Characteristics that promote bacterial colonization of the intestinal mucosal surface were examined in two strains of the common fish pathogen Aeromonas hydrophila, with different pathogenicity. The characteristics examined were chemotactic activity towards mucus, bacterial adherence to mucus and growth in mucus. Intestinal gut mucus of healthy common carp was used. The results indicate that chemotaxis is not necessary for a bacterium to become pathogenic, but it may be a necessary parameter for a bacterium to be an obligate pathogen. Adhesion also seems to be a factor influencing pathogenicity. The results suggest that higher adhesion to mucus and subsequent growth is associated with differences in pathogenicity.

Mucins are high molecular weight glycoproteins produced by goblet cells and secreted on mucosal surfaces. We investigated biochemical and histochemical properties of intestinal mucins of virus-and parasite-free common carp Cyprinus carpio in response to a single peroral application of endotoxin (lipopolysaccharide = LPS). Intracellular mucins were quantified histochemically by their carbohydrate content and characterized by specific, lectin-based methods. In addition, secreted epithelial (intracellular) and luminal (extracellular) mucins were isolated and separated by downward gel filtration. Carbohydrate and protein content were determined photometrically. Subsequently, terminal glycosylation was characterized by a lectin-binding assay. A peroral endotoxin application altered intestinal secretion and composition of intestinal mucin glycoproteins in common carp. A statistically significant decrease in mature luminal mucins was demonstrated, linked to a new biosynthesis of intracellular mucin glycoproteins. Simultaneous changes in the glycosylation pattern of isolated mucins were found. The intestinal mucosal system is purported to provide a removal mechanism for bacterial noxes by increasing secretion of mucins inducing a flushing-out effect, in combination with altered glycosylation patterns that change adhesion properties. Consequently, pseudofaeces of fish, which are a common sign of intestinal parasitical infections, may also be interpreted as an elimination mechanism for strong bacterial noxes. KEY WORDS: Carp · Mucus · Intestinum · Endotoxin · Lipopolysaccharide Resale or republication not permitted without written consent of the publisherDis Aquat Org 77: [17][18][19][20][21][22][23][24][25][26][27] 2007 in fish are considered to be similar to those of mammals. As in mammals, there is production of secretory vesicles with neutral, acidic or sulphated glycoproteins (Shephard 1994, Bosi et al. 2005. Histological and histochemical studies also indicate that fishes with parasitic infections (like infected mammals) exhibit goblet cell hyperplasia and hypertrophy, whereby as a chronic reaction their intracellular mucins shift towards acidic and sulphated glycoprotein types (George & Nadakal 1981, Dezfuli et al. 2002, Bosi et al. 2005.However, to our knowledge little information is available on the biochemical composition of piscine glycoproteins and their response to enteric bacterial infections. We mimicked bacterial infection by an oral application of endotoxin. Endotoxins are lipopolysaccharide (LPS)-protein complexes synthesized mainly by gram-negative bacteria. LPS is an integrated part of the bacterial membrane. Endotoxin has, at least in mammals, a local and systemic immune-inducing function in inflammation reactions (Raetz 1990, Raetz & Whitfield 2002. Toxic effects are mainly mediated by cell receptors (TLR-4) and leucocyte mediators; however, there are numerous key differences between fish and mammals. In many in vitro studies on cells of lower vertebrates, such as fish, extremely high co...

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