Vibriosi da Vibrio harveyi: studi di eziopatogenesi e di efficacia vaccinale nel branzino (Dicentrarchus labrax)

Vibrio harveyi is an emerging bacterial pathogen for marine aquaculture globally. In the European sea bass V. harveyi has been isolated in episodes of mortality characterized by ataxia, cutaneous and enteric lesions. In the present study, a polyphasic identification protocol for V. harveyi was standardized based on biochemical, molecular and proteomic methods and was evaluated by comparing a collection of 81 V. harveyi field isolates (fish and bivalve species) with V. harveyi reference strains and other 22 species of the family Vibrionaceae. The phenotypic evaluation was based on macromethod and micromethod (API20E) tests and growth on TCBS and CHROMagar Vibrio. Molecular analysis employed the sequencing of the housekeeping pyrH gene, and the species-specific amplification of the toxR gene. The protein profile was determined by MALDI-TOF analyzing the ribosomal protein content. The antibiotic susceptibility profile was evaluated on 51 V. harveyi strains, isolated from clinical episodes or environmental samples, applying the Kirby-Bauer method and determination of the minimum inhibitory concentration (MIC). The pathogenicity of different V. harveyi isolates in sea bass was investigated by experimental infections (immersion and intraperitoneal IP injection) and the induced anatomo-histopathological lesions were evaluated. A vaccine protocol based on a polyvalent bacterin was also developed to be administered by immersion or by IP, enriched with extracellular extract and emulsified or not with adjuvant. Safety tests and vaccine efficacy were carried out by determining the relative survival rate (RPS) for the various protocols. An indirect ELISA method was developed to compare the immune response (serum IgM) of the specimens vaccinated with the different protocols, highlighting a significantly greater response in the specimens inoculated IP with adjuvant vaccine.