Quantitative and qualitative analyses of the bacterial microbiota of tilapia (Oreochromis niloticus) cultured in earthen ponds in the Philippines

Preparation of valine-curcumin conjugate and its in vitro antibacterial and antitumor activity and in vivo biological effects on American eels (Anguilla rostrata)

Curcumin (Cur) exhibits diverse natural pharmacological activities, despite its limited water solubility (hydrophobicity) and low bioavailability. In this investigation, a valine-curcumin conjugate (Val-Cur) was synthesized through amino acid side chain modification, and its solubility increased to 1.78 mg/mL. In vitro experimental findings demonstrated that the antibacterial activity of Val-Cur against Escherichia coli, Staphylococcus aureus, Aeromonas hydrophila, and Vibrio parahaemolyticus was significantly superior to that of Cur. The inhibition rate of Val-Cur against HepG2 (human hepatocellular carcinoma) cells was higher than that of Cur at low concentrations (below 25 μmol/L), although the IC50 value of Val-Cur did not differ significantly from that of Cur. In vivo biological effects of Val-Cur were assessed by adding it into the feed (150 mg/kg) of American eels (Anguilla rostrata). Val-Cur significantly improved the growth performance (↑weight gain rate, ↑specific growth rate, and ↓feed conversion rate) and activities of intestinal digestive enzymes (amylase and lipase) and antioxidant enzymes (superoxide dismutase) in American eels. Additionally, Val-Cur significantly improved serum biochemical indices (↑high-density lipoprotein cholesterol, ↓low-density lipoprotein cholesterol, ↓aspartate and alanine aminotransferases). Furthermore, Val-Cur increased intestinal microbial diversity, reduced the abundance of potentially pathogenic bacteria (Spiroplasma, Clostridium, and Pseudomonas), and elevated the abundance of beneficial digestion-promoting bacteria (Romboutsia, Phyllobacterium, Romboutsia sedimentorum, and Clostridium butyricum) conducive to glucose metabolism (P < 0.05). To the best of our knowledge, this study is the first to explore water-soluble curcumin in aquaculture, and the findings will lay the groundwork for the potential application of water-soluble curcumin in the field of aquaculture.

Configuration of gut bacterial community profile and their potential functionality in the digestive tract of the wild and cultivated Indonesian shortfin elver-phase eels (Anguilla bicolor bicolor McClelland, 1844)

This study aimed to explore the bacteria present in the digestive tracts of wild and cultivated Indonesian shortfin eel during the elver phase. The eel has high export potential due to its vitamin and micronutrient content, but slow growth and vulnerability to collapse in farm conditions hinder its cultivation. The microbiota in the eel's digestive tract is crucial for its health, particularly during the elver phase. This study used Next Generation Sequencing to analyze the community structure and diversity of bacteria in the eels' digestive tracts, focusing on the V3-V4 regions of the 16S rRNA gene. Mothur software was used for data analysis and PAST v.3.26 was used to calculate alpha diversity. The results showed that Proteobacteria (64.18%) and Firmicutes (33.55%) were the predominant phyla in the digestive tract of cultivated eels, while Bacteroidetes (54.16%), Firmicutes (14.71%), and Fusobacteria (10.56%) were predominant in wild eels. The most prevalent genera in cultivated and wild elver were Plesiomonas and Cetobacterium, respectively. The microbiota in the digestive tract of cultivated eels was diverse despite uneven distribution. The KEGG database analysis revealed that the primary function of the microbiome was to facilitate the eel's absorption of nutrients by contributing significantly to the metabolism of carbohydrates and amino acids. This study's findings can aid in assessing eel health and improving eel farming conditions.

Bioactivity of Amaranthus spinosus L. leaf extracts and meals against Aeromonas hydrophila

Plant-based protein is being sought after as a substitute for fish meals (powdered fish) in tilapia feeds. This is to promote sustainable aquaculture, as fish meals contribute to the dwindling marine fish catch. Amaranthus spinosus is an edible weed that shows potential to improve the growth and immunity of Nile tilapia. However, most studies only consider the survivability of fish to evaluate the benefit of using plant-based feeds and do not necessarily elucidate whether a pathogen is affected in vivo. A. spinosus leaf meals (ASLMs) were used to determine effectiveness against Aeromonas hydrophila (BIOTECH 10089) injected intraperitoneally into Nile tilapia. Formulated feeds with fish meals substituted with 50 % (ASLM50) and 75 % (ASLM75) A. spinosus leaves were fed to Nile tilapia challenged with A. hydrophila . Then spleen and kidney tissue were collected and analysed 10 days post-injection for total plate count. The fish fed with ASLM50 appeared healthier than those fed with ASLM75 and those fed with control feeds. Fish fed with ASLMs had lower A. hydrophila counts (P=0.03). Phytochemical screening and antimicrobial activity determination for crude methanolic A. spinosus leaf (ASL) and ASLMs were also conducted to enhance the in vivo results. The metabolites present in the extracts were carbohydrates, amino acids and proteins, cardiac glycosides, saponins and terpenoids. The ASL and ASLM extracts had antimicrobial activity (MIC=115 mg ml−1). Overall, the study showed that ASLMs can make tilapia more resilient against A. hydrophila infections. Fish meal substitution was best at 50 %. Higher substitution had unwanted effects (more bacterial counts), possibly due to antinutritional factors.

Characterization of External Mucosal Microbiomes of Nile Tilapia and Grey Mullet Co-cultured in Semi-Intensive Pond Systems

The external mucosal surfaces of the fish harbor complex microbial communities, which may play pivotal roles in the physiological, metabolic, and immunological status of the host. Currently, little is known about the composition and role of these communities, whether they are species and/or tissue specific and whether they reflect their surrounding environment. Co-culture of fish, a common practice in semi-intensive aquaculture, where different fish species cohabit in the same contained environment, is an easily accessible and informative model toward understanding such interactions. This study provides the first in-depth characterization of gill and skin microbiomes in co-cultured Nile tilapia (Oreochromis niloticus) and grey mullet (Mugil capito) in semi-intensive pond systems in Egypt using 16S rRNA gene-based amplicon sequencing. Results showed that the microbiome composition of the external surfaces of both species and pond water was dominated by the following bacterial phyla: Proteobacteria, Fusobacteriota, Firmicutes, Planctomycetota, Verrucomicrobiota, Bacteroidota, and Actinobacteriota. However, water microbial communities had the highest abundance and richness and significantly diverged from the external microbiome of both species; thus, the external autochthonous communities are not a passive reflection of their allochthonous communities. The autochthonous bacterial communities of the skin were distinct from those of the gill in both species, indicating that the external microbiome is likely organ specific. However, gill autochthonous communities were clearly species specific, whereas skin communities showed higher commonalities between both species. Core microbiome analysis identified the presence of shared core taxa between both species and pond water in addition to organ-specific taxa within and between the core community of each species. These core taxa included possibly beneficial genera such as Uncultured Pirellulaceae, Exiguobacterium, and Cetobacterium and opportunistic potential pathogens such as Aeromonas, Plesiomonas, and Vibrio. This study provides the first in-depth mapping of bacterial communities in this semi-intensive system that in turn provides a foundation for further studies toward enhancing the health and welfare of these cultured fish and ensuring sustainability.

Plesiomonas: A Review on Food Safety, Fish-Borne Diseases, and Tilapia

Fish and fish products are considered a fundamental part of the human diet due to their high nutritional value. Food-borne diseases are considered a major public health challenge worldwide due to their incidence, associated mortality, and negative economic repercussions. Food safety is the guarantee that foods will not cause harm to the health of those who consume them, and it is a fundamental property of food quality. Food safety can be at risk of being lost at any stage of the food chain if the food is contaminated by pathogenic microorganisms. Many diverse bacteria are present in the environment and as part of the microbiota of food that can be transmitted to humans during the handling and consumption of food. Plesiomonas shigelloides has been mainly associated with outbreaks of gastrointestinal diseases due to the consumption of fish. This bacterium inhabits the environment and aquatic animals and is associated with the microbiota of fish such as tilapia, a fish of importance in fishing, aquaculture, commercialization, and consumption worldwide. The purpose of this document is to provide, through a bibliographic review of databases (Scopus, Web of Science, and Google Scholar, among others), a general informative perspective on food-borne diseases and, in particular, the consumption of fish and tilapia. Diseases derived from contamination by Plesiomonas shigelloides are included, and control and prevention actions and sanitary regulations for fishery products established in several countries around the world are discussed to promote the safety of foods of aquatic origin intended for human consumption and to protect public health.

The microbial safety of fish and fish products: Recent advances in understanding its significance, contamination sources, and control strategies

Microorganisms play a crucial and unique role in fish and fish product safety. The presence of human pathogens and the formation of histamine caused by spoilage bacteria make the control of both pathogenic and spoilage microorganisms critical for fish product safety. To provide a comprehensive and updated overview of the involvement of microorganisms in fish and fish product safety, this paper reviewed outbreak and recall surveillance data obtained from government agencies from 1998 to 2018 and identified major safety concerns associated with both domestic and imported fish products. The review also summarized all available literature about the prevalence of major and emerging microbial safety concerns, including Salmonella spp., Listeria monocytogenes, and Aeromonas hydrophila, in different fish and fish products and the survival of these pathogens under different storage conditions. The prevalence of antibiotic-resistant bacteria (ARB) and antibiotic-resistant genes (ARGs), two emerging food safety concerns, is also reviewed. Pathogenic and spoilage microorganisms as well as ARB and ARGs can be introduced into fish and fish products in both preharvest and postharvest stages. Many novel intervention strategies have been proposed and tested for the control of different microorganisms on fish and fish products. One key question that needs to be considered when developing and implementing novel control measures is how to ensure that the measures are cost and environment friendly as well as sustainable. Over the years, regulations have been established to provide guidance documents for good farming and processing practices. To be more prepared for the globalization of the food chain, harmonization of regulations is still needed.

Combined Effect of Modified Atmosphere Packaging and UV-C Radiation on Pathogens Reduction, Biogenic Amines, and Shelf Life of Refrigerated Tilapia (Oreochromis niloticus) Fillets

This study investigated the isolated effect of modified atmosphere packaging (MAP; 50% CO₂ and 50% N₂) and ultraviolet radiation (UV; 0.30 J/cm²) as well as their combined (MAP/UV) effect on reduction of Salmonella typhimurium and Escherichia coli O157:H7, biogenic amines (BA), and on shelf life of tilapia fillets stored at 4 ± 1 °C for 10 days. UV samples had the highest reduction of S. typhimurium (1.13 log colony forming units/g; CFU/g) and E. coli O157:H7 (0.70 log CFU/g). MAP and MAP/UV reduced the growth of S. typhimurium in 0.50 log CFU/g and did not affect the growth of E. coli O157:H7. UV, MAP, and MAP/UV increased lag phase and/or generation time of all evaluated bacterial groups, decreased pH values, ammonia formation, texture changes, and, in general, the BA formation throughout storage period, and, therefore, UV, MAP, and MAP/UV extended the shelf life for two, three, and at least five days, respectively. MAP/UV, MAP, and UV decreased redness, MAP/UV and MAP increased yellowness and lipid oxidation, while UV did not affect it. MAP/UV demonstrated promising results for shelf life extension; however, different gas ratios in combination with other ultraviolet radiation type C (UV-C) doses should be investigated to reach the highest microbiological safety and maintenance of the overall quality of tilapia fillets.

Effects of woody forages on biodiversity and bioactivity of aerobic culturable gut bacteria of tilapia (Oreochromis niloticus)

The present study investigated the effects of four woody forages (Moringa oleifera Lam (MOL), fermented MOL, Folium mori (FM) and fermented FM) on biodiversity and bioactivity of aerobic culturable gut bacteria of tilapia (Oreochromis niloticus) by a traditional culture-dependent method. A total of 133 aerobic culturable isolates were recovered and identified from the gut of tilapia, belonging to 35 species of 12 genera in three bacterial phyla (Firmicutes, Actinobacteria and Proteobacteria). Among them, 6 bacterial isolates of Bacillus baekryungensis, Bacillus marisflavi, Bacillus pumilus, Bacillus methylotrophicus, Proteus mirabilis and Pseudomonas taiwanensis were isolated from all the five experimental groups. The Bray-Curtis analysis showed that the bacterial communities among the five groups displayed obvious differences. In addition, this result of bioactivity showed that approximate 43% of the aerobic culturable gut bacteria of tilapia displayed a distinct anti-bacterial activity against at least one of four fish pathogens Streptococcus agalactiae, Streptococcus iniae, Micrococcus luteus and Vibrio parahemolyticus. Furthermore, Bacillus amyloliquefaciens and Streptomyces rutgersensis displayed strong activity against all four indicator bacteria. These results contribute to our understanding of the intestinal bacterial diversity of tilapia when fed with woody forages and how certain antimicrobial bacteria flourished under such diets. This can aid in the further exploitation of new diets and probiotic sources in aquaculture.

Molecular Typing, Antibiogram and PCR-RFLP Based Detection of Aeromonas hydrophila Complex Isolated from Oreochromis niloticus

Motile Aeromonas septicemia is a common bacterial disease that affects Oreochromis niloticus and causes tremendous economic losses globally. In order to investigate the prevalence, molecular typing, antibiogram and the biodiversity of Aeromonas hydrophila complex, a total of 250 tilapia (Oreochromis niloticus) were collected randomly from 10 private tilapia farms (25 fish/farm) at El-Sharkia Governorate, Egypt. The collected fish were subjected to clinical and bacteriological examinations. The majority of infected fish displayed ulcerative necrosis, exophthalmia, and internal signs of hemorrhagic septicemia. The prevalence of A. hydrophia complex was 13.2%, where the liver was the most predominant affected organ (54.1%). Polymerase chain reaction (PCR) was used to verify the identification of A. hydrophila complex using one set of primers targeting gyrB as well as the detection of virulent genes (aerA, alt, and ahp). All isolates were positive for the gyrB-conserved gene and harbored aerA and alt virulence genes. However, none of those isolates were positive for the ahp gene. The antimicrobial sensitivity was carried out, where the recovered strains were completely sensitive to ciprofloxacin and highly resistant to amoxicillin. All retrieved strains showed the same phenotypic characteristics and were identical based on the restriction fragment length polymorphism (RFLP). Experimentally challenged fish presented a high mortality rate (76.67%) and showed typical signs as in naturally infected ones. In conclusion, the synergism of phenotypic and genotypic characterization is a valuable epidemiological tool for the diagnosis of A. hydrophila complex. RFLP is a fundamental tool for monitoring the biodiversity among all retrieved strains of A. hydrophia.

Combined effect of oxygen-scavenger packaging and UV-C radiation on shelf life of refrigerated tilapia (Oreochromis niloticus) fillets

This study investigated the physicochemical, instrumental and bacterial parameters of tilapia fillets subjected to oxygen-scavenger packaging, alone or in combination with UV-C radiation at two doses (0.102 and 0.301 J/cm²), stored at 4 ± 1 °C for 23 days. The oxygen scavenger, both UV-C doses, and the oxygen scavenger combined with UV-C, independently of the dose, extended the shelf life in 5, 6 and 7 days, respectively, by decreasing the bacterial growth rate and the formation of degradation compounds (e.g., TVB-N and ammonia). Oxygen-scavenger packaging, alone or in combination with UV-C at 0.102 J/cm² and 0.301 J/cm² showed lower amounts of free amino acids (FAA; 34.39, 34.49 and 34.50 mg L-lysine/kg fish tissue, 3.63, 3.57 and 3.61 mg L- ornithine/kg fish tissue, 27.52, 27.63 and 27.67 mg L-arginine/kg fish tissue), biogenic amines (BA; 3.81, 3.87 and 3.89 mg cadaverine/kg fish tissue, 12.88, 12.91 and 12.86 mg putrescine/kg fish tissue, 2.41, 2.44 and 2.47 mg spermidine/kg fish tissue), redness (2.53, 2.55 and 2.59), yellowness (6.65, 6.69 and 6.72), lipid oxidation (1.52, 1.53 and 1.58 mg malondialdehyde/kg fish tissue) and protein oxidation (5.06, 5.11 and 5.18 nmol carbonyls/mg protein), with higher hardness (3273.41, 2652.98 and 2687.57 g) than control (air packaging; 41.97 mg L-lysine/kg fish tissue, 4.83 mg L- ornithine/kg fish tissue, 37.33 mg L-arginine/kg fish tissue, 4.82 mg cadaverine/kg fish tissue, 16.56 mg putrescine/kg fish tissue, 3.21 mg spermidine/kg fish tissue, 4.26 of redness, 8.17 of yellowness, 2.88 mg malondialdehyde/kg fish tissue, 9.44 nmol carbonyls/mg protein and 2092.58 g of hardness), respectively, on day 13 of storage when the control fillets were unfit for consumption (7 log CFU/g) (p < 0.05). However, in the same day of storage, both UV-C doses had similar values for BA (p > 0.05), higher amounts of FAA (44.28 and 44.13 mg L-lysine/kg fish tissue, 5.16 and 5.12 mg L- ornithine/kg fish tissue, 40.20 and 40.28 mg L-arginine/kg fish tissue), redness (4.86 and 5.33), yellowness (9.32 and 10.01), lipid oxidation (3.09 and 3.52 mg malondialdehyde/kg fish tissue) and protein oxidation (10.27 and 11.93 nmol carbonyls/mg protein), as well as lower hardness (1877.54 and 1767.39 g), respectively, than control fillets (p < 0.05). The combined preservation methods were the most effective in extending the shelf life and prolonging the physicochemical quality of the refrigerated tilapia fillets and the O₂ scavenger proved to be a potential alternative to prevent the negative changes induced by both UV-C doses.

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.

High fat diet worsens the adverse effects of antibiotic on intestinal health in juvenile Nile tilapia (Oreochromis niloticus)

Antibiotics and high fat diets are commonly used independently in global aquaculture production for fish health management and to spare the use of costly protein as energy sources, respectively, causing relatively similar metabolic effects and stresses. However, it is unknown whether dietary high fat worsens or attenuates the adverse effects caused by antibiotics in fish. We determined the ability of high fat diet to influence the adverse effects of oxytetracycline on Nile tilapia, Oreochromis niloticus. Thirty Nile tilapia weighing 8.45 ± 0.15 g were fed on medium fat (MF; 70 g/kg) and high fat (HF; 120 g/kg) diets and the same fat levels supplemented with 2.00 g/kg diet of OTC (80 mg/kg body weight/day) hereafter, MFO and HFO for 65 days. The general growth performance, feed efficiency and intestinal health of fish were evaluated. The Nile tilapia fed on HFO diet had significantly lower growth rate, body protein content and feed efficiency compared to those fed on MFO diet. Dietary HFO affected the intestine histomorphology, which decreased dramatically the tight junction proteins of Nile tilapia and induced microbiota dysbiosis compared to MFO diet. The Nile tilapia fed on HFO diet had increased oxidative stress, which stimulated drug detoxification response, caused endoplasmic reticulum stress and apoptosis compared to those fed on MFO diet. The new findings from our study demonstrate that, the adverse effects of antibiotics in fish are different at medium and high fat contents. Feeding fish with high fat diets with antibiotics worsen the adverse effects. This enlightens our understanding on the risks of antibiotics misuse and also suggests that antibiotics should be more strictly limited in aquaculture, in which high fat diets are currently widely used in fish production worldwide.

Effects of dietary probiotic supplementation on the growth, gut health and disease resistance of juvenile Nile tilapia (Oreochromis niloticus)

This study investigated the effects of the Streptococcus agalactiae antagonizing probiotics Bacillus cereus NY5 and Bacillus subtilis as feed additives for Nile tilapia in terms of growth performance, intestinal health and resistance to S. agalactiae. A total of 720 apparently healthy juvenile Nile tilapia (0.20 ± 0.05 g) were randomly divided into 4 equal groups with 3 replicates for each group. Fish were fed a basal diet (control check group, CK group) supplemented with B. subtilis (1 × 10⁸ CFU/g feed, BS group), B. cereus NY5 (1 × 10⁸ CFU/g feed, BC group), and B. subtilis + B. cereus NY5 (0.5 × 10⁸ CFU/g feed of each probiotic, BS + BC group) for 6 wk, and the probiotic supplementation groups were then fed the basal diet for 1 wk to investigate the gut microbial community. The results of this study showed that BS + BC and BC treatments significantly increased weight gain (WG), feed conversion ratio (FCR) and S. agalactiae resistance in Nile tilapia (P < 0.05). Gut microvilli length and density and c-type lysozyme (lyzc) gene expression were significantly increased by probiotic supplementation (P < 0.05). The results of high-throughput sequencing showed that the B. cereus NY5 and B. subtilis + B. cereus NY5-supplemented feed resulted in a significant improvement in tilapia autochthonous gut bacterial communities and had a stimulation effect on a variety of potential probiotics after 6 wk of feeding. After cessation of probiotic administration for 1 wk, the gut bacteria of the fish in the BS + BC and BC groups had minor changes and maintained a stable state. Consequently, it was inferred that, as a feed supplement, B. cereus NY5 and the mixture of B. subtilis and B. cereus NY5 at 1 × 10⁸ CFU/g feed were able to promote growth and disease resistance, which may be associated with the supplement's effects on gut immune status, intestinal morphology, and intestinal microbial community composition.

Genotypic diversity among Shewanella spp. collected from freshwater fish

Different Shewanella species are isolated both from healthy and from diseased fish. To date, contemporary methods do not provide sufficient insight to determine species and detail differentiation between tested strains. Bacteria isolated from cultured (n = 33), wild (n = 12) and ornamental (n = 6) fish, as well as several reference strains, were tested by 16S rRNA gene sequencing, ERIC-PCR and pulsed-field gel electrophoresis (PFGE) assays. Our study indicates that isolates collected from freshwater fish were genetically diverse. Based on 16S rRNA gene sequences, bacteria were clustered into groups S. putrefaciens, S. xiamenensis and S. oneidensis. Some isolates were classified only to genus Shewanella; thus, 16S rRNA gene analyses were not enough to determine the species. ERIC-PCR revealed 49 different genotype profiles indicating that the method might be useful for differentiation of Shewanella isolates irrespectively to species identification, contrary to PFGE which is not suitable for Shewanella typing.

Effects of Lactococcus lactis subsp. lactis JCM5805 on colonization dynamics of gut microbiota and regulation of immunity in early ontogenetic stages of tilapia

The administration of probiotics during early ontogenetic stages can be an effective way to manipulate the gut microbiota of animals. Specifically, the administration of probiotics can enhance gut-colonization success and regulate the immune response. In this study, the effects of early contact with probiotic Lactococcus lactis subsp. lactis JCM5805 on the gut microbial assembly of larvae Nile tilapia were examined. The effects of JCM5805 on IFNα expression through the TLR7 and TLR9-dependent signal transduction pathway as well as larval disease resistance were studied. Three days postfertilization, embryos were randomly allocated into nine 30 L tanks with a concentration of 20 eggs L^-1. Triplicate tanks were performed for each treatment. Treatments included a control group (C), a low probiotic concentration group (T1), where JCM5805 was added to the water at 1 × 10⁴ cfu ml^-1, and a high probiotic concentration group (T2), where JCM5805 was added to the water at 1 × 10⁸ cfu ml^-1. Probiotics were administered continuously for 15 days. qPCR was used to analyze transcript levels of the TLR7, TLR9, MyD88, IRF7 and IFNα genes using RNA extracted from whole embryos on day 5 and 10, and from the intestine of larvae on day 15. Transcription of these genes was also measured in the intestine, liver and spleen of larvae one month after the cessation of probiotic administration. The results showed that MyD88 and IRF7 were significantly elevated on days 5 and 10 in the T2 group. TLR9 and IFNα were also significantly elevated on days 5, 10 and 15 during probiotic application of T2 (P < 0.05). One month after the cessation of probiotics administration, no significant difference was observed in the expression of these genes (P > 0.05). The larvae were fed probiotics for 15 days and were infused with Streptococcus agalactiae strain WC1535 at a final concentration of 1 × 10⁶ cfu ml^-1. The survival rate of T2 was significantly higher than that of the C group (P < 0.05). Microbial characterization by Illumina HiSeq sequencing of 16S rRNA gene amplicons showed the significantly higher presence of JCM5805 in the guts of T2 after 15 days of probiotic continuous application. Although JCM5805 was below the detection level after the cessation of probiotic for 5 days, the gut microbiota of the exposed tilapia larvae in T2 remained clearly different from that of the control treatment after the cessation of probiotic administration. These data indicated that a high concentration of the probiotic strain JCM5805 upregulated the expression of IFNα via the TLR7/TLR9-Myd88 pathway and enhanced disease resistance of larvae. JCM5805 was only transiently detected and thus was not included in the stable larval microbiota. The early microbial exposure of tilapia larvae affects the gut microbiota at later life stages. However, whether the upregulation of related genes is related to the presence of JCM5805 strain in the intestine requires further verification.

Microbial mediated sedimentary phosphorus mobilization in emerging and eroding wetlands of coastal Louisiana

The interactions between the microbial reduction of Fe (III) oxides and sediment geochemistry are poorly understood and mostly unknown for the Louisiana deltaic plain. This study evaluates the potential of P mobilization for this region during bacterially mediated redox reactions. Samples were collected from two wetland habitats (forested wetland ridge, and marsh) characterized by variations in vegetation structure and elevation in the currently prograding Wax Lake Delta (WLD) and two habitats (wetland marsh, and benthic channel) in degrading Barataria Bay in Lake Cataouatche (BLC). Our results show that PO₄^3- mobilization from WLD and BLC habitats were negligible under aerobic condition. Under anaerobic condition, there is a potential for significant release of PO₄^3- from sediment and wetland soils. PO₄^3- release in sediments spiked with Fe reducing bacteria Shewanella putrefaciens (Sp-CN32) were significantly higher in all cases with respect to a control treatment. In Wax Lake delta, PO₄^3- release from sediment spiked with Sp-CN32 increased significantly from 0.064±0.001 to 1.460±0.005μmolg^-1 in the ridge and from 0.079±0.007 to 2.407±0.001μmolg^-1 in the marsh substrates. In Barataria bay, PO₄^3- release increased from 0.103±0.006μmolg^-1 to 0.601±0.008μmolg^-1 in the channel and 0.050±0.000 to 0.618±0.026μmolg^-1 in marsh substrates. The PO₄^3- release from sediment slurries spiked with Sp-CN32 was higher in the WLD habitats (marsh 30-fold, ridge 22-fold) compared to the BLC habitats (marsh 12-fold, channel 6-fold). The increase in PO₄^3- release was significantly correlated with the Fe bound PO₄^3- in sediments from different habitats but not with their organic matter content. This study contributes to our understanding of the release mechanism of PO₄^3- during bacterial mediated redox reaction in wetland soils undergoing pulsing sediment deposition and loss.

Effects of dietary blackberry syrup supplement on growth performance, antioxidant, and immunological responses, and resistance of Nile tilapia, Oreochromis niloticus to Plesiomonas shigelloides

The present study investigated the effects of dietary blackberry syrup on growth performance, haematological, non-specific immune and spleen gene expression responses of Nile tilapia, Oreochromis niloticus. Five experimental groups of fish with mean weights of 26.75 ± 2.67 g were used in the study; three of them were fed with blackberry syrup incorporated diets (7.5 g kg^-1- BBRY7.5, 15 g kg^-1- BBRY15, 30 g kg^-1- BBRY30), whereas an additive free basal diet served as the control. Additionally, the fifth group was an antibiotic medicated diet (0.02 g kg^-1- ABTC), prepared with the florfenicol. Dietary blackberry syrup especially at 15 g kg^-1 significantly increased growth performance, respiratory burst activity, potential killing activity, phagocytic activity, phagocytic index, lysozyme activity, myeloperoxidase activity, total immunoglobulin levels, serum SOD activity and serum CAT activity (p < 0.05). Furthermore, dietary blackberry syrup increased the expression levels of immune [heat shock protein 70 (HSP70), interleukin 1, beta (IL-1β), tumor necrosis factor (TNF-α), interferon gamma (IFN-γ), immunoglobulin M (IgM)] and antioxidant [glutathione peroxidase (GPx)] related genes in the spleen of fish fed with especially 15 g kg^-1 blackberry syrup (p < 0.05). At the end of the 20-day challenge period the survival rates were significantly higher in the BBRY15 and ABTC groups compared to all other treatment groups (p < 0.05). As a result, feeding Nile tilapia with a diet containing 15 g kg^-1 blackberry syrup over a period of 90 days might be adequate to improve growth performance, fish immune parameters, antioxidant status, as well as survival rate against P. shigelloides, similar to antibiotic treatment. Hence, blackberry syrup can be used as an antibiotics replacer for controlling P. shigelloides in tilapia feed.

Effects of dietary Lactobacillus rhamnosus JCM1136 and Lactococcus lactis subsp. lactis JCM5805 on the growth, intestinal microbiota, morphology, immune response and disease resistance of juvenile Nile tilapia, Oreochromis niloticus

The present study aimed to evaluate the individual and combined effects of Lactobacillus rhamnosus (LR) JCM1136 and Lactococcus lactis subsp. lactis (LL) JCM5805 on the growth, intestinal microbiota, intestinal morphology, immune response and disease resistance of juvenile Nile tilapia (Oreochromis niloticus). A total of 720 apparently healthy juvenile Nile tilapia (0.20 ± 0.05 g) were randomly divided into four equal groups. Fish were fed with a basal diet (CK) supplemented with JCM1136 (LR), JCM5805 (LL), and JCM1136 + JCM5805 (LR+LL) at 1 × 10⁸ CFU/g basal diet for 6 weeks, followed by a basal diet for 1 week. After 6 weeks of feeding, the LL treatment significantly increased the growth and feed utilization of Nile tilapia when compared with the CK. Light microscopy and transmission electron microscopy images of the midgut revealed that probiotic supplementation significantly increased gut microvilli length and microvilli density compared to CK. The transcript levels of several key immune-related genes in the mid-intestine and liver of fish were analyzed by means of quantitative polymerase chain reaction (qPCR) at the end of the sixth week. The results showed the following: when compared to CK group, fish in LR had significantly increased transcript levels of IFN-γ, lyzc, hsp70 and IL-1β in the intestine; LL fish showed significantly increased expressions of TNF-α, IFN-γ, lyzc, hsp70 and IL-1β in the intestine and liver; and intestine lyzc, hsp70 and IL-1β and liver TNF-α, IFN-γ, hsp70 and IL-1β were significantly increased in LR+LL fish. Following a 6-week period of being fed probiotics or a control diet, the tilapia were challenged with an intraperitoneal injection of 20 μl of the pathogenic Streptococcus agalactiae (WC1535) (1 × 10⁵ CFU/ml). The survival rates of the probiotic-fed groups were significantly higher than that of the CK group, and the LL group had the highest survival rate. High-throughput sequencing revealed a significantly higher presence of JCM5805 in the guts of LL fish during the period of probiotic application, but this was no longer detected in all LL samples 1 week post cessation of probiotic administration. Cessation of probiotic administration led to disorders of individual gut microbes within the LR and LL groups. Statistical analysis (LEfSe) demonstrated that three phyla, namely, Bacteroidetes, Fusobacteria and Actinobacteria were enriched in the CK group, while the abundance of Proteobacteria was greater in the probiotic-fed fish. At the genus level, Plesiomonas, which includes potential pathogens of fish, were significantly decreased in the probiotic-fed groups. In contrast, a significant increase of Rhizobium and Achromobacter, which can produce a variety of enzymes with cellulolytic and pectolytic activity, were observed in fish fed with probiotics, indicating that dietary probiotics were helpful in the propagation of some probiotic bacteria. Our data revealed that JCM1136 and JCM5805, as a feed additive at 10⁸ CFU/g feed, could improve intestinal morphology, enhance immune status and disease resistance, and affect the gut microbiota of tilapia; thus, these additives could be used as probiotics for juvenile Nile tilapia. JCM5805 was more effective than JCM1136 or the mixture of the two for promoting the growth, enhancing the immune status and disease resistance of tilapia.

Analysis of potential risks from the bacterial communities associated with air-contact surfaces from tilapia (Oreochromis niloticus) fish farming

Tilapia farming is a promising growing sector in aquaculture. Yet, there are limited studies on microbiological risks associated to tilapia farms. The aim of the present study was to analyse the bacterial communities from solid surfaces in contact with air in a tilapia farm in order to evaluate the presence of bacteria potentially toxinogenic or pathogenic to humans or animals. Samples from a local tilapia farm (tank wall, aerator, water outlets, sink and floor) were analyzed by high throughput sequencing technology. Sequences were assigned to operational taxonomic units (OTUs). Proteobacteria was the main phylum represented in most samples (except for one). Cyanobacteria were a relevant phylum in the inner wall from the fattening tank and the wet floor by the pre-fattening tank. Bacteroidetes were the second phylum in relative abundance for samples from the larval rearing tank and the pre-fattening tank and one sample from the fattening tank. Fusobacteria showed highest relative abundances in samples from the larval rearing tank and pre-fattening tank. Other phyla (Verrucomicrobia, Actinobacteria, Firmicutes, Planktomycetes, Acidobacteria, Chloroflexi, Chlorobi, Gemmatiomonadetes or Fibrobacters) had lower relative abundances. A large fraction of the reads (ranging from 43.67% to 72.25%) were assigned to uncultured bacteria. Genus Acinetobacter (mainly A. calcoaceticus/baumanni) was the predominant OTU in the aerator of the fattening tank and also in the nearby sink on the floor. The genera Cetobacterium and Bacteroides showed highest relative abundances in the samples from the larval rearing tank and the pre-fattening tank. Genera including fish pathogens (Fusobacterium, Aeromonas) were only detected at low relative abundances. Potential human pathogens other than Acinetobacter were either not detected or had very low relative abundances (< 0.01%). The results of the study suggest that the main risk factors to be monitored in tilapia farm are putative human pathogenic Acinetobacter and potential cyanotoxin-producing cyanobacteria.

Quantitative analyses of the bacterial microbiota of rearing environment, tilapia and common carp cultured in earthen ponds and inhibitory activity of its lactic acid bacteria on fish spoilage and pathogenic bacteria

The present study aimed to evaluate the bacterial load of water, Nile Tilapia and common Carp intestines from earthen ponds, isolate lactic acid bacteria (LAB) and assess their antimicrobial activity against fish spoilage and pathogenic bacteria. Following enumeration and isolation of microorganisms the antimicrobial activity of the LAB isolates was evaluated. Taxonomic identification of selected antagonistic LAB strains was assessed, followed by partial characterisation of their antimicrobial metabolites. Results showed that high counts (>4 log c.f.u ml^-1 or 8 log c.f.u g^-1) of total aerobic bacteria were recorded in pond waters and fish intestines. The microbiota were also found to be dominated by Salmonella spp., Vibrio spp., Staphylococcus spp. and Escherichia coli. LAB isolates (5.60%) exhibited potent direct and extracellular antimicrobial activity against the host-derived and non host-derived spoilage and pathogenic bacteria. These antagonistic isolates were identified and Lactococcus lactis subsp. lactis was found as the predominant (42.85%) specie. The strains displayed the ability to produce lactic, acetic, butyric, propionic and valeric acids. Bacteriocin-like inhibitory substances with activity against Gram-positive and Gram-negative (Vibrio spp. and Pseudomonas aeruginosa) bacteria were produced by three L. lactis subsp. lactis strains. In this study, the LAB from the microbiota of fish and pond water showed potent antimicrobial activity against fish spoilage or pathogenic bacteria from the same host or ecological niche. The studied Cameroonian aquatic niche is an ideal source of antagonistic LAB that could be appropriate as new fish biopreservatives or disease control agents in aquaculture under tropical conditions in particular or worldwide in general.

Shewanella putrefaciens – a new opportunistic pathogen of freshwater fish

In recent years, Shewanella putrefaciens, commonly known as a halophilic bacteria, has been associated with serious health disorders in freshwater fish. Therefore, it has been described as a new aetiological agent of the disease, named shewanellosis. S. putrefaciens is a heterogeneous group of microorganisms, belonging to the Alteromonadaceae family. Based on different criteria, three biovars and biogroups as well as four genomic groups have been distinguished. The first infections of S. putrefaciens in fish were reported in rabbitfish (Siganus rivulatus) and European sea bass (Dicentrarchus labrax L.). Outbreaks in farmed fish were reported in Poland for the first time in 2004. The disease causes skin disorders and haemorrhages in internal organs. It should be noted that S. putrefaciens could also be associated with different infections in humans, such as skin and tissue infections, bacteraemia, otitis. Investigations on pathogenic mechanisms of S. putrefaciens infections are very limited. Enzymatic activity, cytotoxin secretion, adhesion ability, lipopolysaccharide (LPS), and the presence of siderophores are potential virulence factors of S. putrefaciens. Antimicrobial resistance of S. putrefaciens is different and depends on the isolates. In general, these bacteria are sensitive to antimicrobial drugs commonly used in aquaculture.

Standardizing the microbiota of fish used in research

Little attention has been paid to the effects of fish microbiotas on the reproducibility and comparability of fish studies so far. Extrinsic and intrinsic factors, such as water quality, environmental microbial populations, diet, host genetic profile, gender, age and stress status, affect fish microbiotas and create significant inter- and intra-species variations. Fish microbiotas play critical roles in many key aspects of host physiology, such as protection against pathogens, digestion and development of the digestive tract and the local immune system. Thus, greater effort should be invested in standardizing the microbiological profiles of research fish. In this context, issues requiring consideration include the establishment of isogenic and isobiotic fish lines, the standardization of rearing conditions and the development of appropriate tests to adequately describe microbial populations. There are many challenges involved in each of these issues, and the research community must decide which aspects should be standardized for each species and each type of research. For all studies in which microbiota is expected to exert an influence, thorough reporting is of paramount importance. Every step towards standardization increases study quality and simultaneously contributes to reducing the number of fish used in research, which is a legal and ethical obligation.

Plesiomonas shigelloides Revisited

After many years in the family Vibrionaceae, the genus Plesiomonas, represented by a single species, P. shigelloides, currently resides in the family Enterobacteriaceae, although its most appropriate phylogenetic position may yet to be determined. Common environmental reservoirs for plesiomonads include freshwater ecosystems and estuaries and inhabitants of these aquatic environs. Long suspected as being an etiologic agent of bacterial gastroenteritis, convincing evidence supporting this conclusion has accumulated over the past 2 decades in the form of a series of foodborne outbreaks solely or partially attributable to P. shigelloides. The prevalence of P. shigelloides enteritis varies considerably, with higher rates reported from Southeast Asia and Africa and lower numbers from North America and Europe. Reasons for these differences may include hygiene conditions, dietary habits, regional occupations, or other unknown factors. Other human illnesses caused by P. shigelloides include septicemia and central nervous system disease, eye infections, and a variety of miscellaneous ailments. For years, recognizable virulence factors potentially associated with P. shigelloides pathogenicity were lacking; however, several good candidates now have been reported, including a cytotoxic hemolysin, iron acquisition systems, and lipopolysaccharide. While P. shigelloides is easy to identify biochemically, it is often overlooked in stool samples due to its smaller colony size or relatively low prevalence in gastrointestinal samples. However, one FDA-approved PCR-based culture-independent diagnostic test system to detect multiple enteropathogens (FilmArray) includes P. shigelloides on its panel. Plesiomonads produce β-lactamases but are typically susceptible to many first-line antimicrobial agents, including quinolones and carbapenems.