Isolation, identification and vaccine development of serotype III Streptococcus parauberis in turbot (Scophthalmus maximus) in China

Abstract

Streptococcus parauberis is an important disease in farming fish that could infect a series of fish causing streptococcosis, which leads to significant economic losses. In this research, we first characterized the streptococcosis caused by S. parauberis in farming fish in China. In 2019, bacteria were isolated from diseased turbot in 3 farms located in Penglai, Haiyang, and Laizhou city, Shandong Province, and identified as S. parauberis by 16S rRNA sequencing and Biolog GenIII. Capsule polysaccharide (cps) genes of isolates were obtained by whole genome sequencing and aligned with the cps cluster in GenBank. By cps genes analysis, the isolates were all classified as serotype III, which were different from the isolates that infect flounder (Paralichthys olivaceus) in Japan and South Korea, but the same with the isolates in Spain and the USA reported recently. Then the serotype III S. parauberis vaccines were developed for turbot. The specific antibody could be detected in the vaccinated fish, and the specific antibody from oil emulsified vaccine group fish was significantly higher than that of the water-based vaccine group from 14 days post vaccination. The relative percent of survival were 78.00% and 100% for water-based vaccine and Marcol 52 emulsified vaccine, respectively. To our knowledge, this is the first report of S. parauberis infection in farming fish in China, and would provide important information for disease control and prevention for streptococcosis in aquaculture.