In vivo adherence of Flavobacterium psychrophilum to mucosal external surfaces of rainbow trout (Oncorhynchus mykiss) fry

Abstract

The adherence of Flavobacterium psychrophilum to surfaces of epithelial tissues has been inconclusively suggested as a mechanism, which enables the bacterium to invade the host. Hence, the present study aimed to examine the adherence of the cells of two colony phenotypes, smooth and rough, of F. psychrophilum to mucosal tissues of rainbow trout fry and to test the skin mucus as a nutrient for the growth of F. psychrophilum. Fish were immersed in water containing 10 CFU mL F. psychrophilum for each colony phenotype. Mucosal tissue samples from fins, gills, skin and eyes, and swab samples from spleen and kidney were taken and inoculated onto TYES agar plates. Colony phenotypes of F. psychrophilum were identified and number of colonies counted. The results showed that cells of both phenotypes initially (0 h) adhered to all mucosal surfaces, but only the rough cells were still present on tissues 1 h post-immersion. Both phenotypes showed a tissue tropism with the fin tissue being the most adhered. Furthermore, skin mucus promoted the growth of both colony phenotypes. We suggest that the growth of F. psychrophilum cells in skin mucus apparently facilitates the bacterial adherence to mucosal surfaces, and the subsequent invasion into the host.

Stress Tolerance-Related Genetic Traits of Fish Pathogen Flavobacterium psychrophilum in a Mature Biofilm

“…However, there are few studies on F. psychrophilum comparing free-living vs. biofilm lifestyles (e.g., De la Fuente et al, 2013 ), and research based on mutants with defects in motility (Álvarez et al, 2006 ; Pérez-Pascual et al, 2015 ) has reported an attenuation of virulence in spread-deficient mutants compared to wild-type strains (Pérez-Pascual et al, 2017 ). These findings suggest that F. psychrophilum biofilm cells could be less virulent than motile free-living cells; however, this suggestion overlooks the fact that F. psychrophilum infections rely on initial attachment to mucosal external surfaces of fish (Papadopoulou et al, 2017 ) for cell colonization and long-term persistence of adhered cells. We have previously reported that strong and weak biofilm producers (LM-02-Fp and NCMB1947 T strains in the present study, respectively) share a genetic potential for virulence that is transcriptionally enhanced with respect to free-living cells (Levipan and Avendaño-Herrera, 2017 ).…”

More Than Gliding: Involvement of GldD and GldG in the Virulence of Flavobacterium psychrophilum

“…Skin mucus acts as a first barrier and is an important part of the fish immune system, containing numerous antibacterial factors secreted by skin cells, such as immunoglobulins, agglutinins, lectins, lysins, and lysozymes; but skin mucus can also be an important microenvironment and portal of entry for pathogenic bacteria (Benhamed et al, 2014 ). F. psychrophilum is able to adhere to fish skin mucus (Högfors-Rönnholm et al, 2015 ) and to different mucosal tissues such as fins, gills, skin, and eyes (Nematollahi et al, 2003b ; Papadopoulou et al, 2017 ). Exoproteome analyses revealed that both mutant strains display an important decrease in the amount of several putative adhesins.…”

The role of rpoS in the regulation of Vibrio alginolyticus virulence and the response to diverse stresses

“…Adhesion of the pathogen to the host surface constitutes a critical step in infection initiation (Chen et al., ; Shoemaker, LaFrentz, Peatman, & Beck, ), and multiple pathogenic bacteria show strong adhesion abilities (Lin et al., ; Papadopoulou, Dalsgaard, Lindén, & Wiklund, ; Qin, Lin, Chen, Xu, & Yan, ). Bacterial adhesion is regulated by different genes (Guo et al., ; Huang, Qin, et al., ; Jiang et al., ; Xu, Huang, Su, & Yan, ).…”