Treatment of vibriosis in European sea bass larvae, Dicentrarchus labrax L., with oxolinic acid administered by bath or through medicated nauplii of Artemia franciscana (Kellogg): efficacy and residual kinetics

Development of phage delivery by bioencapsulation of artemia nauplii with Edwardsiella tarda phage (ETP-1)

This study proposed that phage-enriched artemia could be a useful tool for transferring phage into the cultured fish (larvae or adult) as a feed, and introduce mode of phage administration and its safety in concern of tissue adaptation for efficient phage therapy in aquatic animals. First, whether Edwardsiella tarda phage (ETP-1) could attach or ingest by the artemia and optimum time period for the ETP-1 enrichment with artemia were investigated. ETP-1 dispersion, abundance and persistency, and zebrafish immune transcriptional responses and histopathology were evaluated after feeding the fish with ETP-1-enriched artemia. Hatched artemia nauplii (36 h) were enriched with 1.90 × 10¹¹ PFUmL^-1 of ETP-1, and maintained at 25 °C. The highest enrichment level was obtained after 4 h (3.00 × 10⁹ PFUmL^-1), and artemia were alive and active similar to control for 8 h. ETP-1 disseminated dose dependently to all the tissues rapidly (12 h). However, when feeding discontinued, it drastically decreased at day 3 with high abundance and persistency in the spleen (1.02 × 10³) followed by the kidney (4.00 × 10¹) and the gut (1 × 10¹ PFUmL^-1) for highest ETP-1-enriched artemia dose. In contrast, during continuous delivery of ETP-1-enriched artemia, ETP-1 detected in all the tissues (at day 10: gut; 1.90 × 10⁷, kidney; 3.33 × 10⁶, spleen; 5.52 × 10⁵, liver; 6.20 × 10⁴ PFUmL^-1mg^-1 tissues). Though the phage abundance varied, results indicated that oral fed ETP-1-enriched artemia disperse to the neighboring organs, even the absence of host as phage carrier. Non-significant differences of immune transcriptional and histopathology analysis between ETP-1-enriched artemia fed and controls suggest that no adverse apparent immune stimulation in host occurred, and use of ETP-1 at 10¹¹ PFUmL^-1 was safe. With further supportive studies, live artemia-mediated phage delivery method could be used as a promising tool during phage therapy against pathogenic bacteria to control aquatic diseases.

Recombinant DnaK Orally Administered Protects Axenic European Sea Bass Against Vibriosis

Vibrio anguillarum causes high mortality in European sea bass (Dicentrarchus labrax) larviculture and is a hindering factor for successful sustainable aquaculture of this commercially valuable species. Priming of the innate immune system through administration of immunostimulants has become an important approach to control disease outbreaks in marine fish larviculture. This study was conducted to evaluate immunostimulation by Escherichia coli HSP70 (DnaK) in axenic European sea bass larvae in order to protect the larvae against vibriosis. DnaK stimulates the immune response in crustaceans and juvenile fish against bacterial infections. The use of axenic fish larvae allows to study immunostimulation in the absence of an interfering microbial community. At 7 days post-hatching, larvae received a single dose of alginate encapsulated recombinant DnaK. Two non-treated control groups in which animals either received empty alginate microparticles (C1) or no alginante microparticles (C2 and C3) were included in the study. Eighteen hours later, all larvae, except the ones from group C3 (non-infected control) were challenged with V. anguillarum (10⁵ CFU, bath infection). Mortality was daily recorded until 120 h post infection and at 18, 24, and 36 h post infection, larvae were sampled for expression of immune related genes. Results showed that V. anguillarum induced an immune response in axenic sea bass larvae but that the innate immune response was incapable to protect the larvae against deadly septicaemic disease. In addition, we showed that administration of alginate encapsulated DnaK to axenic European sea bass larvae at DAH7 resulted in a significant, DnaK dose dependent, upreglation of immune sensor, regulatory and effector genes. Significant upregulation of cxcr4, cas1 and especially of hep and dic was correlated with significant higher survival rates in V. anguillarum infected larvae. In the future recombinant DnaK might perhaps be used as a novel immunostimulant in sea bass larviculture.

Modulation of Innate Immune-Related Genes and Glucocorticoid Synthesis in Gnotobiotic Full-Sibling European Sea Bass (Dicentrarchus labrax) Larvae Challenged With Vibrio anguillarum

Although several efforts have been made to describe the immunoendocrine interaction in fish, there are no studies to date focusing on the characterization of the immune response and glucocorticoid synthesis using the host-pathogen interaction on larval stage as an early developmental stage model of study. Therefore, the aim of this study was to evaluate the glucocorticoid synthesis and the modulation of stress- and innate immune-related genes in European sea bass (Dicentrarchus labrax) larvae challenged with Vibrio anguillarum. For this purpose, we challenged by bath full-sibling gnotobiotic sea bass larvae with 10⁷ CFU mL^-1 of V. anguillarum strain HI 610 on day 5 post-hatching (dph). The mortality was monitored up to the end of the experiment [120 hours post-challenge (hpc)]. While no variations were registered in non-challenged larvae maintained under gnotobiotic conditions (93.20% survival at 120 hpc), in the challenged group a constant and sustained mortality was observed from 36 hpc onward, dropping to 18.31% survival at 120 hpc. Glucocorticoid quantification and expression analysis of stress- and innate immunity-related genes were carried out in single larvae. The increase of cortisol, cortisone and 20β-dihydrocortisone was observed at 120 hpc, although did not influence upon the modulation of stress-related genes (glucocorticoid receptor 1 [gr1], gr2, and heat shock protein 70 [hsp70]). On the other hand, the expression of lysozyme, transferrin, and il-10 differentially increased at 120 hpc together with a marked upregulation of the pro-inflammatory cytokines (il-1β and il-8) and hepcidin, suggesting a late activation of defense mechanisms against V. anguillarum. Importantly, this response coincided with the lowest survival observed in challenged groups. Therefore, the increase in markers associated with glucocorticoid synthesis together with the upregulation of genes associated with the anti-inflammatory response suggests that in larvae infected with V. anguillarum a pro-inflammatory response at systemic level takes place, which then leads to the participation of other physiological mechanisms at systemic level to counteract the effect and the consequences of such response. However, this late systemic response could be related to the previous high mortality observed in sea bass larvae challenged with V. anguillarum.

Experimental infection model for vibriosis in Dover sole (Solea solea) larvae as an aid in studying its pathogenesis and alternative treatments

Severe economic losses due to diseases in marine larviculture may be linked to vibriosis. To better understand the pathogenesis of vibriosis and evaluate new ways to prevent and combat this important disease, there is a great need for reliable and reproducible experimental infection models. The present study aimed at developing a challenge model for vibriosis in Dover sole larvae and testing its applicability to study the effect of the probiotic treatment. For that purpose, larvae were challenged at 10 days post hatching with Vibrio anguillarum WT, V. anguillarum HI610 or V. harveyi WT. Following administration of V. anguillarum WT via immersion at 1 × 10⁷ colony forming units/mL, a larval mortality of 50% was observed at 17 days post-inoculation. In a next step, the probiotic potential of 371 isolates retrieved from Dover sole was assessed by screening for their inhibitory effects against Vibrio spp. and absence of haemolytic activity. One remaining isolate (V. proteolyticus) and V. lentus, known for its protective characteristics in seabass larvae, were further tested in vivo by means of the pinpointed experimental infection model. Neither isolate provided via the water or feed proved to be protective for the Dover sole larvae against challenge with V. anguillarum WT. This developed challenge model constitutes a firm basis to expedite basic and applied research regarding the pathogenesis and treatment of vibriosis as well as for studying the impact of (a)biotic components on larval health.

Validation of a Chiral Liquid Chromatographic Method for the Degradation Behavior of Flumequine Enantiomers in Mariculture Pond Water

In this work, flumequine (FLU) enantiomers were separated using a Chiralpak OD-H column, with n-hexane-ethanol (20:80, v/v) as the mobile phase at a flow rate of 0.6 mL/min. Solid phase extraction (SPE) was used for cleanup and enrichment. The limit of detection, limit of quantitation, linearity, precision, and intra/interday variation of the chiral high-performance liquid chromatography (HPLC) method were determined. The developed method was then applied to investigate the degradation behavior of FLU enantiomers in mariculture pond water samples. The results showed that the degradation of FLU enantiomers under natural, sterile, or dark conditions was not enantioselective. Chirality 28:649-655, 2016. © 2016 Wiley Periodicals, Inc.