Inhibition of the attachment of Flavobacterium branchiophilum to the gills of rainbow trout, Oncorhynchus mykiss (Walbaum)

Abstract

Preliminary experiments are described which aimed to identify compounds that could inhibit the attachment of Flavobacterium branchiophilum strains LAB4a and ATCC 35035 to the gills of rainbow trout. Total inhibition was never achieved, regardless of the compound tested. Formalin‐killed or acetone‐killed F. branchiophilum cells retained at least some of their adherent nature, relative to untreated (live) cells. Adherence was reduced by 22–33% following immersion of fish in one litre of water containing 0.21 mg of a homologous crude fimbrial extract. When fish were immersed in water containing hyperimmune rainbow trout antiLAB4a serum, a dose‐dependent decrease in attachment (a reduction of 15% to 63%) of LAB4a to the gills was observed. Rainbow trout anti‐LAB4a serum also reduced the attachment of ATCC 35035 to the gills, but this reduction was not significant. Adherence of LAB4a was not inhibited following exposure of fish to group 1 carbohydrates (arabinose, mannose and xylose), group 2 carbohydrates (dextrose, galactose and lactose), group 3 carbohydrates (galactosamine, glucosamine and fucose) or group 4 carbohydrates (N‐acetyl‐D‐glucosamine, N‐acetyl‐D‐galactosamine, N‐acetyl‐neuraminic acid and the globoceramide glycolipid from human erythrocytes). In contrast, when rainbow trout erythrocytes were incubated with the bacteria prior to bath challenge, this resulted in an 87% and 53% reduction in gill‐associated LAB4a and ATCC 35035 antigen, respectively, following immersion of rainbow trout in this suspension.

Complete Genome Sequence of the Fish Pathogen Flavobacterium branchiophilum

“…Bacterial attachment is essential in the initiation of mucosal infection, and previous reports have stressed the adherence properties of F. branchiophilum. Formalin-killed or acetone-killed bacterial cells retained part of their adherent nature, and adherence was never totally inhibited whatever the compound tested (42). In accordance with these findings, the FL-15 genome encodes 20 predicted adhesin precursors that could be implicated in cell-cell and cell-surface interactions.…”

Flavobacterium branchiophilum and F. succinicans associated with bacterial gill disease in rainbow trout Oncorhynchus mykiss (Walbaum) in water recirculation aquaculture systems

“…), with this presumption supported by previous BGD research (e.g. Byrne et al 1995;Ostland et al 1997;Derksen, Ostland & Ferguson 1998) and various F. branchiophilumspecific diagnostic approaches that have been developed. The latter include ELISA , IFAT (Heo, Kasai & Wakabayashi 1990), and PCR (Toyama, Kita & Wakabayashi 1996).…”

“…; Ostland et al . ; Derksen, Ostland & Ferguson ) and various F. branchiophilum ‐specific diagnostic approaches that have been developed. The latter include ELISA (MacPhee et al .…”

Secretion Systems in Gram-Negative Bacterial Fish Pathogens

“…Bacterial pathogens rely on the synergistic action of different virulence determinants and on specialized secretion systems to cause disease in susceptible hosts ( Finlay and Falkow, 1997 ; Thanassi and Hultgren, 2000 ). Initiation of infection is often triggered by adherence of the pathogen to the skin or mucosal surface of the host tissue using attachment mechanisms such as non-fimbrial adhesins ( Ostland et al, 1997 ; Weber et al, 2010 ; Guardiola et al, 2019 ), pili or fimbriae ( Ho et al, 1990 ; Mattick, 2002 ; Gerlach and Hensel, 2007 ; Craig et al, 2019 ) which recognize specific receptors. A successful uptake of the pathogen into host cells is then mediated by specific invasion factors (e.g., invasins) which are either membrane anchored proteins of the pathogen or are secreted through specialized secretion systems.…”