title: Comparative analysis of innate immune responses to Streptococcus phocae strains in Atlantic salmon (Salmo salar) and rainbow trout (Oncorhynchus mykiss).
abstract: Streptococcus phocae subsp. salmonis is a Gram-positive bacterium that causes mortality only in Atlantic salmon (Salmo salar) farmed in Chile, even when this species is co-cultured with rainbow trout (Oncorhynchus mykiss). This susceptibility could be determined by innate immune response components and their responses to bacterial infection. This fish pathogen shares subspecies status with Streptococcus phocae subsp. phocae isolated from seals. The present study compared innate immune system mechanisms in Atlantic salmon and rainbow trout when challenged with different S. phocae, including two isolates from Atlantic salmon (LM-08-Sp and LM-13-Sp) and two from seal (ATCC 51973(T) and P23). Streptococcus phocae growth was evaluated in the mucus and serum of both species, with rainbow trout samples evidencing inhibitory effects. Lysozyme activity supported this observation, with significantly higher (p < 0.01) expression in rainbow trout serum and mucus as compared to Atlantic salmon. No differences were found in phagocytic capacity between fish species when stimulated with ATCC 51973(T) and P23. Against all S. phocae strains, rainbow trout and Atlantic salmon showed up to two-fold increased bactericidal activity, and rainbow trout demonstrated up to three-fold greater reactive oxygen species production in macrophages. In conclusion, the non-specific humoral and cellular barriers of Atlantic salmon were immunologically insufficient against S. phocae subsp. salmonis, thereby facilitating streptococcosis. Moreover, the more robust response of rainbow trout to S. phocae could not be attributed to any specific component of the innate immune system, but was rather the consequence of a combined response by the evaluated components.
authors.affiliation: Laboratorio de Patología de Organismos Acuáticos y Biotecnología Acuícola, Departamento de Ciencias Biológicas, Facultad de Ciencias Biológicas, Universidad Andrés Bello, Viña del Mar, Chile; Interdisciplinary Center for Aquaculture Research (INCAR), Concepción, Chile.
authors.forename: Soraya
authors.initials: S
authors.lastname: Salazar
authors.affiliation: Interdisciplinary Center for Aquaculture Research (INCAR), Concepción, Chile; Instituto de Bioquímica y Microbiología, Facultad de Ciencias, Universidad Austral de Chile, Valdivia, Chile.
authors.forename: Cristian
authors.initials: C
authors.lastname: Oliver
authors.affiliation: Interdisciplinary Center for Aquaculture Research (INCAR), Concepción, Chile; Instituto de Bioquímica y Microbiología, Facultad de Ciencias, Universidad Austral de Chile, Valdivia, Chile.
authors.forename: Alejandro J
authors.initials: AJ
authors.lastname: Yáñez
authors.affiliation: Laboratorio de Patología de Organismos Acuáticos y Biotecnología Acuícola, Departamento de Ciencias Biológicas, Facultad de Ciencias Biológicas, Universidad Andrés Bello, Viña del Mar, Chile; Interdisciplinary Center for Aquaculture Research (INCAR), Concepción, Chile; Centro de Investigación Marina Quintay (CIMARQ), Quintay, Chile. Electronic address: reavendano@yahoo.com.
authors.forename: Ruben
authors.initials: R
authors.lastname: Avendaño-Herrera
mesh_terms: D000818:Animals; D002677:Chile; D004198:Disease Susceptibility / Q000276:immunology / Q000662:veterinary; D005393:Fish Diseases / Q000276:immunology*; D007113:Immunity, Innate; D008264:Macrophages / Q000276:immunology; D009093:Mucus / Q000276:immunology; D017686:Oncorhynchus mykiss; D020317:Salmo salar; D013290:Streptococcal Infections / Q000276:immunology / Q000662:veterinary*; D013291:Streptococcus / Q000502:physiology*
keywords: Atlantic salmon; Immune response; Rainbow trout; Streptococcus phocae