Lipopolysaccharide O-Antigen Prevents Phagocytosis of Vibrio anguillarum by Rainbow Trout (Oncorhynchus mykiss) Skin Epithelial Cells

Abstract

Colonization of host tissues is a first step taken by many pathogens during the initial stages of infection. Despite the impact of bacterial disease on wild and farmed fish, only a few direct studies have characterized bacterial factors required for colonization of fish tissues. In this study, using live-cell and confocal microscopy, rainbow trout skin epithelial cells, the main structural component of the skin epidermis, were demonstrated to phagocytize bacteria. Mutant analyses showed that the fish pathogen Vibrio anguillarum required the lipopolysaccharide O-antigen to evade phagocytosis and that O-antigen transport required the putative wzm-wzt-wbhA operon, which encodes two ABC polysaccharide transporter proteins and a methyltransferase. Pretreatment of the epithelial cells with mannose prevented phagocytosis of V. anguillarum suggesting that a mannose receptor is involved in the uptake process. In addition, the O-antigen transport mutants could not colonize the skin but they did colonize the intestines of rainbow trout. The O-antigen polysaccharides were also shown to aid resistance to the antimicrobial factors, lysozyme and polymyxin B. In summary, rainbow trout skin epithelial cells play a role in the fish innate immunity by clearing bacteria from the skin epidermis. In defense, V. anguillarum utilizes O-antigen polysaccharides to evade phagocytosis by the epithelial cells allowing it to colonize rapidly fish skin tissues.

Does Virulence Assessment of Vibrio anguillarum Using Sea Bass (Dicentrarchus labrax) Larvae Correspond with Genotypic and Phenotypic Characterization?

“…Over the last couple of years, knowledge of the virulence of this bacterium has been largely increased by the use of molecular and biochemical analysis approaches [9], [10]. In general, virulence factors in V. anguillarum have been classified into those that are necessary for chemotaxis and motility, for adhesion and invasion, including proteases [11], [12], hemolysins [13]–[16], lipopolysaccharides (LPS) [17]–[19], and those that are required for bacterial proliferation and persistence. Regarding the latter, it is for example known that siderophore-mediated iron-sequestering systems, enabling growth in iron-limiting conditions, contribute significantly to the virulence of this pathogen.…”

The mucosal immune system of fish: The evolution of tolerating commensals while fighting pathogens

“…Similarly, a gut epithelial cell line from rainbow trout, RTgutGC, was recently developed [62] and epithelial cell lines from other origins (non-intestinal) are available from a number of teleost species. Primary skin epithelial cell cultures from rainbow trout were instrumental to reveal the ability of this bacterial pathogen to evade endocytosis by epithelial cells [63]. Since the skin (and gills) of aquatic vertebrates lacks keratinization, they secrete mucus, and they are formed by living cells (Figure 1), the epithelial cells of these tissues are likely to carry important immune functions as it is the case in the gut.…”

Vibriophages Differentially Influence Biofilm Formation by Vibrio anguillarum Strains

“…The persistence of Vibrio pathogens in aquaculture has been attributed to their ability to form biofilms with increased tolerance of disinfectants and antibiotics (4,5). Moreover, the first stage of infection involves biofilm-like microcolonies in the skin tissue, causing chronic infection (5).…”