Isolation and Genetic Characterization of Streptococcus iniae Virulence Factors in Adriatic Sturgeon (Acipenser naccarii)

The first case of infection of Streptococcus iniae in Adriatic sturgeon (Acipenser naccarii) was
recently reported in a raceway system located in Northern Italy. A second episode of infection in
sturgeons with absence of mortality and evident clinical signs, was registered in November 2020 in
the same farm and is reported in this study. Histopathological changes observed in infected organs
are described. The strains isolated in the two episodes were compared using molecular analysis based
on PCR, phylogeny and virulence factors analysis. Not all the major virulence factors were detected
for the two strains; in particular the strains 78697, isolated in November, lacks cpsD, compared to
the strains 64844, isolated in September. Moreover, genetic variations were reported for lctO and
pmg genes. These findings let us hypothesize a different virulence of the strains in accordance with
clinical findings related to the sturgeons.