Germ-free sea bass Dicentrarchus labrax larval model: a valuable tool in the study of host-microbe interactions

Abstract

A thorough understanding of host−microbe interactions is crucial for more efficient disease management in the marine larviculture industry. As demonstrated in terrestrial animal research, gnotobiotic systems (involving animals cultured in germ-free conditions or inoculated with known microorganisms) are excellent tools to extend our understanding of the mechanisms involved in host−microbe interactions and allow the evaluation of new treatments for diseases. In this study, we introduce a germ-free European sea bass Dicentrarchus labrax larval model, independent of the continuous addition of antimicrobial agents. This model has an experimental set-up that allows addition of live feed to the larvae without compromising the germ-free status. This model will facilitate and render aquaculture research more effective in terms of mitigation fish larval diseases.KEY WORDS: Aquaculture · Gnotobiotic · Pathogen · Larvae Resale or republication not permitted without written consent of the publisherDis Aquat Org 117: [177][178][179][180][181][182][183][184][185] 2016 towards more strict regulations on the use of antibiotics in the aquaculture sector (Suba singhe et al. 2001, Romero et al. 2012, hence calling for alternative, sustainable methods to which the aquaculturist can resort for preventing and controlling disease outbreaks. Several environmentally friendly prophylactic disease treatments have been the focus of recent research, i.e. probiotics, prebiotics, vaccines, immunostimulants or antimicrobial peptides (Merrifield & Ringø 2014).A judicious and scientifically supported application of the abovementioned alternatives warrants a thorough testing of their efficacy and safety under standardized and controlled experimental conditions (Smith et al. 2003). However, the stochastic colonization of larvae by microorganisms may hinder the establishment of a reproducible experimental set-up by generating high inter-individual and inter-batch variability in the composition of the standing microbial community. Hence, from a microbiological point of view, iterating experimental conditions using conventional animals is almost impossible (Fjellheim et al. 2012). The development of test systems in which the researcher has complete control over the microbial community structure, by adopting a germ-free or gnotobiotic model, was revolutionary in this respect. As already demonstrated in multiple terrestrial animal studies, gnotobiotic models are an excellent tool to extend our understanding of (1) the nutritional requirements of host organisms, (2) host−microbe interactions and (3) host metabolic functions (Gordon & Pesti 1971, Wostmann 1996, Marques et al. 2005. Despite the significant increase in the use of fish as experimental animals during the last decades (Marques et al. 2005, Schaeck et al. 2013) and the stressed importance of raising aquatic organisms gnotobiotically (Bates et al. 2006), the current know-how of rearing gnotobiotic aquatic organisms is much more limited compared to the more traditional mammalian l...

Under Pressure: Interactions between Commensal Microbiota and the Teleost Immune System

“…While it is possible, though labor intensive, to maintain a zebrafish under germ-free conditions past this early life stage, no studies have been published using adult germ-free zebrafish. Conversely, a germ-free seabass model that incorporates germ-free feeding of live prey has recently been developed allowing for larvae to survive for at least 16 days post hatching, if not longer (9). Future refinement of the germ-free rearing technique in zebrafish and other teleost species, as well as identification of cell markers, production of reagents, and production of transgenic lines with reporters for or knockouts of important immune genes, will allow for a deeper understanding of the types of systemic immune responses that microbes are capable of inducing during development and adulthood in teleosts.…”

“…Zebrafish are a small, genetically manipulable, and provide the advantage of being transparent during the larval life stage, which makes them a useful model for studying immune system dynamics in response to microbial colonization. Only recently, germ-free seabass ( Dicentrarchus labrax ) have been produced, allowing the study of the interactions between microbiota and a fish host in the seawater environment (9). Future work focused on the identification of candidate microbial species, which can be introduced via probiotics or eliminated using antibiotics will be essential to produce treatment plans applicable to improving fish health in aquaculture conditions.…”

Phenotypic effects of antibiotic-induced axenity and egg disinfection in early larval European seabass (Dicentrarchus labraxL.)

“…Numerous reasons might explain not reporting the same beneficial result on hatchability in the current study. In general, the use of disinfectants such as glutaraldehyde has been shown to have varying results on hatching percentages, growth rates and the survival of fish larvae, depending on their type, concentration, duration of exposure, stage of egg development on which they are being applied, and the species (Ben‐Atia et al., ; Douillet & Holt, ; Escaffre, Bazin & Bergot, ; Schaeck et al., ). The initial bacterial load could have been higher in the present experiment, with the disinfection not reducing it to a point where a difference in hatching percentages would be demonstrated.…”

“…() and Schaeck et al. () found a reduced total length growth of xenic European seabass larvae versus germ free on DAH 6, 9, 12 and 15. However, beyond these differences in total length, detailed knowledge of the phenotypic effects of antibiotic‐induced axenic conditions on the larvae is absent.…”

“…The effect of disinfectants on the eggs and the hatched larvae is quite variable, as it depends on many factors, such as the species on which they are applied, the specific developmental stage, the physiological state of the broodstock, the concentration and exposure time (De Swaef, Van den Broeck, Dierckens, & Decostere, and references therein). However, they can be considered an extra stress factor detrimental to eggs that come from a suboptimal batch quality (Schaeck et al., ), and they have been known to produce adverse effects, such as reduced stress tolerance and larvae malformations (De Swaef et al., ).…”