engleski

Evaluation of autologous vaccine against Vibrio harveyi in European sea bass (Dicentrarchus labrax)

Adriatic marine aquaculture is facing to the similar health challenges as of sea bass farming in other Mediterranean countries. In last decade, among bacterial diseases the most prevalent are outbreaks caused by Vibrio harveyi causing seerious losses during the summer months. Unfortunatelly, there is no commercial vaccine against V. harveyi and to prevent the losses in aquaculture of sea bass, we produced and tested autologous vaccine against this bacteria. V. harveyi was isolated from eyes, anterior kidneys, hearts and spleens of diseased sea bass from farm on the Eastern Adriatic on marine agar (MA) and tryptic soy agar (TSA) supplemented with 1.5% sodium chloride, incubated during 48h at 25°C. Typical bacterial colonies were purified and affiliation confirmed by polymerase chain reaction (PCR) using toxR primers and also using 16S rRNA sequencing. Serotyping was performed, and isolate used for vaccine belongs to the serovar A, known to cause the severe clinical symptoms. The bacterin was prepared by growing V. harveyi in Tryptic Soy Broth (TSB) with 1.5% NaCl using a 2L fermenters for 48h at 24°C. The culture was inactivated with 0.4% formaldehyde during 48h. Safety tests of the vaccines and protocols were performed using 20 fish per test group (unvaccinated and vaccinated) prior the vaccination and no mortalities was recorded in period of 40 days. The vaccination was performed in laboratory conditions by immersion and intraperitonaeal injection (IP). Vaccinated fish were challenged 36 days after vaccination both by immersion and intraperitonaeal injection. Control groups were mock vaccinated with sterile saline applying both procedures. Challenged fish in unvaccinated and vaccinated groups showed typical pathological signs of V. harveyi infection - haemorrhages at the fin bases. Immersion vaccination against V. harveyi of juvenile sea bass showed satisfactory RPS=63, thirty-six days post-vaccination after IP challenge and survival percentage of 99% (SP=99) after a challenge by immersion. IP vaccination gave RPS=100 with same challenge dose for testing group immersion vaccination. Autologous vaccine against vibriosis caused by V. harveyi showed to be effective protection for juvenile sea bass. The results were supported by higher gene expression of interleukins in spleen, kidney and intestines.

European sea bass, Vibrio harveyi infection, autologous vaccine

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