Bacterial Challenge Test Research Articles

Evaluation of inhibitory, immunomodulatory, survival, and growth effects of host-derived Weissella confusa on Macrobrachium rosenbergii challenged with Vibrio parahaemolyticus

Macrobrachium rosenbergii is a highly valuable prawn species in aquaculture due to its current growing demand in the market. However, various bacterial diseases caused by Vibrio parahaemolyticus have been observed to induce mortality in larval, juvenile, and adult stages of M. rosenbergii. While antibiotics are commonly used to manage these diseases, they contribute to antimicrobial resistance, a global concern with serious environmental and health implications. Consequently, the scientific community is exploring host-derived beneficial microorganisms as functional feed additives, offering eco-friendly alternatives that boost shrimp and prawn immunity. The purpose of this study was to examine the effects of host-derived beneficial microorganisms from the gut of M. rosenbergii, on the inhibition, immunomodulation, survival, and growth of M. rosenbergii when exposed to V. parahaemolyticus. The result of this study showed that Weissella confusa C6, a lactic acid bacterium isolated from the gut of M. rosenbergii, significantly inhibits the growth of V. parahaemolyticus R1 as demonstrated in agar well diffusion assay and co-culture assay. Additionally, it showed immunomodulatory effects, indicated by elevated total hemocyte count (THC) and phenoloxidase (PO) activity during the bacterial challenge test. Furthermore, supplementing the diet with W. confusa led to significant improvements in M. rosenbergii, including increased survival rates, weight gain, specific growth rate, better feed conversion ratio, and reduced density of V. parahaemolyticus in the prawn's gut. Therefore, it can be considered a viable option for use as a feed supplement in prawn farming, enhancing M. rosenbergii's immune system, disease resistance, and overall health.

In vitro evaluation of two novel Escherichia bacteriophages against multiple drug resistant avian pathogenic Escherichia coli.

In recent years, there has been a growing interest in phage therapy as an effective therapeutic tool against colibacillosis caused by avian pathogenic Escherichia coli (APEC) which resulted from the increasing number of multidrug resistant (MDR) APEC strains. In the present study, we reported the characterization of a new lytic bacteriophage (Escherichia phage AG- MK-2022. Basu) isolated from poultry slaughterhouse wastewater. In addition, the in vitro bacteriolytic activity of the newly isolated phage (Escherichia phage AG- MK-2022. Basu) and the Escherichia phage VaT-2019a isolate PE17 (GenBank: MK353636.1) were assessed against MDR- APEC strains (n = 100) isolated from broiler chickens with clinical signs of colibacillosis. Escherichiaphage AG- MK-2022. Basu belongs to the Myoviridae family and exhibits a broad host range. Furthermore, the phage showed stability under a wide range of temperatures, pH values and different concentrations of NaCl. Genome analysis of the Escherichia phage AG- MK-2022. Basu revealed that the phage possesses no antibiotic resistance genes (ARGs), mobile genetic elements (MGEs), and any E. coli virulence associated genes. In vitro bacterial challenge tests demonstrated that two phages, the Escherichia phage VaT-2019a isolate PE17 and the Escherichia phage AG- MK-2022. Basu exhibited high bactericidal activity against APEC strains and lysed 95% of the tested APEC strains. The current study findings indicate that both phages could be suggested as safe biocontrol agents and alternatives to antibiotics for controlling MDR-APEC strains isolated from broilers.

Synbiotic encapsulation against Vibrio parahaemolyticus infection in whiteleg shrimps

Vibrio parahaemolyticus is a severe pathogenic bacterium which causes significant mortality and economical loss in shrimp farming. To control vibriosis in whiteleg shrimps (Litopenaeus vannamei), we developed synbiotic beads by microencapsulating probiotic of Lactobacillus plantarum and prebiotic of xanthan gum in agarose matrix through emulsion technique. Coculture method indicated that synbiotic beads reduce viability of Vibrio parahaemolyticus by 3 orders of magnitude. The high inhibitory activity of synbiotic beads against pathogen could result from the antibacterial substances secreted from encapsulated probiotics, and access blocking of pathogens to prebiotics as food source so that the encapsulated prebiotics solely stimulate nearby probiotic growth without boosting pathogen growth. Bacterial challenge test indicated that exposure to synbiotic beads in advance can delay mortality and increase shrimp survival from 10% to 57%. As a smart encapsulation platform, our design can be extended to various probiotics, prebiotics, and pathogens, thus providing an alternative strategy to the use of antibiotics for disease prevention and sustainable aquaculture.

Biological control of Pseudomonas aeruginosa (ATCC-27853) by isolated lytic bacteriophage

Background Pseudomonas aeruginosa is a common bacterial species; it can grow in all fields, even in distilled water. One of the obvious characteristics of P. aeruginosa species is its low antibiotic susceptibility (antibiotic-multi-resistant species); this reflects the urgent need for alternative strategies. Unconventionally, we try to use an alternative destructive antibacterial agent, phage. phage application in our environmental fields (engineering relevance) is a promising safe avenue for replacing chemical biocides. Objective To isolate a lytic phage as a bio-control agent for Pseudomonas aeruginosa (ATCC-27853), evaluate the ability of the isolated phage to inhibit or suppress the growth of the target bacteria. We study phage stability while performing biological and physical characterization, optimizing phage action against bacteria. Materials and methods We use an activated, purified young culture of Pseudomonas aeruginosa (ATCC-27853) as the target bacteria to isolate a specific lytic bacteriophage from a mixture of Enriched sewage and marine water through a sequence of experiments: a Broth clearing assay using nutrient broth and a spot assay test by using nutrient agar medium, both for the detection of phage presence and its lytic action. For the purification of phage, the plaque assay test was performed in many successive subcultures by using the serial dilution method on a semisolid medium. The high-titer lysate obtained from the confluent plates was investigated by TEM to determine its morphology and taxonomy. We performed biological characterization of the isolated phage: one-step growth curve, Phage adsorption rate, host range (using nutrient double layer agar), as well as a bacterial challenge test (using nutrient broth, based on the optical densities). Also, we performed physical characterization of the phage to determine phage Stability, pH, thermal stability, and the influence of UV and organic solvents on the lytic action of the phage. Results and conclusion Pyocyanin and pyoverdin pigments (both fluorescent under UV illumination) are secreted by P. aeruginosa (ATCC-27853), also their ability to thrive at 42°C. After spotting P. aeruginosa plates with enriched sewage filtrate, the results indicated lytic area (+ve). Plaques have a pin tip and are translucent. The lytic profile of bacteria after phage infection revealed that the bacteria was reduced to a MOI of 10 in 4 h. However, the multiplicity of infection(MOI) of 1 and 0.01, respectively, was longer (10, 22/h). The electron microscopy revealed that the phage is a member of the podoviridae family, with a noncontractile short tail (18 nm) and a polyhedral (heptagonal) head (45 nm) in diameter and a phage length of 63 nm. The adsorption rate of the phage was greatest at 20 min. Our goal with the phage application is to replace harmful chemical biocides with lytic bacteriophages in various environmental systems (Phage for Biological Control). Phage bio-control treatment thus holds promise for eliminating the requirement for hazardous chemical biocides.

The Potential of Fish Protein Hydrolysate Supplementation in Nile Tilapia Diets: Effects on Growth and Health Performance, Disease Resistance, and Farm Economic Analysis.

Fish protein hydrolysate (FPH) has shown immense potential as a dietary protein supplement and immunostimulant in aquaculture, especially in Nile tilapia production. Four isoproteic diets (30% crude protein) were prepared by including FPH at varying percentages (0%, 0.5%, 1%, and 2%). Nile tilapia fed with FPH diets for 90 days, and their growth performance, feed utilization, blood biochemistry, liver and gut morphology, and resistance against Streptococcus iniae were investigated. The findings revealed that diets physical attributes such as pellet durability index and water stability were remarkably (p < 0.05) varied between experimental diet groups. Furthermore, the test diets were more palatable when FPH was included at 1% and 2%. Fish that were fed with a 2% FPH-treated diet had significantly (p < 0.05) greater growth indices than other treatments. Additionally, their feed utilization was significantly (p < 0.05) improved. The experimental diets and intestinal total bacteria count (TBC) exhibited a rising trend with FPH levels, where the 2% FPH-treated diet recorded the highest TBC. Neutrophil (109/L), lymphocyte (109/L), eosinophil (109/L), and red blood cell(1012/L) counts were significantly (p < 0.05) higher in the 2% FPH-treated group, while the white blood cell (109/L), and basophil (109/L) counts were not influenced by the FPH inclusion. Moreover, the FPH-treated groups displayed lower creatinine, bilirubin, and urea levels than the control. The histological examination demonstrated that themid-intestine of 2% FPH-fed Nile tilapia had an unbroken epithelial wall, more villi with frequent distribution of goblet cells, wider tunica muscularis, and stronger stratum compactum bonding than other treatments. Additionally, this group exhibited more nuclei and erythrocytes and less vacuolar cytoplasm in liver than their counterparts. Nile tilapia that were given a diet containing 2% FPH had significantly (p < 0.05) higher resistance (83.33%) to S. iniae during the bacterial challenge test. A significant (p < 0.05) enhancement in farm economic efficiency was observed in the higher inclusion of FPH in diets. In summary, 2% FPH supplementation in Nile tilapia diets improved their growth performance, feed utilization, health status, disease resistance, and farm economic efficiency.

Evaluation of palmatine as an immunostimulant in diet for genetically improved farmed tilapia (GIFT, Oreochromis niloticus)

Palmatine as a medicinal herbs extract has strong bacteriostatic ability and is a promising source of antibacterial additive. The objective of this study was to assess the feasibility of palmatine as an antibiotic alternative in diet for genetically improved farmed tilapia (GIFT, Oreochromis niloticus). Four experimental diets were formulated with 0, 200, 400, and 800 mg/kg palmatine. Tilapia with consistent size (initial body weight 3.43 ± 0.02 g) were fed the test diets twice daily for ten weeks. Dietary palmatine inclusion regardless of levels unaffected the growth performance and feed efficiency (P > 0.05). However, dietary 200–800 mg/kg palmatine inclusion reduced the levels of total cholesterol and low-density lipoprotein cholesterol as well as the ratios of low-density/high-density lipoprotein cholesterol and aspartate/alanine aminotransferase in serum (P < 0.05), but generally improved the antioxidant-related enzymes activities in intestine, plasma and liver, the immunoglobulin M, complement 3, and complement 4 contents and lysozyme activity in plasma, and the phagocytic activity of macrophages in head kidney. Bacterial challenge test demonstrated that dietary supplementation with 200–800 mg/kg palmatine enhanced the resistance of tilapia to Aeromonas hydrophila, and the relative percentage survival was the highest in fish fed diet with 400 mg/kg palmatine. In conclusion, dietary palmatine supplementation enhanced the antioxidant and innate immune responses as well as the resistance against A. hydrophila without compromising growth performance of tilapia, and the suitable inclusion level of palmatine was 400 mg/kg of diet for tilapia.

HEMATOLOGY OF Osphronemus goramy FED CONTAINING FERMENTED TURI (Sesbania grandiflora) LEAF MEAL and CHALLENGED WITH Aeromonas hydrophila

Turi leaf (Sesbania grandiflora) is a natural ingredient with antibacterial compounds. This research was conducted from April to June 2022 at the Fish Nutrition Laboratory and the Laboratory of Parasites and Fish Diseases, Faculty of Fisheries and Marine, Universitas Riau. This study aimed to obtain the best dose of fermented turi leaves in feed seen from hematology before and after the challenge test with A.hydrophila. The method used in this study is an experimental method using a one-factor Completely Randomised Design (CRD) with five treatment levels, namely Kn: (no treatment), Kp: (no cure and infected with A.hydrophila), P1: (fermented feed containing 15% turi leaves, 85% soy flour), P2: (30% turi leaves, 70% soy flour), and P3: (45% turi leaves, 55% soy flour). Fish were reared for 46 days. The challenge test was conducted on day 32 with A.hydrophila bacteria at a density of 108 CFU/mL, as much as 0.1 mL/head. The results showed that fermented feed contained 45% turi leaves and 55% soybeans (P3). Wheat flour obtained total erythrocytes 2.51x106 cells/mm3, hematocrit 40.33%, hemoglobin 10.40 g/dL, total leukocytes 10.13x104 cells/mm3, phagocytosis activity 21.13%, survival rate 90%, and absolute weight growth 9.52g. Water quality parameters were temperature ranging from 27-300C, pH 5.9-6.2, DO 5.5-5.9 mg/L, and NH3 0.015-0.017 m g/L. Based on the results of the study, it can be concluded that there is an effect of adding fermented turi leaves to feed on the hematology of gouramy before and after the A.hydrophila bacterial challenge test has a significant impact

Effect of dietary inclusion of mannan oligosaccharides on the efficacy of a novel hydrogen peroxide‐inactivated vaccine against Streptococcus agalactiae in Nile tilapia

AbstractMannan oligosaccharides (MOS) have shown to stimulate immune response in different fish species, but the results may appear contradictory and have not been tested in conjunction with vaccination. We hypothesized that dietary MOS supplementation could enhance efficacy and immune responses after immunization with a novel hydrogen peroxide‐inactivated vaccine. Nile Tilapia, Oreochromis niloticus, fingerlings were distributed into four groups (supplemented or not, vaccinated or not) and were used to determine immune and hematological parameters and somatic indexes. For the bacterial challenge and vaccine efficacy test, fish were assigned to five experimental groups. Twenty‐eight days after the feeding trial and vaccination, the groups were challenged intraperitoneally and monitored for 21 days. The relative percent survival of the groups basal diet‐vaccinated and MOS diet‐vaccinated were 98.1% and 100.0%, respectively. The dietary inclusion of MOS after vaccination for 28 days had no influence on vaccine efficacy, which could be explained because of the high efficacy of the vaccine itself. Therefore, we suggest that the contribution of MOS supplementation to immune responses after vaccination in fish would be greater for vaccines with lower efficacy, or when tested for heterologous challenges or for crossed protection.

Aeromonas salmonicida subsp. Masoucida causes an emerging infectious diseases and immune response in red swamp crayfish (Procambarus clarkii)

In this study, the characteristics of a dominant strain wx3 isolated from the tissues of several sick red swamp crayfish were studied, and the immune response of the red swamp crayfish under stress was analyzed. The whole genome analysis of wx3 identified it as Aeromonas salmonicida subsp. Masoucida, which was confirmed using the bacterial challenge test, and is the pathogen that causes red swamp crayfish head rot. The sensitivity of wx3 to a variety of antibiotics was found that wx3 was highly sensitive to 13 antibiotics, but was not sensitive to 4 antibiotics. Comparative transcriptome analysis showed that 811 differentially expressed genes (DEGs) were enriched in the hepatopancreas 48 h after wx3 infection. The KEGG pathway analysis and GO analysis detected differentially expressed immune related genes, including C-type lectin 3 and Hsp22, which were upregulated, and also enriched in immune related pathways, such as the C-type lectin receptor signaling pathway, etc. In conclusion, by analyzing transcriptome, we found that red swamp crayfish infected with wx3 can exert a strong immune response.

Immuno-physiological effects of dietary reishi mushroom powder as a source of beta-glucan on Rohu, Labeo rohita challenged with Aeromonas veronii

Beta-glucans have immense potential to stimulate immune modulation in fish by being injected intramuscularly, supplemented with feed or immersion routes of administration. We studied how supplementing Labeo rohita’s diet with reishi mushroom powder containing beta-glucan influenced immunological function. A supplemented diet containing 10% reishi mushroom powder was administered for 120 days. Afterwards, analyses were conducted on different immunological parameters such as antioxidants, respiratory burst, reactive oxygen species (ROS), alternative complement activity, and serum immunoglobulin, which resulted significant increases (p < 0.05; p < 0.01) for the reishi mushroom-fed immune primed L. rohita. Additionally, analyzing various hematological parameters such as erythrocytes and leukocytes count were assessed to elucidate the immunomodulatory effects, indicating positive effects of dietary reishi mushroom powder on overall fish health. Furthermore, the bacterial challenge-test with 1.92 × 104 CFU/ml intramuscular dose of Aeromonas veronii showed enhanced disease-defending system as total serum protein and lysozyme activity levels accelerated significantly (p < 0.01). Nevertheless, reishi mushroom powder contained with beta-glucan ameliorated the stress indicating parameters like acetylcholinesterase (AChE), serum-glutamic pyruvic transaminase (SGPT) and serum-glutamic oxaloacetic transaminase (SGOT) enzyme activities results suggested the fish’s physiology was unaffected. Therefore, the results indicated that adding dietary reishi mushroom as a source of beta-glucan could significantly boost the immune responses in Rohu.

Isolation, characterization and application of a lytic phage vB_VspM_VS1 against Vibrio splendidus biofilm.

Vibrio splendidus is a common pathogen in the ocean that infects Apostichopus japonicus, Atlantic salmon and Crassostrea gigas, leading to a variety of diseases. In this study, a virulent phage vB_VspM_VS1, which infects V. splendidus, was isolated from aquaculture ponds in Dalian, China, and it belongs to the family Straboviridae in the order Caudoviricetes. vB_VspM_VS1 had an adsorption rate of 96% in 15 min, a latent period of 65 min, and a burst size of 140 ± 6 PFU/cell. The complete genome of phage vB_VspM_VS1 consists of a linear double-stranded DNA that is 248,270 bp in length with an average G + C content of 42.5% and 389 putative protein-coding genes; 116 genes have known functions. There are 4 tail fiber genes in the positive and negative strands of the phage vB_VspM_VS1 genome. The protein domain of the phage vB_VspM_VS1 tail fibers was obtained from the Protein Data Bank and the SMART (http://smart.embl.de) database. Bacterial challenge tests revealed that the growth of V. splendidus HS0 was apparently inhibited (OD600 < 0.01) in 12 h at an MOI of 10. In against biofilms, we also showed that the OD570 value of the vB_VspM_VS1-treated group (MOI = 1) decreased significantly to 0.04 ± 0.01 compared with that of the control group (0.48 ± 0.08) at 24 h. This study characterizes the genome of the phage vB_VspM_VS1 that infects the pathogenic bacterium V. splendidus of A. japonicus.

Therapeutics and prophylactic efficacy of novel lytic Escherichia phage vB_EcoS_PJ16 against multidrug-resistant avian pathogenic E. coli using in vivo study.

Avian pathogenic Escherichia coli (APEC) is the causative agent of avian colibacillosis, which causes significant economic losses to the poultry industry. The growing resistance of bacteria to antibiotics is a major global public health concern. However, there is limited data on the efficacy of phage therapy in effectively controlling and treating APEC infections. In this study, a novel lytic Escherichia phage, vB_EcoS_PJ16, was isolated from poultry farm wastewater and characterized in both in vitro and in vivo conditions. Transmission electron microscopy analysis revealed the presence of an icosahedral head and a long non-contractile tail, classifying the phage under the Caudoviricetes class. Host range determination showed that Escherichia phage vB_EcoS_PJ16 exhibited lytic activity against multiple strains of pathogenic E. coli, while no significant signs of lysis for Klebsiella pneumoniae, Salmonella Typhimurium, Listeria monocytogenes, and Staphylococcus aureus. Biophysical characterization revealed that the isolated phage was sturdy, as it remained viable for up to 300days at temperatures of 30°C, 37°C, and 42°C and for up to 24h at pH 5 to 11, with only minor changes in titer. Kinetic analysis at multiplicity of infection (MOI) 0.1 showed a latency period of about 20min and a burst size of 26.5 phage particles per infected cell for phage vB_EcoS_PJ16. Whole genome sequencing unveiled that the phage vB_EcoS_PJ16 genome consists of a double-stranded linear DNA molecule with 57,756bp and a GC content of 43.58%. The Escherichia phage vB_EcoS_PJ16 genome consisted of 98 predicted putative ORFs, with no transfer RNA identified in the genome. Among these 98 genes, 34 genes were predicted to have known functions. A significant reduction in APEC viability was observed at MOI 100 during in vitro bacterial challenge tests conducted at different MOIs (0.01, 1, and 100). In vivo oral evaluation of the isolated phage to limit E. coli infections in day-old chicks indicated a decrease in mortality within both the therapeutic (20%) and prophylactic (30%) groups, when compared to the control group. The findings of this study contribute to our current knowledge of Escherichia phages and suggest a potentially effective role of phages in the therapeutic and prophylactic control of antibiotic-resistant APEC strains.

Evaluation of Yeast Hydrolysate in a Low-Fishmeal Diet for Whiteleg Shrimp (Litopenaeus vannamei).

An eight-week feeding trial was performed to evaluate the effects of yeast hydrolysate (YH) supplementation in a low-fishmeal diet on the growth, immune responses, intestinal histology and disease resistance of whiteleg shrimp (Litopenaeus vannamei). Five experimental diets were produced by supplementing YH at 0 (CON), 0.5 (YH0.5), 1 (YH1), 2 (YH2) and 4 (YH4) % to a basal diet containing 10% fishmeal and compared with a positive control with 25% fishmeal (FM25). Shrimp with an initial average weight of 0.43 ± 0.005 g (mean ± SD) were stocked in 18 tanks and fed the experimental diets (38% protein and 8% lipid) four times a day. Results showed that shrimp fed the FM25 diet exhibited significantly higher final body weight, weight gain, specific growth rate and protein efficiency ratio than those fed CON, YH0.5, YH1 and YH2 diets (p < 0.05). However, there were no significant differences between shrimp fed the YH4 and FM25 diets (p > 0.05). In addition, there were no significant differences in whole-body proximate composition, hemolymph biochemical parameters and non-specific immune responses among treatments. Intestinal villi length and muscular layer thickness of shrimp fed the YH4 and FM25 diets were significantly higher than the other groups. At the end of the bacterial (Vibrio parahaemolyticus) challenge test, shrimp fed YH4 and FM25 diets showed a significantly higher survival rate than those of shrimp fed CON, YH0.5 and YH1 (p < 0.05). These results suggest that supplementing 4% YH in diet containing 10% fishmeal could beneficially influence growth, intestinal morphology and disease resistance of whiteleg shrimp.

Evaluation of an Organically Modified Clinoptilolite (OMC) and a Multi-Component Mycotoxin Detoxifying Agent (MMDA) on Survival, Growth, Feed Utilization and Disease Resistance of Nile Tilapia (Oreochromis niloticus) Fingerlings Fed with Low Aflatoxin

Mycotoxins have become a serious issue in the animal feed industry and have also affected the aquaculture industry. Mycotoxins can create serious health problems in aquatic and terrestrial animals, and their presence in agricultural products may result in significant economic losses. To reduce the impact of mycotoxins on Nile tilapia fry, two commercially available products—Organically Modified Clinoptilolite (OMC) and multi-component mycotoxin detoxifying agent (MMDA)—were used in this study. Six diets as treatments (T1 = Control (C); T2 = Control + OMC 2 g/kg (OMC); T3 = Control + MMDA 2 g/kg (MMDA); T4 = AFB1 0.5 mg/kg (AF); T5 = AFB1 0.5 mg/kg + 2 g/kg OMC (AFOMC); T6 = AFB1 0.5 mg/kg + MMDA 2 g/kg (AFMMDA)) with similar crude protein levels (35.75 ± 0.35%) were formulated and fed to Nile tilapia fry (1.97 ± 0.1 g) for a period of 84 days. These fish were housed in 18 aquaria (100 L) at a density of 50 fish/aquarium. The results from this study showed that MMDA significantly (p &lt; 0.05) improved the survival of fish by 16% as compared to the control group. Nevertheless, growth parameters were not affected among the treatments. These results also indicated that protein intake was significantly higher in the control and OMC diet (T2) compared to aflatoxin B1-fed tilapia. The protein efficiency ratio (PER) was significantly higher in the AFMMDA as compared to the control and MMDA. A 14-day bacterial challenge test with Aeromonas hydrophila demonstrated that diets containing MMDA or OMC improved survival when AFB1 was present in the diet. Therefore, the supplementation of feed with MMDA or OMC is recommended to ameliorate the negative effects of AFB1 in Nile Tilapia feeds.

Beneficial Effects of Graded Levels of Fish Protein Hydrolysate (FPH) on the Growth Performance, Blood Biochemistry, Liver and Intestinal Health, Economics Efficiency, and Disease Resistance to Aeromonas hydrophila of Pabda (Ompok pabda) Fingerling

Fish protein hydrolysate (FPH) is the enzymatic hydrolysis of protein into smaller peptide and free amino acids, which has recently captured considerable attention as a supplementary ingredient in the aqua-feed industry sector. The present research aimed to observe the physiological, biochemical, and bacteriological study of FPH-treated diets and its effects on growth, hematology, plasma biochemistry, liver and gut histopathology, and resistance to Aeromonas hydrophila infection in Pabda (Ompok pabda). Four experimental diets (35% crude protein) were formulated with graded FPH supplementation (0, 0.5, 1, and 2%). The feed physiological parameters such as expansion ratio, bulk density, water stability, and floatability were not significantly affected by dietary FPH levels (p &gt; 0.05), except for the pellet durability index (PDI). Furthermore, the diets with 1% and 2% FPH were more palatable to fish than other treatment diets. The total bacteria (TB) in fish diets and guts followed an increasing trend with the increase in various levels of FPH in diets. The significantly highest body weight, specific growth rate (SGR), total biomass (TB), survival rate (SR), condition factor (CF), and hepatosomatic index (HSI) were noted in 2% FPH-fed fish when compared with other treatment groups (p &lt; 0.05). The feed intake of fish was significantly increased when increasing the FPH in diets (p &lt; 0.05). The fish fed with a 2% FPH diet had significantly higher neutrophil, monocyte, lymphocyte, red blood cell, and platelet levels (p &lt; 0.05). The blood glucose, creatinine, total protein, and globulin were significantly lower in control fish compared to other treatment groups (p &lt; 0.05). The histopathological observation of mid intestine tissues displayed that 2% of FPH-diet-fed fish had a well-anchored epithelial wall with well-arranged goblet cells, a long villus structure, stratum compactum, and tunica muscularis compared to other treatments of FPH. The inclusion of FPH in diets up to 2% significantly improved the liver health of fish. The fish fed with 2% FPH had a significantly lower cumulative percent mortality (16.67%) against A. hydrophila infection in the bacterial challenge test (p &lt; 0.05). Therefore, the present results suggested that using 2% FPH in the aqua-feed industry improves the growth performance, health status, and disease resistance of Pabda fingerlings in captivity.

Dandelion extract on growth performance, immunity, stress and infection resistance in common carp

In the present study, the effect of supplementation with dandelion extract (DE) in common carp feed. Seven levels of DE supplementation to the basal diet were evaluated, i.e., 0 %, 0.5 %, 1 %, 2 %, 4 %, 7 %, and 10 % (50 % polysaccharide content), for a feeding period of 56 days. The addition of DE to the diet increased weight gain rate, specific growth rate,and protein efficiency ratio of common carp in DE2, DE3, DE4, DE5 and DE6 group. In contrast, it significantly reduced feed conversion ratio. Interestingly, DE supplementation did not have a significant effect on survival rate, condition factor, viscerosomatic index, and hepatosomatic index (P > 0.05). Moreover, DE supplementation improved the content of growth hormone (GH) and insulin-like growth factor (IGF-I) hormones in common carp serum, which was correlated with upregulation of genes coding for these two hormones in hepatopancreas (P < 0.05). Furthermore, DE supplementation increased the contents of total protein, albumin, and globulin in common carp, whilst reduced the contents of cholesterol, triglyceride, and urea nitrogen. Supplementation with DE promoted an increase in high-density lipoprotein cholesterol and a decrease in low density lipoprotein cholesterol contents. DE supplementation increased the activities of alysozyme, alkaline phosphatase, superoxide dismutase, catalase, glutathione peroxidase, and total antioxidant capacity, and the levels of complement 3 and complement 4. Furthermore, the activities of AST and ALT, and the contents of malondialdehyde and reactive oxygen species were reduced. In bacterial challenge tests with Aeromonas hydrophila, the mortality rate of common carp receiving supplementation with DE was lower. Collectively, DE supplementation improve growth performance, immunity, antioxidant capacity, gene expression, and the ability to withstand A. hydrophila infection in common carp. The recommended dosage of DE supplementation for the common carp diet is within the range of 5.42 %.

Effect of Biotronic® Top Liquid Supplementation on the Growth Performance and Disease Resistance of Nile Tilapia (Oreochromis niloticus L.)

The present trial was conducted to evaluate whether Biotronic® Top Liquid (BTL) supplementation would benefit during the nursing of Nile tilapia (Oreochromis niloticus) fry in terms of survival, growth, and disease resistance. Isonitrogenous (22.9±0.2% CP) diets were prepared by supplementing 0.0, 0.5, 1.0, 1.5, 2.0 to 2.5 L/ton of BTL diet i.e. T1 to T6, respectively. Each of the 18 aquaria (100 L) was stocked with 45 fish (16.17±0.40g, Mean±SE) having three replicates per treatment. During the trial, fish biomass increased linearly with the increase in BTL dose i.e. 230g (10.3%) of fish biomass/L of BTL. Results showed that higher dose of BTL/ton of feed resulted in to increase growth rate, with an indication of improved growth beyond the tested level i.e. &gt;2.5 L/ton. Bacterial challenge test using Aeromonas hydrophila showed that the highest BTL dose could maintain average fish survival rate above 65%, which was 25% higher than that of control. Average survival improved linearly i.e. (y)=8.857x+40.317 (R²=0.64) with a nearly 9% increase in survival per liter of BTL supplementation. BTL improved SGR, DWG, and PER by 3.4, 1.6 and 2.1 times, respectively as compared to the control when the fish were challenged by bacteria. Therefore, the dose of 2.5 L/ton of feed is recommended based on the present study.

A high-fat diet alters lipid accumulation and oxidative stress and reduces the disease resistance of overwintering hybrid yellow catfish (Pelteobagrus fulvidraco♀×P. vachelli♂)

This study was carried out to investigate the influence of dietary lipid levels on the growth, immune response, and disease resistance of hybrid yellow catfish (Pelteobagrus fulvidraco♀×P. vachelli♂) during overwintering. Yellow catfish (initial body weight: 49.42 ± 1.33 g) were fed isonitrogenous diets (crude protein 40%) with three lipid levels (low lipid: 8.57%, medium lipid: 12.65%, and high lipid: 16.60%) for five weeks before the overwintering stage, and then all fish were fasted during overwintering. After overwintering, a bacterial challenge test was performed. The results showed that dietary lipid levels had no influence on the growth of hybrid yellow catfish before or after overwintering, but the high lipid (16.60%) diet significantly reduced the survival rate of the fish after bacterial challenge (P < 0.05). Crude whole-body fat content in each treatment after overwintering was significantly lower than that before overwintering. In addition, the liver lipid content significantly increased with increasing dietary lipid levels (P < 0.05). Before overwintering, expression levels of genes related to lipogenesis and lipolysis pathways in liver tissue were down-regulated by the 16.6% lipid diet (P < 0.05). Plasma superoxide dismutase (SOD) activities and malondialdehyde (MDA) contents were enhanced with the increase of dietary lipid level before the challenge test. Plasma SOD activities and MDA contents were significantly decreased in the high lipid group, and plasma cortisol content and lysozyme (LYZ) activity in the 16.60% lipid group were significantly higher than those in the 8.57% lipid group (P < 0.05) at 12-h post bacterial challenge. The mRNA expression levels of toll-like receptor 2 (tlr2) in spleen post-challenge were significantly downregulated compared to pre-challenge (P < 0.05). The transcriptional levels of interleukin 1β (il-1β), tumor necrosis factor α1 (tnfα1), interleukin 10 (il-10), and immunoglobulin M (igm) in spleen or kidney were significantly increased post-challenge compared to pre-challenge, and the relative expression levels of immune-related genes in the high lipid group were greater than those of the low lipid group post-challenge (P < 0.05). The results indicated that high dietary lipid (16.60%) induces oxidative stress and reduces disease resistance of hybrid yellow catfish through a pathway involving regulation of tlr and the inflammatory response during overwintering.

Effects of Lactobacillus pentosus combined with Arthrospira platensis on the growth performance, immune response, and intestinal microbiota of Litopenaeus vannamei

Litopenaeus vannamei is one of the most productive shrimp species in the world. However, shrimp farming is suffering from adverse environmental conditions and disease outbreaks. Typically, Lactobacillus pentosus and Arthrospira platensis are used as substitutes for some antibiotics. In the present study, we assessed the effects of dietary supplements along with living bacteria or cell-free extracts of L. pentosus combined with A. platensis on the growth performance, immune response, intestinal microbiota, and disease resistance of L. vannamei against Vibrio alginolyticus. Shrimp fed L. pentosus live bacteria combined with A. platensis showed the best growth performance and lowest feed conversion rate. The supplementation diet with L. pentosus live bacteria and A. platensis could significantly enhance the trypsin activity in shrimp after the feeding trial. Given the lowest feed conversion rate in shrimp fed L. pentosus live bacteria combined with A. platensis, we reasonably speculated that the decrease in feed conversion rate may be related to the increase in trypsin activity. In addition, dietary cell-free extracts of L. pentosus combined with A. platensis enhanced the expression of immune-related genes after the feeding trial or challenge test. Moreover, results of the bacterial challenge test indicated that the shrimp fed cell-free extracts of L. pentosus combined with A. platensis diet resulted in the highest survival rate, which suggested that cell-free extracts of L. pentosus and A. platensis could improve the disease resistance against V. alginolyticus by up-regulating the expressions of immune-related genes. Dietary L.pentosus or A. platensis, or their combination, reduced the abundance of harmful bacteria, including Proteobacteria in shrimp intestine, which suggested that L. pentosus and A. platensis could improve the growth performance and health of shrimp by regulating the structure of the intestinal microbiota. The findings of this study demonstrated that L. pentosus live bacteria and A. platensis exerted synergistic effects on the growth performance and digestion in shrimp, while cell-free extracts of L. pentosus and A. platensis showed synergistic effects on the immune response and disease resistance of shrimp against V. alginolyticus.

Characterization and genome analysis of a novel Vibrio parahaemolyticus phage vB_VpP_DE17

A novel phage vB_VpP_DE17, which infects Vibrio parahaemolyticus, was isolated from the sewer of the Huangsha aquatic market in Guangzhou. Transmission electron microscopy indicated that DE17 had an icosahedral head (47 ± 2 nm diameter) and a short, non-contractile tail (17 ± 2 nm). The genome of DE17 was a double-stranded linear DNA with a length of 43,397 bp and GC content of 49.23%. In total, 49 putative open reading frames (ORFs) were predicted and could be divided into six modules: DNA metabolism, lysis, packaging, structure, additional function, and hypothetical proteins. Taxonomic analysis revealed that the phage belonging to the genus of Maculvirus, Autographivirinae subfamily, Podoviridae family. DE17 had a short latent period of 5 min with burst size of 80 pfu/cell. Its optimum temperature and pH ranges were 4 °C–50 °C and 5–10, respectively; it was completely inactivated after 20 min of ultraviolet irradiation. No transfer RNA (tRNA), virulence associated, or antibiotic resistance genes were identified. Bacterial challenge test revealed that DE17 had a certain inhibitory effect on V. parahaemolyticus within 6 h. Characterization, genomic analysis and in vitro antibacterial assays of DE17 will further enhance our understanding of phage biology and diversity.