An aerolysin‐like enterotoxin from Vibrio splendidus may be involved in intestinal tract damage and mortalities in turbot, Scophthalmus maximus (L.), and cod, Gadus morhua L., larvae

Abstract

Vibrio splendidus is a pathogen that can cause major losses during the early stages of larval turbot rearing when live feed (rotifers or Artemia) is used. As haemolytic bacteria have often been associated with larval rearing losses, we studied the role of the V. splendidus haemolysin in infection of larvae. From a bank of over 10,000 transposon mutants of V. splendidus, two different types of haemolysin-negative mutants were obtained. Both had lost virulence for larval fish, and immunohistochemistry showed that the transposon mutant studied colonized the turbot larval intestinal tract at a similar level to the wild-type organism but did not cause damage or signs of enteritis found with the wild-type organism. One transposon insertion site was located within a gene with high homology to aerolysin, the cytolytic toxin produced by several Aeromonas spp. The haemolysin, which we have termed vibrioaerolysin, had properties similar to aerolysin and osmotic protection studies showed that it formed pores in the membranes of erythrocytes of similar diameter to those of aerolysin. The Tn10 insertion site of the second transposon mutant was in an adjacent ToxR-like gene, suggesting that this might control expression of the vibrioaerolysin. The gastroenteritis caused by Aeromonas spp. in humans is considered to be due to production of aerolysin causing cyclic AMP-dependent chloride secretion in cells of the gastrointestinal tract. Damage to the intestinal tract of marine fish larvae could occur in a similar way, and it is possible that several Vibrio spp. found in the developing bacterial flora of the larval fish gut can secrete aerolysin-like toxins leading to death of larvae in the early rearing stages. Routine bacteriological screening on blood agar plates of live feed is recommended with measures to reduce the concentrations of haemolytic bacteria in rearing systems.

In vitro and in vivo evaluation of lactic acid bacteria of aquatic origin as probiotics for turbot (Scophthalmus maximus L.) farming

“…Moreover, two LAB strains selected based on their antimicrobial activity against turbot pathogens and probiotic properties were evaluated in vivo for their use as probiotics in turbot farming. Most of the tested LAB displayed antimicrobial activity, likely due to the production of organic acids, against T. maritimum and V. splendidus, two pathogens associated with high economical losses in turbot farming [2,3]. Lc.…”

“…In this work, we also investigated the ability of the eight LAB to inhibit the adhesion of the turbot pathogens T. maritimum NCIMB2154 and V. splendidus CECT528 to mucus. Skin mucus was used for the studies of the adhesion inhibition of T. maritimum NCIMB2154, since tenacibaculosis is commonly associated with lesions on the fish body surface [44]; however, the assays with V. splendidus CECT528 were carried out using intestinal mucus because this species causes damage in the intestinal tract [3]. Adhesion of both pathogens to turbot mucus was significantly reduced by all LAB (12.0e56.3%), except E. faecium CV1 that was only effective to reduce adhesion (44.1%) of V. splendidus CECT528 to intestinal mucus.…”

“…Tenacibaculosis (or flexibacteriosis) is a bacterial disease caused by Tenacibaculum maritimum (formerly, Flexibacter maritimus), a Gram-negative filamentous biofilm-forming microorganism that affects cultured adults and juvenile marine fish, with the latter suffering the most severe form of the disease [2]. Vibriosis is one of the main bacterial diseases that causes most of the economical problems in fish marine culture, and it is provoked by several species of fish-pathogenic vibrios [2,3]. One of the most relevant pathogenic vibrio species is Vibrio splendidus, a Gram-negative microorganism linked with high rates of mortality in larval turbot rearing fed with live feed [3].…”

“…Vibriosis is one of the main bacterial diseases that causes most of the economical problems in fish marine culture, and it is provoked by several species of fish-pathogenic vibrios [2,3]. One of the most relevant pathogenic vibrio species is Vibrio splendidus, a Gram-negative microorganism linked with high rates of mortality in larval turbot rearing fed with live feed [3]. In the fish farming sector, antibiotics have been used for therapeutic purposes and as prophylactic agents, leading to the development of antibiotic resistances and, consequently, to public health concerns in human and animal medicine worldwide [4].…”

Aeromonas hydrophila induces intestinal inflammation in grass carp (Ctenopharyngodon idella): An experimental model

“…Under intensive culture conditions, enteritis (or intestinal inflammation) is emerging as a major cause of high mortality in farmed fish, causing huge annual economic losses (Lee et al, 2002;Soffientino et al, 1999). Bacterial enteritis is probably the most common intestinal disease suffered by freshwater fish (Lü et al, 2011;Macpherson et al, 2012;Muroga et al, 1990;Xu et al, 1987Xu et al, , 1988. Among the bacterial pathogens identified thus far, Aeromonas hydrophila is generally considered a major pathogen in almost all animal taxa, and causes intestinal inflammation in fish (Cascón et al, 2000;Xu et al, 1988).…”