Evidence for the facultative intracellular behaviour of the fish pathogen Vibrio ordalii

Abstract

Vibrio ordalii is an extracellular, Gram‐negative bacterium that produces vibriosis in salmonids. While pathogenesis is not fully understood, this bacterium has numerous likely genes for adhesion, colonization, invasion factors and, as recently suggested, intracellular behaviour. Therefore, this study aimed to clarify possible intracellular behaviour for V. ordalii Vo‐LM‐18 and ATCC 33509T in the fish‐cell lines SHK‐1 and CHSE‐214. Confocal microscopy revealed Vo‐LM‐18 and ATCC 33509T inside cytoplasm in both fish‐cell lines at 4 hr post‐inoculation (hpi). At 8 and 16 hpi, the proportion of fish cells invaded by both strains increased. Moreover, intracellular V. ordalii were observed after 8 hpi inside mouse embryonic fibroblasts (MEF), demonstrating that entry was not due to a cellular phagocytosis process. Flow cytometry confirmed immunocytochemistry results, with both V. ordalii evidencing statistically significant differences in the number of infected cells between 8 and 16 hpi. Interestingly, V. ordalii infection did not significantly damage fish cells, as determined by LDH liberation. Viable counts at 8 hpi detected, on average for both lines, 176 ± 47 CFU/ml of culturable intracellular Vo‐LM‐18 and ATCC 33509T cells. These in vitro findings support the facultative intracellular behaviour of V. ordalii and may be of importance for understanding pathogenicity and survival in aquatic environments.

Identification and characterization of outer membrane vesicles from the fish pathogen Vibrio ordalii

“…For example, some strains of V. ordalii and V. anguillarum fall within the same serological group (serotype O2) (Mutharia, Raymond, Dekievit, & Stevenson, 1993; Silva‐Rubio, Avendaño‐Herrera, Jaureguiberry, Toranzo, & Magariños, 2008), and both exhibit facultative intracellular behaviour. This intracellular behaviour was previously reported in V. ordalii through the use of flow cytometry, with results concluding that this bacterium can survive for 8 hours in the CHSE‐214 cell line without causing damage, suggesting pathogenicity mechanisms not yet elucidated for the Vibrio genus (Avendaño‐Herrera et al, 2019; Hong et al, 2009). Genes likely associated with adhesion, colonization and invasion factors; exotoxin production; cell surface components; and iron uptake systems have also been identified in V. ordalii (Naka, López, & Crosa, 2008; Ruiz et al, 2016).…”

Emerging Research Topics in the Vibrionaceae and the Squid–Vibrio Symbiosis

“…Vibrio anguillarum , another fish pathogen, can also survive in salmon phagocytes [ 91 ]. Vibrio ordalii can live inside fish cells too [ 92 ]. Vibrio shiloi and Vibrio coralliilyticus can grow inside the cells of coral tissue [ 93 , 94 ].…”