 10(6) CFU/g of body weight. The strains examined had the ability to adhere to skin, gill, and intestinal mucus of sea bream and to cultured cells of a chinook salmon embryo cell line. In addition, the in vitro ability of V. alginolyticus to adhere to mucus and skin cells of sea bream was demonstrated by scanning electron microscopy. The biological activities of extracellular products of V. alginolyticus were hydrolytic activities; the products were able to degrade sea bream mucus. V. alginolyticus was cytotoxic for fish cell lines and lethal for sea bream. Moreover, the extracellular products could degrade sea bream tissues. However, experiments performed with the bath immersion inoculation technique demonstrated that V. alginolyticus should be considered a pathogen for sea bream only when the mucus layer is removed and the skin is damaged.

Inhibition of Vibrio biofilm formation by a marine actinomycete strain A66

China remains by far the largest aquaculture producer in the world. However, biofilms formed by pathogenic Vibrio strains pose serious problems to marine aquaculture. To provide a strategy for biofilm prevention, control, and eradication, extracts from 88 marine actinomycetes were screened. Thirty-five inhibited the biofilm formation of Vibrio harveyi, Vibrio vulnificus, and Vibrio anguillarum at a concentration of 2.5% (v/v). Thirty-three of the actinomycete extracts dispersed the mature biofilm. Six extracts inhibited the quorum-sensing system of V. harveyi by attenuating the signal molecules N-acylated homoserine lactones' activity. Strain A66, which was identified as Streptomyces albus, both attenuated the biofilms and inhibited their quorum-sensing system. It is suggested that strain A66 is a promising candidate to be used in future marine aquaculture.

Dietary administration of the probiotic, Bacillus subtilis E20, enhances the growth, innate immune responses, and disease resistance of the grouper, Epinephelus coioides

The aim of this study was to improve the growth performance, immune response and disease resistance of grouper, Epinephelus coioides by using probiotic, Bacillus subtilis E20. The percent weight gain (PWG) and feeding efficiency (FE) of grouper administered the probiotic B. subtilis E20 were calculated. Survival of B. subtilis E20 in the posterior intestines was determined using a specific primer pair of BPHYF/BPHYR, as were the non-specific immune parameters of grouper, and its susceptibility to Streptococcus sp. and an iridovirus when fish were fed diets containing B. subtilis at 0 (control), 10(4), 10(6), and 10(8) colony-forming units (cfu) g(-1) up to 28 days. Results showed that grouper fed a diet containing B. subtilis at the levels of 10(4), 10(6), and 10(8) cfu g(-1) had significantly increased PGW (203.0%, 229.6%, and 238.0%) and FE (1.15, 1.20, and 1.22) compared to control (191.8% and 1.0), and these directly increased in a dose-dependent manner with B. subtilis concentrations. B. subtilis was able to survive in the fish's posterior intestines during the feeding period. The survival rate increased in grouper challenged with Streptococcus sp. or an iridovirus when the fish were fed B. subtilis at 10(4), 10(6), and 10(8) cfu g(-1) for 14 and 28 days, and it was higher at 28 days than at 14 days. After 28 days of feeding, the relative survival percentages of fish challenged with Streptococcus sp. and an iridovirus were 22.8, 40.9 and 45.5, and 21.7, 30.4, and 52.2, respectively. The phagocytic activity, respiratory bursts, and superoxide dismutase (SOD) level of head kidney leucocytes as well as serum lysozyme activity and serum alternative complement activity (ACH(50)) of fish fed diets containing B. subtilis at 10(4), 10(6) and 10(8) cfu g(-1) were significantly and dose-dependently higher than those of fish fed the control diet for 28 days. We therefore recommend dietary B. subtilis E20 administration of 10(4) - 10(8) cfu g(-1) to E. coioides to promote growth, and enhance immunity and resistance against Streptococcus sp. and an iridovirus. The best results were seen in the 10(8) cfu g(-1) group fed for 28 days.

Characterization of Pseudomonas spp. associated with spoilage of gilt-head sea bream stored under various conditions

The population dynamics of pseudomonads in gilt-head sea bream Mediterranean fish (Sparus aurata) stored under different conditions were studied. Phenotypic analysis and sodium dodecyl sulfate-polyacrylamide gel electrophoresis of whole-cell proteins were performed to identify a total of 106 Pseudomonas strains isolated from S. aurata stored under different temperatures (at 0, 10, and 20 degrees C) and packaging conditions (air and a modified atmosphere of 40% CO(2)-30% N(2)-30% O(2)). Pseudomonas lundensis was the predominant species, followed by Pseudomonas fluorescens, while Pseudomonas fragi and Pseudomonas putida were detected less frequently. Fluorescent Pseudomonas strains dominated under air conditions, while proteolytic and less lipolytic strains dominated under modified-atmosphere packaging. Different storage conditions appear to govern the selection of pseudomonads in gilt-head sea bream fish.

Epidermal 'alarm substance' cells of fishes maintained by non-alarm functions: possible defence against pathogens, parasites and UVB radiation

Many fishes possess specialized epidermal cells that are ruptured by the teeth of predators, thus reliably indicating the presence of an actively foraging predator. Understanding the evolution of these cells has intrigued evolutionary ecologists because the release of these alarm chemicals is not voluntary. Here, we show that predation pressure does not influence alarm cell production in fishes. Alarm cell production is stimulated by exposure to skin-penetrating pathogens (water moulds: Saprolegnia ferax and Saprolegnia parasitica), skin-penetrating parasites (larval trematodes: Teleorchis sp. and Uvulifer sp.) and correlated with exposure to UV radiation. Suppression of the immune system with environmentally relevant levels of Cd inhibits alarm cell production of fishes challenged with Saprolegnia. These data are the first evidence that alarm substance cells have an immune function against ubiquitous environmental challenges to epidermal integrity. Our results indicate that these specialized cells arose and are maintained by natural selection owing to selfish benefits unrelated to predator-prey interactions. Cell contents released when these cells are damaged in predator attacks have secondarily acquired an ecological role as alarm cues because selection favours receivers to detect and respond adaptively to public information about predation.

Dominance of Mycoplasma in the guts of the Long-Jawed Mudsucker, Gillichthys mirabilis, from five California salt marshes

We analysed the gut microflora of the Long-Jawed Mudsucker, Gillichthys mirabilis by polymerase chain reaction/denaturing gradient gel electrophoresis and cloning and sequencing 16S rRNA gene amplicons. Fish were collected at five sites in northern and southern California, USA. The gut microflora assemblages of all G. mirabilis were similar, very simple and dominated by one or more Mycoplasma ribotypes. Hindguts were dominated by Mycoplasmas that were most similar to a ribotype retrieved from Atlantic salmon guts. A Mycoplasma ribotype that was 95% similar to Mycoplasma mobile was the dominant in the foregut.

Applicability of an Arrhenius model for the combined effect of temperature and CO(2) packaging on the spoilage microflora of fish

The temperature behavior of the natural microflora on the Mediterranean fish red mullet (Mullus barbatus) was examined as a case study. The growth of the spoilage bacteria Pseudomonas spp., Shewanella putrefaciens, Brochothrix thermosphacta, and lactic acid bacteria was modeled as a function of temperature and the concentration of carbon dioxide in modified atmosphere packaging. Combined models were developed and comparatively assessed based on polynomial, Belehradek, and Arrhenius equations. The activation energy parameter of the Arrhenius model, E(A), was independent of the packaging atmosphere and ranged from 75 to 85 kJ/mol for the different bacteria, whereas the preexponential constant decreased exponentially with the packaging CO(2) concentration. We evaluated the applicability of the models developed by using experimental bacterial growth rates obtained from 42 independent experiments performed with three Mediterranean fish species and growth rates predicted from the models under the same temperature and packaging conditions. The accuracy factor and bias factor were used as statistical tools for evaluation, and the developed Arrhenius model and the Belehradek model were judged satisfactory overall.

Association of marine archaea with the digestive tracts of two marine fish species

Recent studies have shown that archaea which were always thought to live under strict anoxic or extreme environmental conditions are also present in cold, oxygenated seawater, soils, the digestive tract of a holothurian deep-sea-deposit feeder, and a marine sponge. In this study, we show, by using PCR-mediated screening in other marine eukaryotes, that marine archaea are also present in the digestive tracts of flounder and grey mullet, two fish species common in the North Sea, in fecal samples of flounder, and in suspended particulate matter of the North Sea water column. No marine archaea could be detected in the digestive tracts of mussels or the fecal pellets of a copepod species. The archaeal 16S ribosomal DNA clone libraries of feces of flounder and the contents of the digestive tracts of grey mullet and flounder were dominated by group II marine archaea. The marine archaeal clones derived from flounder and grey mullet digestive tracts and feces formed a distinct cluster within the group II marine archaea, with 76.7 to 89. 8% similarity to previously described group II clones. Fingerprinting of the archaeal community of flounder digestive tract contents and feces by terminal restriction fragment length polymorphism of archaeal 16S rRNA genes after restriction with HhaI showed a dominant fragment at 249 bp, which is likely to be derived from group II marine archaea. Clones of marine archaea that were closely related to the fish-associated marine archaea clones were obtained from suspended particulate matter of the water column at two stations in the North Sea. Terminal restriction fragment length polymorphism fingerprinting of the archaeal community present in suspended particulate matter showed the same fragment pattern as was found for the archaeal community of the flounder digestive tract contents and feces. These data demonstrate that marine archaea are present in the digestive tracts and feces of very common marine fish. It is possible that the marine archaea associated with the digestive tracts of marine fish are liberated into the water column through the feces and subsequently contribute to the marine archaeal community of suspended particulate matter.

Identification and characterization of putative virulence genes and gene clusters in Aeromonas hydrophila PPD134/91

Aeromonas hydrophila is a gram-negative opportunistic pathogen of animals and humans. The pathogenesis of A. hydrophila is multifactorial. Genomic subtraction and markers of genomic islands (GIs) were used to identify putative virulence genes in A. hydrophila PPD134/91. Two rounds of genomic subtraction led to the identification of 22 unique DNA fragments encoding 19 putative virulence factors and seven new open reading frames, which are commonly present in the eight virulence strains examined. In addition, four GIs were found, including O-antigen, capsule, phage-associated, and type III secretion system (TTSS) gene clusters. These putative virulence genes and gene clusters were positioned on a physical map of A. hydrophila PPD134/91 to determine their genetic organization in this bacterium. Further in vivo study of insertion and deletion mutants showed that the TTSS may be one of the important virulence factors in A. hydrophila pathogenesis. Furthermore, deletions of multiple virulence factors such as S-layer, serine protease, and metalloprotease also increased the 50% lethal dose to the same level as the TTSS mutation (about 1 log) in a blue gourami infection model. This observation sheds light on the multifactorial and concerted nature of pathogenicity in A. hydrophila. The large number of putative virulence genes identified in this study will form the basis for further investigation of this emerging pathogen and help to develop effective vaccines, diagnostics, and novel therapeutics.

Identification and functional characterization of an interferon regulatory factor 7-like (IRF7-like) gene from orange-spotted grouper, Epinephelus coioides

Interferon regulatory factor (IRF) 7 plays a crucial role in modulating cellular responses to viral infection and cytokines, including interferons (IFNs). In the present study, a novel IRF7 gene (designated as EcIRF7) was cloned and characterized from orange-spotted grouper, Epinephelus coioides. The full-length EcIRF7 cDNA is composed of 2089 bp and encodes a polypeptide of 433 amino acids with 81% identity to IRF7 of Siniperca chuatsi, and the genomic DNA of EcIRF7 consists of 9 exons and 8 introns, with a length of approximately 5629 bp. EcIRF7 contains three conserved domains including a DNA-binding domain (DBD), an IRF associated domain (IAD) and a serine-rich domain, all of which are highly conserved across species. Recombinant EcIRF7 was expressed in Escherichia coli BL21 (DE3) and purified for mouse anti-EcIRF7 serum preparation. Realtime quantitative PCR (RT-qPCR) analysis revealed a broad expression of EcIRF7, with a relative strong expression in spleen, kidney, skin and intestine. The expression of EcIRF7 was differentially up-regulated after stimulation with Vibrio vulnificus, Staphylococcus aureus and Singapore grouper iridovirus (SGIV). EcIRF7 showed similar intracellular localization pattern to those of mammalian and chicken, and translocated into nucleus after SGIV infection. Further more, EcIRF7 was proved to be capable of activating zebrafish type I IFN promoter and inhibiting the replication of SGIV in grouper spleen (GS) cells. These results suggest that EcIRF7 is potentially involved in grouper immune responses to invasion of viral and bacterial pathogens.

Biogenic amines and sensory changes associated with the microbial flora of Mediterranean gilt-head sea bream (Sparus aurata) stored aerobically at 0, 8, and 15 degrees C

Changes in the concentrations of tyramine, agmatine, putrescine, cadaverine, spermidine, tryptamine, spermine, histamine, and trimethylamine were studied in parallel with the development of the microbial population during the storage of Mediterranean gilt-head sea bream (Sparus aurata) at three temperatures (0, 8, 15 degrees C). Changes in sensory scores were also recorded. Pseudomonads and H2S-producing bacteria were the dominant microorganisms. Enterobacteriaceae and lactic acid bacteria were also present in the fish microflora. Among the biogenic amines, putrescine and cadaverine were detected when pseudomonads exceeded 10(6) to 10(7) CFU/g. Histamine was produced only in samples stored at 15 degrees C. Tyramine, tryptamine, agmatine, and trimethylamine were absent regardless of the storage temperature.

Identification and characterization of extracellular cyclic dipeptides as quorum-sensing signal molecules from Shewanella baltica, the specific spoilage organism of Pseudosciaena crocea during 4 °C storage

Quorum-sensing (QS) signaling molecules are able to mediate specific gene expression inside spoilage bacteria in response to population density and thus are implicated in food spoilage. In the present work, a total of 102 strains of spoilage bacteria were isolated from Pseudosciaena crocea at 4 °C storage, and of these, 60 strains were identified as Shewanella spp., and 48 strains (47.1%) were identified as S. baltica. In addition, the spoilage capabilities of three different S. baltica strains (00A, 00B, and 00C) were compared by total volatile base nitrogen (TVB-N) and sensory analysis (off-odors). Furthermore, four cyclic dipeptides (diketopiperazines, DKPs) that function as QS signal molecules were isolated and characterized from the extracellular metabolites of S. baltica 00C which had the strongest spoilage activity based on gas chromatography mass spectrometry (GC-MS). By supplementation of four synthesized DKPs, the spoilage capability of S. baltica could be significantly enhanced. So far, this was the first attempt to characterize DKPs as the signaling molecules in QS of S. baltica. Our study may provide some evidence of the role of DKPs involved in microbial spoilage.

Probiotics as an environment-friendly approach to enhance red sea bream, Pagrus major growth, immune response and oxidative status

A usual strategy in modern aquaculture to combat production bottlenecks associated with intensification is preventive health care through the use of consumer and environment-friendly alternatives including probiotics. The current study evaluates the influence of Lactobacillus rhamnosus (LR), a lyophilized probiotic bacterium, on health status and performance of red sea bream (Pagrus major). Probiotics were incorporated in the diets at four different concentrations: 0 (control diet, LR0), 10(2) (LR1), 10(4) (LR2) and 10(6) (LR3) cells g(-1) and diets were administered to the fish for a period of 8 weeks. After the feeding trial, final body weight, body weight gain, specific growth rate, protease activity, protein digestibility, Lactobacillus sp. intestinal count, and superoxide dismutase were significantly higher in all probiotic-fed groups (P < 0.05). In addition, lipid and dry matter digestibility, reactive oxygen metabolites, biological antioxidant potential, and humoral and mucosal immune parameters including (total serum protein, alternative complement pathway, bactericidal and peroxidase activities) were also significantly elevated in fish fed probiotic supplementations being the effects dose-dependent. All growth, feed utilization, immune and oxidative parameters were significantly improved following probiotic administration. Present results revealed that L. rhamnosus is a promising probiotic candidate employed to help red sea bream protect themselves, thus promoting safe farming that would be less dependent on chemotherapy against infectious diseases.

Mycobacteriosis in cultured striped bass from California

Striped bass (Morone saxatilis) juveniles raised in an intensive culture system had chronic mortality resulting from infections with Mycobacterium marinum. Approximately one-half of a population of 900 yearlings succumbed to the disease and 80% of those remaining were infected. The bacteria were isolated on Petrignani's medium after 7 days at 25 C and subcultures grew at temperatures from 20 to 37 C. The disease was characterized by systemic nodular lesions in all major organs. Older tubercles contained numerous acid-fast bacilli. Chemotherapy by feeding rifampin (6 mg/100 g of food for 60 days) was not an effective treatment. Subclinical mycobacteriosis in adult striped bass may be the source for vertical transmission to their progeny.

Molecular characterization of "Candidatus Parilichlamydia carangidicola," a novel Chlamydia-like epitheliocystis agent in yellowtail kingfish, Seriola lalandi (Valenciennes), and the proposal of a new family, "Candidatus Parilichlamydiaceae" fam. nov. (order Chlamydiales)

Three cohorts of farmed yellowtail kingfish (Seriola lalandi) from South Australia were examined for Chlamydia-like organisms associated with epitheliocystis. To characterize the bacteria, 38 gill samples were processed for histopathology, electron microscopy, and 16S rRNA amplification, sequencing, and phylogenetic analysis. Microscopically, the presence of membrane-enclosed cysts was observed within the gill lamellae. Also observed was hyperplasia of the epithelial cells with cytoplasmic vacuolization and fusion of the gill lamellae. Transmission electron microscopy revealed morphological features of the reticulate and intermediate bodies typical of members of the order Chlamydiales. A novel 1,393-bp 16S chlamydial rRNA sequence was amplified from gill DNA extracted from fish in all cohorts over a 3-year period that corresponded to the 16S rRNA sequence amplified directly from laser-dissected cysts. This sequence was only 87% similar to the reported "Candidatus Piscichlamydia salmonis" (AY462244) from Atlantic salmon and Arctic charr. Phylogenetic analysis of this sequence against 35 Chlamydia and Chlamydia-like bacteria revealed that this novel bacterium belongs to an undescribed family lineage in the order Chlamydiales. Based on these observations, we propose this bacterium of yellowtail kingfish be known as "Candidatus Parilichlamydia carangidicola" and that the new family be known as "Candidatus Parilichlamydiaceae."

Sensorial and microbial effects of gaseous ozone on fresh scad (Trachurus trachurus)

The bactericidal activity of gaseous ozone was investigated using a commercial ozone generator. Five species of fish bacteria, Pseudomonas putida, Shewanella putrefaciens, Brochothrix thermosphacta, Enterobacter sp. and Lactobacillus plantarum, were inoculated on agar surfaces and exposed to different ozonation times in a gas chamber. Results showed ozone in relatively low concentrations (< 0.27 x 10(-3) g l-1) was an effective bactericide of vegetative cells of the five fish bacteria. The age of the cell culture was shown to influence the cell response following exposure. Survival rate was not linearly related to ozonation time, but exhibited biphasic death over an extended period. Similar bactericidal effects were observed on fish skin treated with ozone daily in the laboratory, with decreases of 1.0 log cfu cm-2 for the micro-organisms studied. Whole fish treated daily in the laboratory using a commercial ozone generator showed improved scores for sensory analyses compared with the controls. The results were statistically significant. Fish treated on board ships were also analysed for microbiological and sensory changes. Controls were obtained from a similar vessel without the ozone facility in the hold. Similar trends to those recorded in the laboratory for the microbiological and sensory results on ozonated fish were observed.

Kinetics of adhesion of selected fish-pathogenic Vibrio strains of skin mucus of gilt-head sea bream (Sparus aurata L.)

The kinetics of adhesion of Vibrio strains isolated from diseased fish to skin mucus of gilt-head sea bream was studied. A modified Langmuir adsorption isotherm was calculated, and the results obtained indicate that the strains tested (Vibrio alginolyticus DP1HE4 and Vibrio anguillarum-like DC12R8 and DC12R9) showed a saturation kinetics except for V. alginolyticus (CAN), which showed a proportional adsorption kinetics. The adhesive capability for skin mucus does not seem to be an essential virulence factor of pathogenic strains of Vibrio, since this specific interaction depended on several environmental factors, temperature and salinity being the most important. However, the absence of an inhibitory effect of mucus on the pathogenic microorganisms, and the capability of the Vibrio strains to utilize mucus as a carbon source, could favor their settlement on the skin with a potential for infection of cultured, stressed fish.

Effect of cold plasma on maintaining the quality of chub mackerel (Scomber japonicus): biochemical and sensory attributes

BACKGROUND

Atmospheric cold plasma (ACP) has emerged as a potential alternative to traditional methods for non-thermal food decontamination. However, few data are available about ACP treatment for seafood. In this study, dielectric barrier discharge (DBD) was applied to generate CP, and the aim of the study was to investigate the effectiveness of DBD-ACP on improving the quality of chub mackerel on the basis of chemical, microbial and sensory characteristics.

RESULTS

The effect of DBD-ACP on the quality of chub mackerel (Scomber japonicus) during storage was examined. Results revealed that the optimal voltage level and exposure time of this treatment were 60 kV and 60 s respectively, and such conditions exhibited excellent inactivation efficacy and weak influence on proximate chemical compositions. Variations in total viable count (TVC), sensory scores and total volatile basic nitrogen (TVB-N) indicated that ACP treatment extended the shelf life of chub mackerel to 14 days, whereas samples without this treatment exceeded the limits of the three parameters after 6 days. The slow development rates of peroxide value (PV) and thiobarbituric acid (TBA) value implied that lipid oxidation was also effectively retarded by ACP exposure. Scanning electron microscopy confirmed that CP could effectively delay the degradation of myofibrillar proteins and enhance the stability of tissue structures.

CONCLUSION

The excellent antimicrobial efficacy of ACP treatment makes it a potential and promising alternative to other seafood preservation technology. This is the first report on the application of ACP to seafood, which is essential to perishable food storage. © 2018 Society of Chemical Industry.

Portal of entry for pathogenic Vibrio alginolyticus into large yellow croaker Pseudosciaena crocea, and characteristics of bacterial adhesion to mucus

The portal of entry for pathogenic Vibrio alginolyticus into large yellow croaker Pseudosciaena crocea is via the intestinal tract rather than gill or skin according to the kinetics of the bacterial adhesion to different mucus. The different effects on adhesion caused by proteolytic enzymes and heat treatment might be due to the different chemical compositions of mucus. Adhesion of V. alginolyticus to mucus depends on concerted action of bacterial surface structures such as cell-surface proteins, somatic antigens, flagella, etc. In addition, starvation and monosaccharides, especially fructose, inhibit the bacterial adhesion to the mucus. Knowledge of these adhesive characteristics should be very useful for designing more efficacious prophylactic strategies.

Extended serotyping scheme for Vibrio anguillarum with the definition and characterization of seven provisional O-serogroups

The present paper summarizes the serotyping scheme of the fish pathogenic bacterium Vibrio anguillarum and defines seven additional O-serogroups. Strains, collected in our laboratories that were nontypable with antisera against the previously defined 16 O-serotypes, were used for generating new antisera and were characterized further by means of LPS profiles, Western blots, and serological reactions. On the basis of the results, it is suggested that the seven new O-serogroups are to be included in the existing serotyping system as serotypes O17-O23. However, the existence of further V. anguillarum strains that were not typable with any of the 23 O-antisera suggested the existence of additional O-serotypes within this species. The relevance of the description of additional O-serotypes for the species V. anguillarum is discussed.

Effects of temperature change on the innate cellular and humoral immune responses of orange-spotted grouper Epinephelus coioides and its susceptibility to Vibrio alginolyticus

Orange-spotted grouper Epinephelus coioides held at 27 degrees C were then further cultured at 19, 27 (control), and 35 degrees C, and were examined for innate cellular and humoral responses after 3-96 h. The total leucocyte count, respiratory burst, and phagocytic activity significantly decreased 3, 48, and 96 h after fish were transferred to 19 and 35 degrees C. Both the alternative complement pathway (ACH(50)) and the lysozyme activity significantly decreased at 3-96 h after fish were transferred to 19 and 35 degrees C. In another experiment, groupers reared at 27 degrees C at 34 per thousand salinity were injected with Vibrio alginolyticus grown in tryptic soy broth (TSB) at a dose of 2.3 x 10(9) colony-forming units (cfu) fish(-1), and then further reared in water temperatures of 19, 27 (control), and 35 degrees C. The cumulative mortalities of V. alginolyticus-injected fish held in 19 and 35 degrees C were significantly higher than that of injected fish held in 27 degrees C. Resistance had decreased after 12 h for the challenged grouper held at 35 degrees C. All injected fish held in 19 degrees C had died after 72 h. It was concluded that at 12 h after transfer of grouper from 27 to 19 and 35 degrees C, immunity was suppressed and resistance against V. alginolyticus had decreased.

Fish lily type lectin-1 contains β-prism architecture: immunological characterization

In this study we report a full-length lily type lectin-1 (CsLTL-1) identified from striped murrel, Channa striatus. CsLTL-1 was identified from the established C. striatus cDNA library using GS-FLX™ genome sequencing technology and was found to contain 354 nucleotide base pairs and its open reading frame (ORF) encodes a 118 amino acid residue. CsLTL-1 mRNA is predominately expressed in the gills and is up-regulated upon infection with fungus (Aphanomyces invadans) and bacteria (Aeromonas hydrophila). Hemagglutination studies with recombinant CsLTL-1 show that, at 4μg/ml agglutinates occurs in a calcium independent manner and is inhibited in the presence of d-mannose (50mM) and d-glucose (100mM). The CsLTL-1 sequence was completely characterized using various bioinformatics tools. CsLTL-1 peptide contains a mannose binding site at 30-99 along with its specific motif of β-prism architecture. The phylogenetic analysis showed that CsLTL-1 clustered together with LTL-1 from Oplegnathus fasciatus. CsLTL-1 protein 3D structure was predicted by I-Tasser program and the model was evaluated using Ramachanran plot analysis. The secondary structure analysis of CsLTL-1 reveals that the protein contains 23% β-sheets and 77% coils. The overall results showed that CsLTL-1 is an important immune gene involved in the recognition and elimination of pathogens in murrels.

Molecular evidence for association of chlamydiales bacteria with epitheliocystis in leafy seadragon (Phycodurus eques), silver perch (Bidyanus bidyanus), and barramundi (Lates calcarifer)

Epitheliocystis in leafy seadragon (Phycodurus eques), silver perch (Bidyanus bidyanus), and barramundi (Lates calcarifer), previously associated with chlamydial bacterial infection using ultrastructural analysis, was further investigated by using molecular and immunocytochemical methods. Morphologically, all three species showed epitheliocystis cysts in the gills, and barramundi also showed lymphocystis cysts in the skin. From gill cysts of all three species and from skin cysts of barramundi 16S rRNA gene fragments were amplified by PCR and sequenced, which clustered by phylogenetic analysis together with other chlamydia-like organisms in the order Chlamydiales in a lineage separate from the family Chlamydiaceae. By using in situ RNA hybridization, 16S rRNA Chlamydiales-specific sequences were detected in gill cysts of silver perch and in gill and skin cysts of barramundi. By applying immunocytochemistry, chlamydial antigens (lipopolysaccharide and/or membrane protein) were detected in gill cysts of leafy seadragon and in gill and skin cysts of barramundi, but not in gill cysts of silver perch. In conclusion, this is the first time epitheliocystis agents of leafy seadragon, silver perch and barramundi have been undoubtedly identified as belonging to bacteria of the order Chlamydiales by molecular methods. In addition, the results suggested that lymphocystis cysts, known to be caused by iridovirus infection, could be coinfected with the epitheliocystis agent.