Pathogenecity of Pseudomonas aeruginosa in Oreochromis mossambicus and treatment using lime oil nanoemulsion

Enrofloxacin, Effective Treatment of Pseudomonas aeruginosa and Enterococcus faecalis Infection in Oreochromis niloticus

Enrofloxacin is a broad-spectrum synthetic antimicrobial drug widely used in veterinary medicine. The present study aimed to determine the effective enrofloxacin dose for treating Pseudomonas aeruginosa and Enterococcus faecalis infection in Oreochromis niloticus. P. aeruginosa and E. faecalis isolates were verified using selective differential media and biochemically using the Vitek 2 test. Bacterial isolates were virulent for O. niloticus with LD50 equal to 2.03 × 106 and 2.22 × 107 CFU fish-1 for P. aeruginosa and E. faecalis, respectively. Infected fish suffered from decreased feed intake followed by off-food, tail erosion, darkening of the external body surface, exophthalmia, ascites, and loss of escape reflex. Internally, congested hemorrhagic hepatopancreas with engorged distended gall bladder were dominant. The posterior kidney was congested with enlarged spleen, and empty elementary tract. Pathologically, severe degenerative changes were dominant in the hepatopancreas, posterior kidney, spleen, stomach, and gills of infected fish. Antimicrobial sensitivity test indicated the high susceptibility of P. aeruginosa and E. faecalis to enrofloxacin with MIC estimated at 1 and 0.0625 µg/mL, respectively. Enrofloxacin effectively protected O. niloticus against E. faecalis and P. aeruginosa infection when used with medicated feed at doses of 10 and 20 mg kg-1 body weight.

Characterization of a hemolytic and antibiotic-resistant Pseudomonas aeruginosa strain S3 pathogenic to fish isolated from Mahananda River in India

Virulent strain Pseudomonas aeruginosa isolated from Mahananda River exhibited the highest hemolytic activity and virulence factors and was pathogenic to fish as clinical signs of hemorrhagic spots, loss of scales, and fin erosions were found. S3 was cytotoxic to the human liver cell line (WRL-68) in the trypan blue dye exclusion assay. Genotype characterization using whole genome analysis showed that S3 was similar to P. aeruginosa PAO1. The draft genome sequence had an estimated length of 62,69,783 bp, a GC content of 66.3%, and contained 5916 coding sequences. Eight genes across the genome were predicted to be related to hemolysin action. Antibiotic resistance genes such as class C and class D beta-lactamases, fosA, APH, and catB were detected, along with the strong presence of multiple efflux system genes. This study shows that river water is contaminated by pathogenic P. aeruginosa harboring an array of virulence and antibiotic resistance genes which warrants periodic monitoring to prevent disease outbreaks.

Bioactive Analysis of Antibacterial Efficacy and Antioxidant Potential of Aloe barbadensis Miller Leaf Extracts and Exploration of Secondary Metabolites Using GC-MS Profiling

Aloe barbadensis Miller (ABM) is a traditional medicinal plant all over the world. Numerous studies were conducted to exhibit its medicinal properties and most of them were concentrated on its metabolites against human pathogens. The current research work evaluates the attributes of different polar-based extracts (ethanol, methanol, ethyl acetate, acetone, hexane, and petroleum ether) of dried Aloe barbadensis leaf (ABL) to investigate its phytochemical constituents, antioxidant potential (DPPH, ABTS), phenolic, tannin, flavonoid contents, identification of bioactive compounds, and functional groups by gas chromatography-mass spectrometry (GC-MS) and fourier transform infrared spectroscopy (FT-IR) respectively, and comparing antibacterial efficacy against human pathogens, aquatic bacterial pathogens, and zoonotic bacteria associated with fish and human. The present results showed that the methanolic extract of ABL showed higher antioxidant activity (DPPH-59.73 ± 2.01%; ABTS-74.1 ± 1.29%), total phenolic (10.660 ± 1.242 mg GAE/g), tannin (7.158 ± 0.668 mg TAE/g), and flavonoid content (49.545 ± 1.928 µg QE/g) than that of other solvent extracts. Non-polar solvents hexane and petroleum ether exhibited lesser activity among the extracts. In the case of antibacterial activity, higher inhibition zone was recorded in methanol extract of ABL (25.00 ± 0.70 mm) against Aeromonas salmonicida. Variations in antibacterial activity were observed depending on solvents and extracts. In the current study, polar solvents revealed higher antibacterial activity when compared to the non-polar and the mid-polar solvents. Diverse crucial bioactive compounds were detected in GC-MS analysis. The vital compounds were hexadecanoic acid (30.69%) and 2-pentanone, 4-hydroxy-4-methyl (23.77%) which are responsible for higher antioxidant and antibacterial activity. Similar functional groups were identified in all the solvent extracts of ABL with slight variations in the FT-IR analysis. Polar-based solvent extraction influenced the elution of phytocompounds more than that of the other solvents used in this study. The obtained results suggested that the ABM could be an excellent source for antioxidant and antibacterial activities and can also serve as a potential source of effective bioactive compounds to combat human as well as aquatic pathogens.

Microbial colonization and chemically influenced selective enrichment of bacterial pathogens on polycarbonate plastic

Plastic pollution in aquatic environments poses significant concerns due to its potential to serve as a refuge for aquatic pathogens. However, the role of plastic surfaces and microbial biofilm interfaces in facilitating pathogen development remains poorly understood. In this study, a microcosm setup was employed to investigate the interactions between plastics and the microbial community and examine the differences in bacterial community composition and potential pathogen occurrences between the plastisphere-biofilm and surrounding seawater. Community composition analysis combined with SEM observations over time indicated that biofilm extracellular polymeric substance formation over 14 days had a link with the relative abundance and succession patterns of pathogen taxa. Colony clusters were observed on biofilms from day 7 and coincided with higher bacterial pathogen dominance. On day 14, pathogen abundance overall decreased with a potentially degrading biofilm. Pseudomonas and Pseudoalteromonas were the dominant potential pathogen groups observed in the microcosm. When further subjected to chemical treatment as an imposed environmental stress over time, biofilm-associated Psuedoalteromonas sharply increased in abundance after three days of exposure, but quickly diminished by 14 days in favor of genera such as Acinetobacter, Pseudomonas, and Staphylococcus. These results suggest that environmental plastisphere-biofilms can promote the early selection, enrichment, and spread of pathogenic bacteria in the aquatic environment and could be later worsened under chemical and long-term pressure. This study provided new insights into the succession of pathogens in plastisphere biofilms, contributing to the understanding of pathogen risks involved in emerging plastisphere biofilms in light of global plastic pollution.

Citrus essential oils - Based nano-emulsions: Functional properties and potential applications

Citrus essential oils are natural products with various bioactive properties (e.g., antimicrobial, antioxidant, and antimutagenic activities), that are generally recognized as safe (GRAS) by Food and Drug Administration (FDA) to be used as flavorings and food additives. Nonetheless, due to their high volatility, low solubility in water, low thermal stability, susceptibility to oxidation, and strong flavor, their applications in the food industry are limited. Nanotechnology allows the incorporation of citrus essential oils into nano-emulsion systems, thus protecting them from the deterioration caused by external factors and maintaining or even improving their functional properties. This study aims to summarize the antioxidant, antimicrobial, and antimutagenic effects of the nano-emulsions based on essential oils from citrus peels with emphasis on their mechanisms of action and potential applications in, e.g., foods, pharmaceuticals, and cosmetics.

Alginate coated biogenic silver nanoparticles for the treatment of Pseudomonas infections in rainbow trout

Pseudomonas species are among the main pathogens causing rainbow trout infections. The present study provides a simple, green, sustainable, and rapid technique to synthesize of biogenic alginate-capped silver nanoparticles (Alg-Ag NPs) suitable for the treatment of Pseudomonas infections. It has been shown that the mechanism (aggregative or autocatalytic) of Alg-Ag NPs formation depended on Alg concentration and the heating approach used. The rate constants and activation energy were calculated. Alg-Ag NPs were characterized by UV-Vis, FTIR, XRD, TEM, AFM, XPS, and DLS. The optimal conditions for the fabrication of spherically-shaped (17-19 nm) and negatively-charged (zeta-potential <-50 mV) Alg-Ag NPs, which are stable during 9 months, included hot-plate assisted synthesis at 100 °C in diluted (1 mg/mL) Alg solutions. In vitro studies showed that Alg-Ag NPs exhibited prominent antimicrobial activity against collection Pseudomonas strains (inhibition zones ranged from 9.0 ± 1.0 to 19.0 ± 1.0 mm), with no significant loss of antibacterial efficacy after 9 months of storage. AFM analysis confirmed that the antibacterial effect of Alg-Ag NPs dealt with the direct nanomechanical disrupting of bacterial cells. The ability of Alg-Ag NPs to inhibit the growth of virulent P.aeruginosa, P.fluorescens and P. putida strains isolated from infected rainbow trout was evaluated. All tested strains were susceptible to Alg(10)-Ag NPs, while Alg(1)-Ag NPs demonstrated a limited strain-specific antibacterial effect. The obtained data displayed the prospects for the application of biogenic Alg-Ag NPs to create novel delivery systems for combating Pseudomonas infections in rainbow trout.

Riverine pollution influences the intraspecific variation in the gut microbiome of an invasive fish, Cyprinus carpio (Linn., 1758)

Humans are significantly impacting riverine systems worldwide, prompting us to investigate the effects of water pollution on the gut microbiome of Cyprinus carpio (common carp). Using 16S rRNA gene sequencing, we compared the gut microbiomes of common carp from two sites along river Yamuna with different pollution levels. Water pollution significantly altered the fish gut microbiome structure and microbial composition. Proteobacteria dominated in both sampling sites, while Bacteroidota prevailed in polluted water samples, indicating sewage and fecal contamination. Less polluted samples exhibited Verrucomicrobiae and Planctomycetes, negatively correlated with pollution levels. The polluted site had higher prevalence of potentially pathogenic and heavy metal-resistant bacteria, as well as microbial communities associated with wastewater treatment systems. Functional prediction highlighted the significant role of the gut microbiome in digestion and metabolism, with active enzymes for breaking down various organic substances. Biosynthetic pathways for leucine, valine, and isoleucine were present in both sites, known to be involved fish immunity. The host maintained a stable and diverse bacterial consortium, while microbial diversity became more specialized due to human activities, adapting to anthropogenic stress and selection pressures.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13205-023-03747-0.

Indole-3-acetic acid impacts biofilm formation and virulence production of Pseudomonas aeruginosa

Bacterial pathogenesis involves complex mechanisms contributing to virulence and persistence of infections. Understanding the multifactorial nature of bacterial infections is crucial for developing effective interventions. The present study investigated the efficacy of indole-3-acetic acid (IAA) against Pseudomonas aeruginosa with various end points including antibacterial activity, minimum inhibitory concentration (MIC), virulence factor production, biofilm inhibition, bacterial cell detachment, and viability assays. Results showed significant biofilm inhibition, bacterial cell detachment, and modest effects on bacterial viability. Microscopic analysis confirmed the disintegrated biofilm matrix, supporting the inhibitory effect of IAA. Additionally, molecular docking studies revealed potential mechanisms of action through active bond interactions between IAA and virulence proteins. These findings highlight IAA as an effective antibiofilm agent against P. aeruginosa.

Identifying Bacteria with Public Health Significance from Farmed Nile Tilapia (Oreochromis niloticus), Zambia

Zambia has seen rapid development in aquaculture, and in recent years, the industry has experienced disease outbreaks where fish have increasingly become a potential contributor to emerging bacterial zoonotic diseases. The aim of this study was to identify bacterial pathogens with zoonotic potential in apparently healthy fish and water from their habitat. A total of sixty-three fish were sampled, and fifty-nine water samples were collected from the habitats of these fish. Bacteria were cultured from the internal organs of fish and water, and these were identified through standard bacteriological methods comprising morphological characterization, Gram-staining, and a panel of biochemical tests. The following bacterial pathogens with zoonotic potential were identified at a farm prevalence of Aeromonas (13.2%), Bacillus (2.1%), Clostridium (2.1%), Escherichia coli (0.7%), Klebsiella (6.9%), Lactococcus (2.1%), Listeria (0.7%), Staphylococcus (18.1%), and Streptococcus (0.7). Other bacteria with varying significance as fish pathogens identified included Acinetobacter (2.1%), Aequorivita (1.4%), Aerococcus (1.4%), Bordetella (2.1%), Carnobacterium (10.4%), Citrobacter (3.5%), Corynebacterium (1.4%), Dermatophilus (1.4%), Enterococcus (2.1%), Flavobacterium (4.2%), Micrococcus (6.9%), Planococcus (1.4%), Proteus (1.4%), Pseudomonas (6.3%), Rhodococcus (1.4%), Shewanella (1.4%), Streptococcus (0.7%), and Vagococcus (0.7%). The current study provides baseline information for future reference and the implementation of public health guidelines with regard to potential zoonotic diseases in fish.

Evaluation of Phytochemical Screening, Pigment Content, In Vitro Antioxidant, Antibacterial Potential and GC-MS Metabolite Profiling of Green Seaweed Caulerpa racemosa

Exploration of seaweeds to unravel their bioactive metabolites from the perspective of wider applications gained substantial importance. The present study was performed to investigate the total phenolic, flavonoid, tannin content, antioxidant activity and antibacterial potential of various solvent extracts of green seaweed Caulerpa racemosa. The methanolic extract showed higher phenolic (11.99 ± 0.48 mg gallic acid equivalents/g), tannin (18.59 ± 0.54 mg tannic acid equivalents/g) and flavonoid (33.17 ± 0.76 mg quercetin equivalents/g) content than other extracts. Antioxidant activity was determined by using 2,2-diphenylpicrylhydrazyl (DPPH) and 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) assay with different concentrations of C. racemosa extracts. The methanolic extract showed higher scavenging potential in both the DPPH and ABTS activity with the inhibition value of 54.21 ± 1.39% and 76.62 ± 1.08%, respectively. Bioactive profiling was also identified by using Gas chromatography-mass spectrometry (GC-MS) and Fourier transform infrared (FT-IR) techniques. These studies revealed the presence of valuable bioactive compounds in C. racemosa extracts and these compounds might be responsible for antimicrobial, antioxidant, anticancer and anti-mutagenic properties. Major compounds identified in GC-MS were 3,7,11,15-Tetramethyl-2-hexadecen-1-ol, 3-hexadecene and Phthalic acid. In terms of antibacterial activity, C. racemosa has promising antibacterial potential against aquatic pathogens Aeromonas hydrophila, Aeromonas veronii and Aeromonas salmonicida. Further evaluation studies focusing aquatic related aspects would reveal the novel bioproperties and applications of C. racemosa.

Tentative Epidemiological Cut-Off Values and Distribution of Resistance Genes in Aquatic Pseudomonas Species Isolated from Rainbow Trout

Epidemiological cut-off value (ECV) analysis for commonly used antimicrobials in aquaculture have not been established for many aquatic pathogens, including Pseudomonas. This study was the first to examine the categorization of 92 aquatic Pseudomonas isolates by calculating seven antimicrobials ECVs using two analytical methods: normalized resistance interpretation and ECOFFinder. Pseudomonas spp. isolates had decreased sensitivity to all antimicrobials examined except for doxycycline and ciprofloxacin. The PCR analysis of the 91 isolates of Pseudomonas spp. detected the tetracycline genes are predominant with the count of 41 genes, including tetA, tetC, tetD, tetM, tetS and tetH, following sulfonamide genes are in 21 isolates including sul1 and sul2, floR gene in 15 isolates and ermA gene in three isolates. Our findings provide an understanding of the antimicrobial categorization of Pseudomonas species, which are significant groups, subgroups, and species for aquaculture due to insufficiently defined breakpoints or cut-off values reported in CLSI and/or EUCAST.

Inhibition of microbial pathogens in farmed fish

Aquaculture, also known as aqua farming, is defined as farming fish, crustaceans, mollusks, aquatic plants, algae, and other marine organisms. It includes cultivating fresh- and saltwater populations under controlled conditions compared to commercial fishing or wild fish harvesting. Worldwide, carp, salmon, tilapia, and catfish are the most common fish species used in fish farming in descending order. Disinfectants prevent and/or treat different infections in aquatic animals. The current review indicates the uses of different disinfectants against some important pathogens in aquaculture, with particular reference to tilapia (Oreochromis niloticus) farming. A single review cannot cover all aspects of disinfection throughout aquaculture, so the procedures and principles of disinfection in tilapia farming/aquaculture have been chosen for illustration purposes.

Antibiotic resistance's Genotypic and Phenotypic Characteristics and the Frequency of Virulence Factors in P. aeruginosa Isolates Isolated from Water Samples in Iran

Pseudomonas aeruginosa is a pathogenic bacterium that can contaminate water. In this study, 430 water samples were evaluated for P. aeruginosa, antibiotic resistance, and the abundance of virulence factors. P. aeruginosa was isolated from 28 (6.51%) water samples. Among the types of water, well and spring water showed the highest P. aeruginosa with, respectively, 20 (15.6%) and 5 (8.06%) positive samples per type of samples. Drinking water and mineral water showed minor contamination with P. aeruginosa. The prevalence of antibiotic resistance against meropenem, imipenem, erythromycin, gentamicin, chloramphenicol, and enrofloxacin was zero. The lowest and highest prevalence of antibiotic resistance was observed in drinking water and well water, respectively. The most abundant genes encoding antibiotic resistance in the P. aeruginosa were blaTEM , blaCTX-M , and blaSHV . This study also showed that the most abundant virulence genes in the Pseudomonas aeruginosa strain isolated from water were algD (15 = 3.49%), lasB (11 = 2.56%), toxA (10 = 2.32%), and exoS (7 = 1.63%). This study suggests that water may be a source of P. aeruginosa and contribute to releasing resistance genes through the food chain. Cross-contamination is the water transfer process that can cause contamination with P. aeruginosa in water. Therefore, hygienic principles can be effective in reducing water contamination.

Metagenomic insights to understand the role of polluted river Yamuna in shaping the gut microbial communities of two invasive fish species

The gastrointestinal microbial community plays a crucial role in host health, immunity, protection, development and provides nutrients to the host. The rising human-induced pollution and heavy metal contamination in all aquatic systems globally has led us to explore the gut microbial diversity of two exotic invasive fish Cyprinus carpio (Linnaeus, 1858) and Oreochromis niloticus (Linnaeus,1857) from river Yamuna, India. These fishes are aquatic bioindicators with high demographic resilience. Exploring these associations would pave the way for addressing problems that inhabitant fishes are facing due to the increasing pollution load in the River Yamuna. Based on 16S rRNA gene amplicon sequencing, our results deliver comparative information on the gut microbiome of these fishes and highlight connotations between the microbiome of gut and water samples. The gut of C. carpio and O. niloticus was dominated by phyla Proteobacteria whereas Bacteroidetes dominated the water sample. Microbial communities showed predicted roles such as pathogenicity (Escherichia-Shigella, Aeromonas veronii, Vibrio cholerae, Streptococcus iniae, Flavobacterium columnare, Klebsiella pneumoniae, Mycobacterium sp.), probiotic applications (Bacillus velezensis, Lactobacillus plantarum, Enterococcus faecalis, Bifidobacterium longum, Lactococcus lactis, Leuconostoc falkenbergense) and involvement in sewage and organic matter decomposition (Nitrosomonas sp., Methanosaeta harundinacea, Dechloromonas agitata, Thauera humireducens, Zoogloea ramigera). Heavy metal degrading members (Leucobacter chromiireducens, Pseudomonas fluorescens, P. aeruginosa, Klebsiella pneumoniae, and Micrococcus luteus) were detected in gut microbiome samples thus supporting the notion that fish shapes its gut microbiota with changing ecology. Functional profiling showed that microbial communities are specialized in metabolic functions thus reflecting the dietary profile of these invasive fishes.

Dietary Parsley Seed Mitigates Methomyl-Induced Impaired Growth Performance, Hemato-Immune Suppression, Oxidative Stress, Hepato-Renal Damage, and Pseudomonas aeruginosa Susceptibility in Oreochromis niloticus

The present experiment investigated the potential protective role of parsley (Petroselinum crispum) seed meal (PSM) in alleviating methomyl (MET)-adverse impacts on growth, whole-body composition, hematological indicators, hepatorenal function, immune response, oxidative status, and disease resistance to Pseudomonas aeruginosa. For this purpose, 225 healthy Nile tilapia (Oreochromis niloticus) were allotted into five groups (45 fish/group in triplicate). One group was reared in clean water and fed a non-supplemented basal diet, while the other groups were exposed to 20.39 μg L^-1 MET and fed a non-fortified basal diet or basal diets supplemented with 0.5, 1.0, or 2.0% of PSM for 60 days. The obtained data revealed significantly lower weight gain, feed intake, and specific growth rate, but higher feed conversion ratio and decreases in crude protein, lipid, and ash contents in the MET-exposed fish. Anemia, leukopenia, lymphocytopenia, and esonipenia were also obvious. Furthermore, MET-exposed fish had significantly higher serum levels of hepatic enzymes and renal damage products. Nevertheless, there was a significant depletion of enzymatic and non-enzymatic antioxidants and increased malondialdehyde, myeloperoxidase, and tumor necrosis factor-α levels in MET-exposed fish. The MET exposure significantly depressed lysozyme activity, nitric oxide, complement3, acetylcholinesterase activity, total proteins, globulin, and albumin levels in O. niloticus serum. Furthermore, pathological alterations in the liver and kidney were noted. The relative percentage of survival rate in MET-exposed fish was dramatically reduced on day 14 post-challenge with P. aeruginosa. The inclusion of PSM, on the other hand, greatly alleviated most of the MET-related negative effects. Taken together, the dietary intervention with PSM has a promising role in alleviating MET-deleterious impacts, rendering parsley seeds a viable aqua feed additive for O. niloticus.

Rapid detection of microorganisms in a fish infection microfluidics platform

Inadequate access to clean water is detrimental to human health and aquatic industries. Waterborne pathogens can survive prolonged periods in aquatic bodies, infect commercially important seafood, and resist water disinfection, resulting in human infections. Environmental agencies and research laboratories require a relevant, portable, and cost-effective platform to monitor microbial pathogens and assess their risk of infection on a large scale. Advances in microfluidics enable better control and higher precision than traditional culture-based pathogen monitoring approaches. We demonstrated a rapid, high-throughput fish-based teleost (fish)-microbe (TelM) microfluidic-based device that simultaneously monitors waterborne pathogens in contaminated waters and assesses their infection potential under well-defined settings. A chamber-associated port allows direct access to the animal, while the transparency of the TelM platform enables clear observation of sensor readouts. As proof-of-concept, we established a wound infection model using Pseudomonas aeruginosa-contaminated water in the TelM platform, where bacteria formed biofilms on the wound and secreted a biofilm metabolite, pyoverdine. Pyoverdine was used as fluorescent sensor to correlate P. aeruginosa contamination to infection. The TelM platform was validated with environmental waterborne microbes from marine samples. Overall, the TelM platform can be readily applied to assess microbial and chemical risk in aquatic bodies in resource-constrained settings.

Marine fungal metabolites as a source of drug leads against aquatic pathogens

Aquatic pathogens, including Vibrio, Edwardsiella, Pseudomonas, and Aeromonas, which could result in bacterial diseases to aquaculture, have seriously threatened the world aquaculture production. Marine-derived fungi, which could produce novel secondary metabolites with significant antibacterial activity, may be an important source for finding effective agents against aquatic pathogens. In this review, a systematically overview of the harm of several aquatic pathogens, and 134 antibacterial secondary metabolites against aquatic pathogens from 13 genera of marine-derived fungi, were summarized and concluded. The aim of this review is to find out the relationships between activity and structural type, between bioactive compounds and their hosts, and so on. Altogether, 95 references published during 1997-2021 were cited. KEY POINTS: •Aquatic pathogens, which could result in bacterial diseases to aquaculture, were described. •Marine fungal metabolites with activities against aquatic pathogens were summarized. •The distributions of these bioactive marine fungal metabolites were analyzed.

Molecular properties and ligand specificity of zebrafish intelectin-2

Intelectins are immune lectins expressed in chordates, including several fish species, in which intelectins are known to be upregulated upon infection. However, the basic biochemical properties and bacteria binding specificities of several fish intelectins are not well studied. We focus our investigation on zebrafish intelectin-2 (DrIntL-2) that is predominantly expressed in the gastrointestinal tract. The disulfide-linked oligomeric state and the cysteine responsible for intermolecular disulfide bonds are identified. DrIntL-2 is a globular particle of around 30 nm. In addition to the typical exocyclic 1,2-diol ligands, DrIntL-2 binds β-1,3-glucan and recognizes Salmonella typhimurium and Pseudomonas aeruginosa. This investigation not only shed light on the fish innate immunity that will be essential for the aquaculture industry, but will also provide a foundation for further application of DrIntL-2 in bacteria detection and identification.

Growth hormone secretagogue peptide-6 enhances oreochromicins transcription and antimicrobial activity in tilapia (Oreochromis sp.)

Growth Hormone-Releasing Peptide 6 (GHRP-6) (His-(D-Trp)-Ala-Trp-(D-Phe)-Lys-NH2) is an agonist of the growth hormone secretagogue receptor. GHRP-6 mimics the effect of ghrelin. The present study focuses on the immunomodulatory effects of GHRP-6 in tilapia with and without the presence of Pseudomonas aeruginosa infection. GHRP-6 up-regulated the transcription levels of three piscidin-like antimicrobial peptides (Oreochromicins I, II, and III) and granzyme in a tissue-dependent manner. Antimicrobial activity stimulation in serum (lysozyme and anti-protease activity) was also confirmed. Besides, GHRP-6 enhanced the in vitro antimicrobial activity against P. aeruginosa in tilapia gills mucus and serum samples and decreased the bacterial load in vivo after infection with this Gram-negative bacterium. Our results evidenced, for the first time, a direct link between a growth hormone secretagogue ghrelin mimetic in fish and the enhancement of antimicrobial peptides transcription, which suggests that this secretagogue is capable to lead the activation of microbicidal activity in tilapia. Thus, these results open new possibilities for GHRP-6 application in aquaculture to stimulate the teleost immune system as an alternative treatment against opportunistic bacteria.

Purification and characterization of bioactive compounds extracted from Suaeda maritima leaf and its impact on pathogenicity of Pseudomonas aeruginosa in Catla catla fingerlings

Incidence of various dreadful microbial infections and the development of antibiotic resistance by infection causative microbes are the main reasons for reducing aquaculture productivity. Hence, there is an immense need for the discovery of alternative and efficient treatment for quick recovery of diseased fishes. In the present study, Suaeda maritima leaf extracts (hexane, diethyl ether, ethanol, and water) were screened for in vitro and in vivo antibacterial and antioxidant activities. Out of all the four extracts, ethanolic extract showed highest antibacterial activity against S. aureus (4.9 ± 1.3 mm), B. subtilis (1.6 ± 0.3 mm), K. pneumoniae (4.2 ± 1.8 mm), and P. aeruginosa (4.1 ± 1.2 mm). Similarly, antioxidant activity was also higher for ethanolic extract (500 µg/mL) based on DPPH radical scavenging ability (71.6 ± 1.4%) and reducing potential (149 μg/mL) assays. Further, ethanolic extract was purified consecutively via column chromatography and preparative TLC where an active fraction was selected based on highest antibacterial (10.1 ± 1.4 mm) and antioxidant properties (82.3 ± 2.8%). Active fraction was loaded onto mass spectroscopy and identified the presence of four active constituents such as 1,2,9,10-tetramethoxy-6-methyl-5,6,6a,7-tetrahydro-4H-dibenzo[de,g]quinolin-3-yl) methanol; 3',7-Dimethoxy-3-hydroxyflavone; Saponin and (19R)9acetyl19hydroxy10,14dimethyl20oxopentacyclo[11.8.0.0 < 2,10 > .0 < 4,9 > .0 < 14,19 >]henicos-17-yl-acetate. Besides, in vivo studies were conducted on Catla catla fingerlings infected with P. aeruginosa under laboratory conditions. The fingerlings were segregated into 5 groups, among which group 4 and 5 were treated with crude and purified extracts. Both the extracts were efficient in treating infected fingerlings and recorded 100% survival rate which is even better than group-3 treated with a synthetic antibiotic (77%). Hence, S. maritima leaf extract can be considered as a possible alternative medicine in aquaculture.

Ecotoxicological assessment and dermal layer interactions of nanoparticle and its routes of penetrations

Our review focused on nanomaterials-based toxicity evaluation and its exposure to the human and aquatic animals when it was leached and contaminated in the environment. Ecotoxicological assessment and its mechanism mainly affect the skin covering layers and its preventive barriers that protect the foreign particles' skin. Nanoscale materials are essential in the medical field, especially in biomedical and commercial applications such as nanomedicine and drug delivery, mainly in therapeutic treatments. However, various commercial formulations of pharmaceutical drugs are manufactured through a series of clinical trials. The role of such drugs and their metabolites has not met the requirement of an individual's need at the early stage of the treatments except few drugs and medicines with minimal or no side effects. Therefore, biology and medicines are taken up the advantages of nano scaled drugs and formulations for the treatment of various diseases. The present study identifies and analyses the different nanoparticles and their chemical components on the skin and their effects due to penetration. There are advantageous factors available to facilitate positive and negative contact between dermal layers. It creates a new agenda for an established application that is mainly based on skin diseases.

Activity profile of innate immune-related enzymes and bactericidal of freshwater fish epidermal mucus extract at different pH

The epidermal mucus of fish performs diverse functions from prevention of mechanical abrasion to limit pathogen invasions. The current experiment was designed to extract skin mucus proteins of three freshwater fish, i.e. common carp (Cyprinus carpio), mrigal (Cirrhinus mrigala) and rohu (Labeo rohita) with organic solvent (methanol) and dissolve in different pH of Tris-HCl buffers to examine the significance of pH in the solubilisation of skin mucus proteins. The protein profiles of different pH solubilised methanol fish skin mucus extracts were determined by SDS-PAGE. The non-specific immune enzymes, alkaline phosphatase, lysozyme and protease of fish skin mucus were compared and this present study demonstrated that these enzymes differed in their activity depending on pH buffers. The higher lysozyme and protease activity were observed at the pH of 8.0 and higher alkaline phosphatase activity in the pH 9.0 of C. mrigala fish skin mucus methanol extract. In addition, the bactericidal activity was evaluated against the pathogens Proteus vulgaris and Pseudomonas aeruginosa. The pH 8.0 of C. mrigala skin mucus extract revealed better bactericidal activity than other fish species mucus pH buffers against both P. vulgaris and P. aeruginosa. In the case of protein profile from SDS-PAGE, based on pH buffers and the solubilisation of proteins, differences in the resolution of bands were observed. The higher alkaline pH of 9.0 showed smeared gel bands in all the three fish skin mucus methanol extract. The present study suggests that methanol extracted C. mrigala fish skin mucus at pH 8.0 showed better innate immune enzymes and bactericidal activity. The additional examinations of C. mrigala skin mucus methanol extract in this pH aids in identifying novel bioactive molecules. This is the study of proteome of three fish species skin mucus in the effect of pH. Further analyses are required to evaluate proteins present in fish skin mucus extracted with methanol and the influence of pH on protein solubility. These findings could be helpful in exploring natural alternatives to antibiotics in aquaculture industry against infectious pathogens.

Survival and gene expression responses in immune challenged larval lake sturgeon

Larval lake sturgeon, Acipenser fulvescens, reared in hatcheries for stock enhancement of wild populations may be susceptible to early opportunistic bacterial infection. Thus, we examined survival and whole-body mRNA expression of both stress- and immune-related genes (MyD88, IL-1β, StAR, GR1, and HSP70) in 30 days post fertilization larval lake sturgeon following immune challenge with lipopolysaccharides (LPS). Larval sturgeon were exposed to 0, 25, 50, 100, 150, and 200 μg ml^-1 LPS and sampled after 30 min, 4 h, and 48 h. Mortality was zero in 0 and 25 μg ml^-1 LPS; 37.5% in 50 μg ml^-1 LPS and 100% in the higher concentrations. Expression of MyD88 and StAR mRNA were positively correlated and increased with time in the 50 μg ml^-1 LPS treatment. There was an influence of both treatment and time on IL-1β mRNA, with expression 10-fold higher than controls after 4 h. Expression of HSP70 mRNA was suppressed within 30 min of 50 μg ml^-1 LPS exposure and remained so throughout the time course. Correlated mRNA expression of GR1 with MyD88, StAR and IL-1β suggests a potential relationship between the innate immune and glucocorticoid responses of larval lake sturgeon during this early developmental stage. Data presented suggest that larval lake sturgeon largely responded with predicted changes in gene expression of immune related and stress response genes following LPS challenge. This study provides a foundation for future research examining the effects of hatchery and naturally occurring stressors on the immune responses of larval lake sturgeon.

Antibacterial activity in secondary metabolite extracts of heterotrophic bacteria against Vibrio alginolyticus, Aeromonas hydrophila, and Pseudomonas aeruginosa

Background: Disease causing bacteria such as Vibrio alginolyticus, Aeromonas hydrophila, and Pseudomonas aeruginosa present a problem for fish farming. Treatment to remove them are generally carried out using antibiotics which have side effects on fish, the environment and humans. However, the use of antibacterial compounds derived from heterotrophic bacteria serve as a good alternative for antibiotics. Therefore, this study aimed to explore antibacterial activity in the secondary metabolite extracts of heterotrophic bacteria against Vibrio alginolyticus, Aeromonas hydrophila, and Pseudomonas aeruginosa. Methods: Heterotrophic bacteria namely Bacillus sp. JS04 MT102913.1, Bacillus toyonensis JS08 MT102920.1, Bacillus cereus JS10 MT102922.1, Bacillus sp. JS11 MT102923.1, Pseudoalteromonas sp. JS19 MT102924.1, Bacillus cereus JS22 MT102926.1, and Bacillus sp. strain JS25 MT102927.1 were used in this study. The sequences of these bacteria have been deposited and are available from NCBI GenBank. Each heterotrophic bacterium was cultured on 6L nutrient broth for 8 days, and extracts produced using ethyl acetate to obtain their secondary metabolites. These extracts were tested for their phytochemical contents using FT-IR and also tested for their inhibitory property in pathogenic bacteria by agar diffusion method. Results: Phytochemical test results showed that the seven heterotrophic bacterial isolates produced terpenoid compounds. Based on the inhibitory test, the secondary metabolite extracts from Bacillus sp strain JS04 had the highest inhibitory effect on the growth of pathogenic bacteria namely, V. alginolyticus (17.5 mm), A. hydrophila (16.8 mm), and P. aeruginosa (17.3 mm). Conclusion: It was concluded that the secondary metabolite extracts of heterotrophic bacteria inhibit the growth of V. alginolyticus, A. hydrophila, and P. aeruginosa.

Lipid-based nano delivery of antimicrobials to control food-borne bacteria

Direct application of antibacterial agents into foods gives limited advantages because bioactive ingredients may be partially inactivated, neutralized, or easily diffused when contacting with the food matrix. Hence, the aim of this study is to investigate the application of lipid-based nanocarriers as delivery systems for antibacterial ingredients. In this regard, several types of these carriers such as nanoliposomes, nanoemulsions, solid lipid nanoparticles (SLNs), and nanostructured lipid carriers (NLCs) are explored. This study seeks to cover the important challenges of lipid-based nanocarriers including structures and characteristics, properties, production methods, advantages and drawbacks, and their applications to encapsulate antibacterial compounds effectively, particularly in food systems. However, for more scrutiny inspection of the functionality of lipid-based nanocarriers, we have gathered and discussed the studies related to the antibiotic-loaded lipid-based nanoparticles. Also, the role of such nanocarriers in active packaging systems when combining with edible coatings or films is discussed.

Characterization of a bacteriophage with broad host range against strains of Pseudomonas aeruginosa isolated from domestic animals

Background

Pseudomonas aeruginosa is an opportunistic pathogen and one of the leading causes of nosocomial infections. Moreover, the species can cause severe infections in cystic fibrosis patients, in burnt victims and cause disease in domestic animals. The control of these infections is often difficult due to its vast repertoire of mechanisms for antibiotic resistance. Phage therapy investigation with P. aeruginosa bacteriophages has aimed mainly the control of human diseases. In the present work, we have isolated and characterized a new bacteriophage, named Pseudomonas phage BrSP1, and investigated its host range against 36 P. aeruginosa strains isolated from diseased animals and against P. aeruginosa ATCC strain 27853.

Results

We have isolated a Pseudomonas aeruginosa phage from sewage. We named this virus Pseudomonas phage BrSP1. Our electron microscopy analysis showed that phage BrSP1 had a long tail structure found in members of the order Caudovirales. “In vitro” biological assays demonstrated that phage BrSP1 was capable of maintaining the P. aeruginosa population at low levels for up to 12 h post-infection. However, bacterial growth resumed afterward and reached levels similar to non-treated samples at 24 h post-infection. Host range analysis showed that 51.4% of the bacterial strains investigated were susceptible to phage BrSP1 and efficiency of plating (EOP) investigation indicated that EOP values in the strains tested varied from 0.02 to 1.72. Analysis of the phage genome revealed that it was a double-stranded DNA virus with 66,189 bp, highly similar to the genomes of members of the genus Pbunavirus, a group of viruses also known as PB1-like viruses.

Conclusion

The results of our “in vitro” bioassays and of our host range analysis suggested that Pseudomonas phage BrSP1 could be included in a phage cocktail to treat veterinary infections. Our EOP investigation confirmed that EOP values differ considerably among different bacterial strains. Comparisons of complete genome sequences indicated that phage BrSP1 is a novel species of the genus Pbunavirus. The complete genome of phage BrSP1 provides additional data that may help the broader understanding of pbunaviruses genome evolution.

Electronic supplementary material

The online version of this article (10.1186/s12866-019-1481-z) contains supplementary material, which is available to authorized users.

Protective efficacy of microencapsulated seaweed extracts for preventing Aeromonas infections in Oreochromis mossambicus

Sea weeds are valuable natural assets in aquaculture due to the presence of various bioactive active metabolites in them. Successful fish production and maintenance of disease free culturing systems in aquaculture with environment friendly practices is often affected by various environmental factors. Disease causing pathogens is one of the major factors. These can be controlled by the emerging technologies such as biopolymer based drug delivery systems, feed encapsulations processes and immersions of active ingredients which can possibly facilitate sustainable production by enhancing growth and immune responses in aquaculture animals. The focus of our study is on the identification of antibacterial and antioxidant compounds from two brown seaweeds, Gracilaria foliifera and Sargassum longifolium which have proven bioactive compounds. By a process of microencapsulation these bioactive compounds were encapsulated in the form of beads. Sodium caseinate and xanthan gum were mixed together to form the beads. This process helps to retain and protect the bio active ingredients from adverse reactions such as oxidation and nutritional deterioration. These microencapsulated beads were administered orally to 10 Oreochromis mossambicus the experimental fishes, with average body weight of 10-12 g and challenged against the pathogenic bacteria Aeromonas salmonicida to assess their antibacterial efficacy to control this bacterial pathogen. Microencapsulated bio active compounds were further characterized by FT-Raman, GC-MS, NMR, HPLC and SEM analysis. In this study, the effects of combined formulations of the different bioactive compounds were determined. Data obtained from the treatment of A. salmonicida infection in O. mossambicus using formulated bioactive compounds obtained from these seaweeds showed very high survival percentage in this species of fish.

Antibacterial efficacy of a fucoidan fraction (Fu-F2) extracted from Sargassum polycystum

In this study therapeutic potential of fucoidan fraction-2 (Fu-F2) isolated from Sargassum polycystum was evaluated for the development of antibacterial agent against the human and animal pathogenic bacteria by in vitro and in vivo analysis. The Fu-F2 contained 51.12 ± 0.86% of total sugar and 20.41 ± 0.91% of sulfate. The structural characterization of Fu-F2 was performed by HPLC, FTIR and NMR analysis and reported in our earlier study. The in vitro antibacterial assays such as MIC, MBC, killing kinetics, disk diffusion, protein leakage, ROS and confocal laser scanning microscopy demonstrate that Fu-F2 possesses the highest antibacterial activity against the tested pathogens. Among the tested pathogens, the highest antibacterial activity (21 ± 1.0 mm) was recorded at the concentration of 50 μg/ml against Pseudomonas aeruginosa and the lowest activity (16 ± 0.53 mm) was registered against Staphylococcus aureus. In the in vivo analysis, the pre-treatment group with Fu-F2 at the concentration of 15 mg/0.1 kg through feed exhibited the highest survival (83.4%) and antioxidant activities (p < 0.05) than the fish infected with pathogen. Thus, the present findings suggest that the Fu-F2 of S. polycystum encompasses significant antibacterial properties and that can be used as a therapeutic agent for controlling the bacterial disease.

Grape pomace flour alleviates Pseudomonas aeruginosa-induced hepatic oxidative stress in grass carp by improving antioxidant defense

Pseudomonas aeruginosa is a Gram-negative opportunistic bacterial pathogen in aquaculture systems being associated to extensive liver damage caused by oxidative stress in both marine and freshwater fish. Dietary supplementation with natural antioxidants is considered a rational strategy to prevent hepatic diseases involved with oxidative stress. Bio-residues resulting from the wine industry, such as grape pomace, are potential sources of bioactive phenolic compounds that can be applied as supplement for animal production. Thus, the aim of this study was to evaluate whether dietary supplementation with grape pomace flour (GPF) was able to prevent or reduce the hepatic oxidative damage of grass carp, Ctenopharyngodon idella, experimentally infected by P. aeruginosa. Hepatic reactive oxygen species (ROS), metabolites of nitric oxide (NOx), thiobarbituric acid reactive substances, and protein carbonylation levels were higher in fish experimentally infected by P. aeruginosa compared to the control group. Hepatic superoxide dismutase and catalase activities and antioxidant capacity against peroxyl radical levels were also higher in fish experimentally infected by P. aeruginosa compared to the control group. Dietary supplementation with 300 mg/kg GPF prevented all alterations elicited by P. aeruginosa, with the exception of protein carbonylation levels. The dietary supplementation with 150 mg/kg GPF was not able to avoid alteration of the analyzed variables, being results similar to those infected (positive control). Based on these results, dietary supplementation with 300 mg/kg GPF prevented P. aeruginosa-induced liver damage in grass carp, and this protective effect occurred through prevention on excessive ROS and NOx production, as well as via prevention of lipid damage. Moreover, 300 mg/kg GPF exerted its hepatoprotective effects by improving enzymatic and non-enzymatic antioxidant defense system. In summary, this supplementation can be an interesting approach to prevent P. aeruginosa-induced liver damage.

Effect of Dietary Supplementation of Novel Probiotic Bacteria Bacillus vireti 01 on Antioxidant Defence System of Freshwater Prawn Challenged with Pseudomonas aeruginosa

The aim of the present work was to isolate probiotic bacteria from the intestinal tract of healthy freshwater prawn Macrobrachium rosenbergii and to examine the effect of the isolated probiotic Bacillus vireti 01 in controlling Pseudomonas aeruginosa infection. This is probably the first report on the isolation of probiotic B. vireti 01 from the intestine of M. rosenbergii. The compounds present in B. vireti 01 were identified using GC-MS analysis. The effect of B. vireti 01-incorporated diet on survival and antioxidant enzymes was studied in M. rosenbergii for 2 weeks. Decreased mortality was observed in M. rosenbergii which were administered with the probiotic diet compared to control diet. The antioxidant defence enzymes activities such as SOD, catalase and GSH were analysed in various organs of M. rosenbergii probiotic-treated and control groups. Antioxidant enzyme activities were considerably lowered (p < 0.01) in the muscles, hepatopancreas and gills of prawns infected by P. aeruginosa when compared to that of prawns fed with the probiotic-supplemented diet. The histopathological results suggest that the hepatopancreas, gills and muscles infected with P. aeruginosa were altered structurally. The result of the present work demonstrates that the probiotic B. vireti 01 could be used as a substitute to antibiotics for treating P. aeruginosa infection in prawns.

Effects of glycinin and β-conglycinin on growth performance and intestinal health in juvenile Chinese mitten crabs (Eriocheir sinensis)

This study investigates the effects of two soybean antigens (glycinin and β-conglycinin) as an antinutritional substance in the diet on the growth, digestive ability, intestinal health and microbiota of juvenile Chinese mitten crabs (Eriocheir sinensis). The isonitrogenous and isolipidic diets contained two soybean antigens at two levels each (70 and 140 g/kg β-conglycinin, 80 and 160 g/kg glycinin) and a control diet without β-conglycinin or glycinin supplementation, and were used respectively to feed juvenile E. sinensis for seven weeks. Dietary inclusion of either glycinin or β-conglycinin significantly reduced crab survival and weight gain. The crabs fed diets containing soybean antigens had higher malondialdehyde concentrations and lower catalase activities in the intestine than those in the control. The activities of trypsin and amylase in the intestine were suppressed by dietary β-conglycinin and glycinin. Dietary glycinin or β-conglycinin impaired the immunity and morphological structure of intestine, especially the peritrophic membrane. The mRNA expression of constitutive and inducible immune responsive genes (lipopolysaccharide-induced TNF-α factor and interleukin-2 enhancer-binding factor 2) increased while the mRNA expression of the main genes related to the structural integrity peritrophic membrane (peritrophin-like gene and peritrophic 2) significantly decreased in the groups with soybean antigen addition. Soybean antigen could also change the intestinal microbial community. The abundance of pathogenic bacteria (Ochrobactrum, Burkholderia and Pseudomonas) increased significantly in both soybean antigen groups. Although pathogenic bacteria Vibrio were up-regulated in the glycinin group, the abundance of Dysgonomonas that degraded lignocellulose and ameliorated the gut environment decreased in the glycinin group. This study indicates that existence of soybean antigens (glycinin or β-conglycinin) could induce gut inflammation, reshape the community of gut microbiota, and cause digestive dysfunction, ultimately leading to impaired growth in crabs.

Antimicrobial activity of Terminalia catappa brown leaf extracts against Staphylococcus aureus ATCC 25923 and Pseudomonas aeruginosa ATCC 27853

The aim of this study was to determine the effects of various concentration of Terminalia catappa brown leaves extract which can inhibit the growth of Staphylococcus aureus ATCC 25923 and Pseudomonas aeruginosa ATCC 27853. The crushed-brown leaves of Terminalia catappa was extracted using 95% ethanol, filtered, and evaporated. The dried T. catappa extract was used to identify phytochemical content qualitatively. Total phenolic and flavonoid contents were also measured quantitatively from dried extract. The dried extracts were also dissolved in sterile aquadest and serial dilutions were prepared to final concentration of 30, 60 and 90%. A disc diffusion method was used to evaluate the antibacterial activity of various concentrations of ethanol extract of brown leaves of T. catappa. Inhibition zone diameter was measured to determine antibacterial activity. Gentamycin sulfate and distilled water were used as positive and negative controls, respectively. Dried ethanolic extract of brown T. catappa leaves contained flavonoid, quinon, phenolic, triterpenoid, and tannin. A total of 208.722 mg gallic acid equivalent/g extract of total phenolic and 35.7671 mg quercetin equivalent/g extract of total flavonoid were also found in the dried extract. The inhibition zone diameters of ethanolic extracts ranged from 1.73 to 9.06 mm ( S. aureus) and from 1.83 to 6.5 mm ( P. aeruginosa). The higher concentration of extract, the wider the inhibition zone diameters for both bacteria. P. aeruginosa was more resistant to high concentrations of extract (90%) than S. aureus. Ethanolic extracts of the brown leaves of T. catappa had different antibacterial effects against S. aureus and P. aeruginosa. The higher the concentration of extract, the wider the inhibition zone diameter for both bacteria. P. aeruginosa was more resistant to high concentrations of ethanolic extracts of the brown leaves of T. catappa.

Involvement of xanthine oxidase inhibition with the antioxidant property of nanoencapsulated Melaleuca alternifolia essential oil in fish experimentally infected with Pseudomonas aeruginosa

Nanoencapsulated Melaleuca alternifolia essential oil (tea tree oil, TTO) is a natural alternative treatment, with 100% therapeutic efficacy in fish experimentally infected with Pseudomonas aeruginosa, and has also potent protective effects linked with antioxidant properties. However, the pathways responsible for the antioxidant capacity remain unknown. Thus, this study evaluated whether the inhibition of seric xanthine oxidase (XO) activity can be considered a pathway involved in the antioxidant capacity of nanoencapsulated TTO in fish experimentally infected with P. aeruginosa. Seric samples from fish infected with P. aeruginosa showed increased XO activity, as well as increased uric acid and reactive oxygen species (ROS) levels. In contrast, the prophylactic treatment with nanoencapsulated TTO prevented these infection-induced alterations. Based on the evidence obtained, the upregulation of seric XO activity induced pro-oxidative effects in the serum of fish experimentally infected with P. aeruginosa, due to excessive formation of uric acid, which stimulates the release of ROS. This treatment was able to prevent the upregulated seric XO activity and, consequently, the excessive formation of uric acid and ROS. In summary, inhibition of seric XO activity can be considered a pathway involved in the antioxidant capacity of nanoencapsulated TTO in fish experimentally infected with P. aeruginosa.

Biosurfactant from a marine bacterium disrupts biofilms of pathogenic bacteria in a tropical aquaculture system

Bacterial infections are major constraints in aquaculture farming. These pathogens often adapt to the biofilm mode of growth and resist antibiotic treatments. We have used a non-toxic glycolipid biosurfactant (BS-SLSZ2) derived from a marine epizootic bacterium Staphylococcus lentus to treat aquaculture associated infections in an eco-friendly manner. We found that BS-SLSZ2 contained threose, a four-carbon sugar as the glycone component, and hexadecanoic and octadecanoic acids as the aglycone components. The critical micelle concentration of the purified glycolipid was 18 mg mL-1. This biosurfactant displayed anti-adhesive activity and inhibited biofilm formation by preventing initial attachment of cells onto surfaces. The biosurfactant (at a concentration of 20 μg) was able to inhibit Vibrio harveyi and Pseudomonas aeruginosa biofilms by 80.33 ± 2.16 and 82 ± 2.03%, respectively. At this concentration, it was also able to disrupt mature biofilms of V. harveyi (78.7 ± 1.93%) and P. aeruginosa (81.7 ± 0.59%). The biosurfactant was non-toxic towards Artemia salina. In vivo challenge experiments showed that the glycolipid was effective in protecting A. salina nauplii against V. harveyi and P. aeruginosa infections. This study highlights the significance of marine natural products in providing alternative biofilm controlling agents and decreasing the usage of antibiotics in aquaculture settings.

Efficacy of cell free supernatant from Bacillus licheniformis in protecting Artemia salina against Vibrio alginolyticus and Pseudomonas gessardii

Bacterial diseases are widespread in aquaculture farms and causative agents often adapt to biofilm mode of growth. These biofilms are detrimental to aquaculture species as they resist antibiotics and other agents that are used to control them. Two bacterial pathogens isolated from infected prawn samples were identified as Vibrio alginolyticus and Pseudomonas gessardii on the basis of morphological features, biochemical characteristics, 16S r RNA gene sequencing and phylogenetic analysis. Their pathogenic nature was confirmed by performing in vivo challenge experiments using Artemia salina as a model system. Seven days post infection, the mortality observed with V. alginolyticus and P. gessardii was 97 ± 4.08% and 77.5 ± 5.24%, respectively. The isolates formed extensive biofilms on polystyrene and glass surfaces. These infections could be controlled in an effective manner by using the cell free supernatant (CFS) of a tropical marine epizoic strain of Bacillus licheniformis D1 that is earlier reported to contain an antimicrobial protein (BLDZ1). The CFS inhibited biofilms in an efficient manner (82.35 ± 1.69 and 82.52 ± 1.11% for V. alginolyticus and P. gessardii, respectively) on co-incubation. In addition, pre-formed biofilms of V. alginolyticus and P. gessardii were also removed (84.53 ± 1.26 and 67.08 ± 1.43%, respectively). Fluorescence and scanning electron microscopic studies confirmed the antibiofilm potential of this protein on glass surfaces. The antibiofilm nature was due to the anti-adhesion and antimicrobial properties exhibited by the CFS. Treatment of A. salina with CFS (6 h prior to infections) was effective in protecting larvae against infections by field isolates. This study highlights the significance of marine natural products in providing alternative biofilm controlling agents to tackle infections and decreasing the usage of antibiotics in aquaculture settings.

Blood-brain barrier breakdown and myeloperoxidase activity in silver catfish experimentally infected with Pseudomonas aeruginosa

Central nervous system (CNS) infections continue to be an important cause of morbidity and mortality, and microbial invasion of the blood-brain barrier (BBB) is considered a prerequisite for CNS infections, which contribute to behavioural abnormalities and disease pathogenesis. Based on this information, the aim of this study was to evaluate whether Pseudomonas aeruginosa causes disruption of the BBB, and to investigate the involvement of cerebral myeloperoxidase (MPO) activity in this process in experimentally infected silver catfish. The permeability of the BBB to Evans blue dye increased in the infected animals on days three and six post-infection (PI) compared to the control group. Moreover, cerebral MPO activity and reactive oxygen species (ROS) levels also increased in the infected animals on days three and six PI compared to the control group. Based on this evidence, we concluded that P. aaeruginosa causes a disruption of the BBB, which may contribute to disease pathogenesis in the CNS. Moreover, the increase in cerebral MPO activity and ROS levels may be considered a pathway involved in BBB breakdown, allowing the passage of bacteria to the CNS.

Assessment of the correlation among antibiotic resistance, adherence to abiotic and biotic surfaces, invasion and cytotoxicity of Pseudomonas aeruginosa isolated from diseased gilthead sea bream

Improper uses of antibiotics to treat fish disease pose an increase of multidrug resistance in Pseudomonas aeruginosa. In order to escape host antimicrobial agents and induce cytotoxicity, different virulence properties are needed by these bacteria such as, biofilm formation, adhesion and invasion ability. This study was conducted to isolate Pseudomonas aeruginosa from diseased cultured gilthead sea bream. Seventeen isolates of Pseudomonas aeruginosa were identified by PCR. All of the isolates tested were susceptible to Gentamicin and Ciprofloxacin. Highest level of resistance was observed against Erythromycin, Ampicillin and Tetracycline. Among the 17 isolates, 11 showed multi-drug resistance. The isolates were screened for biofilm formation in abiotic surfaces, adherence, invasion and cytotoxicity against Hep-2 cells. We found that some strains were able to adhere to abiotic and biotic surface and to enter inside Hep-2 cells. Using cytochalasin D inhibitor, we observed a significant decrease in invasion of epithelial cells. The 17 washed bacterial cells induce variable degree of cytotoxicity. However, no cytotoxic effects on Hep-2 cells were obtained among the totality of cell free filtrate of Pseudomonas strains. By studying the relationship between different virulence properties, a significant positive correlation was obtained between both biofilm formation and adherence, and between adherence and invasion to epithelial cells. Subsequently, we found that the mean values of adhesion and invasion in the MDR group were significantly higher than those observed in the non-MDR group. Likewise, a significant positive correlation was found among adhesive and invasive capacities of Pseudomonas strains and their antibiotic resistance phenotypes.

Inhibition of the mitochondrial respiratory chain in gills of Rhamdia quelen experimentally infected by Pseudomonas aeruginosa: Interplay with reactive oxygen species

It has long been recognized that there are several infectious diseases linked to the impairment of enzymatic complexes of the mitochondrial respiratory chain, with consequent production of reactive oxygen species (ROS), that contribute to disease pathogenesis. In this study, we determined whether the inhibition on mitochondrial respiratory chain might be considered a pathway involved in the production of ROS in gills of Rhamdia quelen experimentally infected by P. aeruginosa. The animals were divided into two groups with six fish each: uninfected (the negative control group) and infected (the positive control group). On day 7 post-infection (PI), animals were euthanized and the gills were collected to assess the activities of complexes I-III, II and IV of the respiratory chain, as well as ROS levels. The activities of complexes I-III, II and IV of the respiratory chain in gills decreased, while the ROS levels increased in infected compared to uninfected animals. Moreover, a significant negative correlation was found between enzymatic activity of the complexes I-III and IV related to ROS levels in P. aeruginosa infected animals, corroborating to our hypothesis that inhibition on complexes of respiratory chain leads to ROS formation. Also, microscopic severe gill damage and destruction of primary and secondary lamellae were observed in infected animals, with the presence of hyperplasia, leukocytic infiltration and telangiectasia. In summary, we have demonstrated, for the first time, that experimental infection by P. aeruginosa inhibits the activities of mitochondrial complexes of respiratory chain and, consequently, impairs the cellular energy homeostasis. Moreover, the inhibition on mitochondrial complexes I-III and IV are linked to the ROS production, contributing to disease pathogenesis.

Human-Driven Microbiological Contamination of Benthic and Hyporheic Sediments of an Intermittent Peri-Urban River Assessed from MST and 16S rRNA Genetic Structure Analyses

Rivers are often challenged by fecal contaminations. The barrier effect of sediments against fecal bacteria was investigated through the use of a microbial source tracking (MST) toolbox, and by Next Generation Sequencing (NGS) of V5-V6 16S rRNA gene (rrs) sequences. Non-metric multi-dimensional scaling analysis of V5-V6 16S rRNA gene sequences differentiated bacteriomes according to their compartment of origin i.e., surface water against benthic and hyporheic sediments. Classification of these reads showed the most prevalent operating taxonomic units (OTU) to be allocated to Flavobacterium and Aquabacterium. Relative numbers of Gaiella, Haliangium, and Thermoleophilum OTU matched the observed differentiation of bacteriomes according to river compartments. OTU patterns were found impacted by combined sewer overflows (CSO) through an observed increase in diversity from the sewer to the hyporheic sediments. These changes appeared driven by direct transfers of bacterial contaminants from wastewaters but also by organic inputs favoring previously undetectable bacterial groups among sediments. These NGS datasets appeared more sensitive at tracking community changes than MST markers. The human-specific MST marker HF183 was strictly detected among CSO-impacted surface waters and not river bed sediments. The ruminant-specific DNA marker was more broadly distributed but intense bovine pollution was required to detect transfers from surface water to benthic and hyporheic sediments. Some OTU showed distribution patterns in line with these MST datasets such as those allocated to the Aeromonas, Acinetobacter, and Pseudomonas. Fecal indicators (Escherichia coli and total thermotolerant coliforms) were detected all over the river course but their concentrations were not correlated with MST ones. Overall, MST and NGS datasets suggested a poor colonization of river sediments by bovine and sewer bacterial contaminants. No environmental outbreak of these bacterial contaminants was detected.