Isolation and characterization of Pseudoalteromonas sp. from fermented Korean food, as an antagonist to Vibrio harveyi

Novel Dietary Approach with Probiotics, Prebiotics, and Synbiotics to Mitigate Antimicrobial Resistance and Subsequent Out Marketplace of Antimicrobial Agents: A Review

Antimicrobial resistance (AMR) is a significant public health concern worldwide. The continuous use and misuse of antimicrobial agents have led to the emergence and spread of resistant strains of bacteria, which can cause severe infections that are difficult to treat. One of the reasons for the constant development of new antimicrobial agents is the need to overcome the resistance that has developed against existing drugs. However, this approach is not sustainable in the long term, as bacteria can quickly develop resistance to new drugs as well. Additionally, the development of new drugs is costly and time-consuming, and there is no guarantee that new drugs will be effective or safe. An alternative approach to combat AMR is to focus on improving the body's natural defenses against infections by using probiotics, prebiotics, and synbiotics, which are helpful to restore and maintain a healthy balance of bacteria in the body. Probiotics are live microorganisms that can be consumed as food or supplements to promote gut health and improve the body's natural defenses against infections. Prebiotics are non-digestible fibers that stimulate the growth of beneficial bacteria in the gut, while synbiotics are a combination of probiotics and prebiotics that work together to improve gut health. By promoting a healthy balance of bacteria in the body, these can help to reduce the risk of infections and the need for antimicrobial agents. Additionally, these approaches are generally safe and well tolerated, and they do not contribute to the development of AMR. In conclusion, the continuous development of new antimicrobial agents is not a sustainable approach to combat AMR. Instead, alternative approaches such as probiotics, prebiotics, and synbiotics should be considered as they can help to promote a healthy balance of bacteria in the body and reduce the need for antibiotics.

Klebsiella pneumoniae Volatile Organic Compounds (VOCs) Protect Artemia salina from Fish Pathogen Aeromonas sp.: A Combined In Vitro, In Vivo, and In Silico Approach

Antibiotic resistance is an alarming threat all over the world, and the biofilm formation efficacy of bacteria is making the situation worse. The antagonistic efficacy of Klebsiella pneumoniae against one of the known fish pathogens, Aeromonas sp., is examined in this study. Moreover, Aeromonas sp.'s biofilm formation ability and in vivo pathogenicity on Artemia salina are also justified here. Firstly, six selected bacterial strains were used to obtain antimicrobial compounds against this pathogenic strain. Among those, Klebsiella pneumoniae, another pathogenic bacterium, surprisingly demonstrated remarkable antagonistic activity against Aeromonas sp. in both in vitro and in vivo assays. The biofilm distrusting potentiality of Klebsiella pneumoniae's cell-free supernatants (CFSs) was likewise found to be around 56%. Furthermore, the volatile compounds of Klebsiella pneumoniae were identified by GC-MS in order to explore compounds with antibacterial efficacy against Aeromonas sp. through an in silico study, where 5'-methylthioadenosine/S-adenosylhomocysteine nucleosidase (MTAN) (PDB: 5B7P) was chosen as a target protein for its unique characteristics and pathogenicity. Several volatile compounds, such as oxime- methoxy-phenyl-, fluoren-9-ol, 3,6-dimethoxy-9-(2-phenylethynyl)-, and 2H-indol-2-one, 1,3-dihydro- showed a strong binding affinity, with free energy of -6.7, -7.1, and -6.4 Kcal/mol, respectively, in complexes with the protein MTAN. Moreover, the root-mean-square deviation, solvent-accessible surface area, radius of gyration, root-mean-square fluctuations, and hydrogen bonds were used to ensure the binding stability of the docked complexes in the atomistic simulation. Thus, Klebsiella pneumoniae and its potential compounds can be employed as an alternative to antibiotics for aquaculture, demonstrating their effectiveness in suppressing Aeromonas sp.

Excess iron supplementation induced hepatopancreas lipolysis, destroyed intestinal function in Pacific white shrimp Litopenaeus vannamei

So far, the adverse effects of excess Fe in shrimp have been ignored for years as it was thought that extra Fe supplementation was not needed in the practical diets. Nowadays, Fe concentration in commercial shrimp feed from feed enterprises could be around 301.34-545.5 mg/kg, which is mainly due to the fish meal containing up to 1500 mg/kg Fe. Therefore, the purpose of this experiment was to investigate the effects of Fe supplementation on the growth performance, tissue Fe deposition, hepatopancreas lipid metabolism, intestinal function in L. vannamei. The results showed that although growth performance was not influenced by the dietary Fe supplementation, excess Fe supplementation (955.00 mg/kg) significantly increased hepatopancreas Fe deposition and induced lipolysis. Moreover, excess Fe supplementation impaired intestinal immune function and disrupted microbiota homeostasis. These findings might provide partial theoretical evidence for the effect of dietary Fe supplementation on physiological metabolism in L. vannamei.

Bioassay-guided isolation and characterization of antibacterial compound from Aspergillus fumigatus HX-1 associated with Clam

This study aimed to identify a symbiotic fungus strain HX-1 with anti-Vibrio harveyi activity and isolate and identify the active compound. The HX-1 strain was identified as Aspergillus fumigatus according to the morphological characteristics and internal transcribed spacer (ITS) sequence analysis. The compound was isolated from the fermentation product of HX-1 strain through ethyl acetate extraction, silica gel and Sephadex LH-20 column chromatography, and semi-preparative HPLC techniques using an antibacterial-guided fractionation method. According to its physicochemical properties and spectral characteristics, the compound was identified as trypacidin having the same anti-V. harveyi activity as streptomycin sulfate, with the minimum inhibitory concentration of 31.25 µg/mL.

Antibacterial activity and action mechanism of questin from marine Aspergillus flavipes HN4-13 against aquatic pathogen Vibrio harveyi

This study investigated the antibacterial activity and mechanism of questin from marine Aspergillus flavipes HN4-13 against aquatic pathogenic Vibrio harveyi. The minimal inhibitory concentration and minimal bactericidal concentration of questin against V. harveyi strain SZ-1 and 1.8690 were determined by Oxford cup and tube dilution methods. The mechanism of action of questin against V. harveyi 1.8690 was investigated by bacterial growth curve analysis, ultraviolet absorption, Mo-Sb-Vc colorimetry, alkaline phosphatase and scanning electron microscopy. Results showed that questin exhibited favourable antibacterial and bactericidal activity against V. harveyi by disrupting the cell wall and membrane, which caused the destruction of permeability and integrity of cell wall and membrane, resulting in the leakage of intracellular biological components and change of cell morphology. This paper is the first to report the mechanism of action of questin against the aquatic pathogen V. harveyi.

Taxonomic annotation errors incorrectly assign the family Pseudoalteromonadaceae to the order Vibrionales in Greengenes: implications for microbial community assessments

Next-generation sequencing has provided powerful tools to conduct microbial ecology studies. Analysis of community composition relies on annotated databases of curated sequences to provide taxonomic assignments; however, these databases occasionally have errors with implications for downstream analyses. Systemic taxonomic errors were discovered in Greengenes database (v13_5 and 13_8) related to orders Vibrionales and Alteromonadales. These orders have family level annotations that were erroneous at least one taxonomic level, e.g., 100% of sequences assigned to the Pseudoalteromonadaceae family were placed improperly in Vibrionales (rather than Alteromonadales) and >20% of these sequences were indeed Vibrio spp. but were improperly assigned to the Pseudoalteromonadaceae family (rather than to Vibrionaceae). Use of this database is common; we identified 68 peer-reviewed papers since 2013 that likely included erroneous annotations specifically associated with Vibrionales and Pseudoalteromonadaceae, with 20 explicitly stating the incorrect taxonomy. Erroneous assignments using these specific versions of Greengenes can lead to incorrect conclusions, especially in marine systems where these taxa are commonly encountered as conditionally rare organisms and potential pathogens.

Optimized production and isolation of antibacterial agent from marine Aspergillus flavipes against Vibrio harveyi

Statistical methodologies, including Plackett-Burman design and Box-Behnken design, were employed to optimize the fermentation conditions for the production of active substances against aquatic pathogen Vibrio harveyi by marine-derived Aspergillus flavipes strain HN4-13. The optimal crucial fermentation values for maximum production of active substances against V. harveyi were obtained as follows: X₁ (peptone) = 0.3%, X₂ (KCl) = 0.25%, and X₃ (inoculum size) = 4.5%. The predicted diameter of inhibitory zone against V. harveyi was 23.39 mm, and the practical value reached 23.71 ± 0.98 mm with a 62.3% increase. Bioassay-guided fractionation resulted in the acquisition of two compounds whose structures were identified as questin (1) and emodin (2). Questin exhibited the same antibacterial activity against V. harveyi as streptomycin (MIC 31.25 µg/mL). This is the first time to report questin as a potential antibacterial agent against aquatic pathogen V. harveyi.

Optimized extraction process and identification of antibacterial substances from Rhubarb against aquatic pathogenic Vibrio harveyi

Response surface optimization was applied for the extraction of antibacterial substances from Rhubarb (ASR) against aquatic pathogenic Vibrio harveyi. Based on the experimental results of single factors, the optimal extraction conditions were determined by Box-Behnken design combined with response surface methodology with conditions: 100% ethanol as extraction solvent, liquid/material ratio of 29 mL/g and extraction temperature at 88 °C for 148 min. The factual value of inhibition zones can reach 21.31 ± 0.95 mm and is not different from the predicted value (21.74 mm), which showed that the response surface methodology applied to the extraction optimization of antibacterial substances from Rhubarb against V. harveyi is feasible. Moreover, the yield of ASR was 30.29 ± 2.27%. Five compounds, namely, aloe-emodin, rhein, emodin, chrysophanol and physcion, were identified in ASR by comparing the HPLC chromatogram of the reference mixtures and the sample. Contents of the five compounds were 0.68 ± 0.02, 0.24 ± 0.05, 0.78 ± 0.07, 6.68 ± 0.97 and 0.58 ± 0.15%, respectively. The minimal inhibitory concentration (MIC) values of ASR, aloe-emodin, rhein, emodin, chrysophanol and physcion were 0.625, 0.125, 0.015, > 1, > 1, and > 1 mg/mL, respectively, which indicated that aloe-emodin and rhein are the main antibacterial compounds of Rhubarb.

Complete Genome Sequence of Pseudoalteromonas piscicida Strain DE2-B, a Bacterium with Broad Inhibitory Activity toward Human and Fish Pathogens

Pseudoalteromonas piscicida strain DE2-B is a halophilic bacterium which has broad inhibitory activity toward vibrios and other human and fish pathogens. We report the first closed genome sequence for this species, which consists of two chromosomes (4,128,210 and 1,188,838 bp). Annotation revealed multiple genes encoding proteases with potential antibacterial properties.

Mechanisms for Pseudoalteromonas piscicida-Induced Killing of Vibrios and Other Bacterial Pathogens

Pseudoalteromonas piscicida is a Gram-negative gammaproteobacterium found in the marine environment. Three strains of pigmented P. piscicida were isolated from seawater and partially characterized by inhibition studies, electron microscopy, and analysis for proteolytic enzymes. Growth inhibition and death occurred around colonies of P. piscicida on lawns of the naturally occurring marine pathogens Vibrio vulnificus, Vibrio parahaemolyticus, Vibrio cholerae, Photobacterium damselae, and Shewanella algae Inhibition also occurred on lawns of Staphylococcus aureus but not on Escherichia coli O157:H7 or Salmonella enterica serovar Typhimurium. Inhibition was not pH associated, but it may have been related to the secretion of a cysteine protease with strong activity, as detected with a synthetic fluorogenic substrate. This diffusible enzyme was secreted from all three P. piscicida strains. Direct overlay of the Pseudoalteromonas colonies with synthetic fluorogenic substrates demonstrated the activity of two aminopeptidase Bs, a trypsin-like serine protease, and enzymes reactive against substrates for cathepsin G-like and caspase 1-like proteases. In seawater cultures, scanning electron microscopy revealed numerous vesicles tethered to the outer surface of P. piscicida and a novel mechanism of direct transfer of these vesicles to V. parahaemolyticus Vesicles digested holes in V. parahaemolyticus cells, while the P. piscicida congregated around the vibrios in a predatory fashion. This transfer of vesicles and vesicle-associated digestion of holes were not observed in other bacteria, suggesting that vesicle binding may be mediated by host-specific receptors. In conclusion, we show two mechanisms by which P. piscicida inhibits and/or kills competing bacteria, involving the secretion of antimicrobial substances and the direct transfer of digestive vesicles to competing bacteria.IMPORTANCEPseudoalteromonas species are widespread in nature and reduce competing microflora by the production of antimicrobial compounds. We isolated three strains of P. piscicida and characterized secreted and cell-associated proteolytic enzymes, which may have antimicrobial properties. We identified a second method by which P. piscicida kills V. parahaemolyticus It involves the direct transfer of apparently lytic vesicles from the surface of the Pseudoalteromonas strains to the surface of Vibrio cells, with subsequent digestion of holes in the Vibrio cell walls. Enzymes associated with these vesicles are likely responsible for the digestion of holes in the cell walls. Pseudoalteromonas piscicida has potential applications in aquaculture and food safety, in control of the formation of biofilms in the environment, and in food processing. These findings may facilitate the probiotic use of P. piscicida to inactivate pathogens and may lead to the isolation of enzymes and other antimicrobial compounds of pharmacological value.

Probiotics in fish and shellfish culture: immunomodulatory and ecophysiological responses

Aquaculture is emerging as one of the most viable and promising enterprises for keeping pace with the surging need for animal protein, providing nutritional and food security to humans, particularly those residing in regions where livestock is relatively scarce. With every step toward intensification of aquaculture practices, there is an increase in the stress level in the animal as well as the environment. Hence, disease outbreak is being increasingly recognized as one of the most important constraints to aquaculture production in many countries, including India. Conventionally, the disease control in aquaculture has relied on the use of chemical compounds and antibiotics. The development of non-antibiotic and environmentally friendly agents is one of the key factors for health management in aquaculture. Consequently, with the emerging need for environmentally friendly aquaculture, the use of alternatives to antibiotic growth promoters in fish nutrition is now widely accepted. In recent years, probiotics have taken center stage and are being used as an unconventional approach that has numerous beneficial effects in fish and shellfish culture: improved activity of gastrointestinal microbiota and enhanced immune status, disease resistance, survival, feed utilization and growth performance. As natural products, probiotics have much potential to increase the efficiency and sustainability of aquaculture production. Therefore, comprehensive research to fully characterize the intestinal microbiota of prominent fish species, mechanisms of action of probiotics and their effects on the intestinal ecosystem, immunity, fish health and performance is reasonable. This review highlights the classifications and applications of probiotics in aquaculture. The review also summarizes the advancement and research highlights of the probiotic status and mode of action, which are of great significance from an ecofriendly, sustainable, intensive aquaculture point of view.