Characterization of the virulence of Harveyi clade vibrios isolated from a shrimp hatchery in vitro and in vivo, in a brine shrimp (Artemia franciscana) model system

Vibrios belonging to the Harveyi clade are important pathogens of a large number of marine animals in the aquaculture industry. In this study, six isolates (H1 to H6) were obtained from a shrimp hatchery in Rio Grande do Norte (Natal-Area, Brazil), which had been confronted with disease outbreaks in 2009. The aim was to characterize the virulence of these isolates, both in vitro (virulence factor production) and in vivo (virulence towards gnotobiotic brine shrimp, Artemia franciscana, larvae) and to compare these characteristics to those of the most virulent pathogen in the brine shrimp model described to date, Vibrio campbellii LMG 21363. Of all 6 isolates, H5 and H6 were found to be the most virulent ones and were therefore selected for further characterization. Isolate H5 exhibited a similar virulence as the control strain, while H6 exhibited a higher virulence, both in gnotobiotic and conventionally reared brine shrimp. Both H5 and H6 were motile and produced all of the lytic enzymes tested (hemolysin, caseinase, gelatinase, lipase and phospholipase). Although H6 was the most virulent isolate in vivo, this was not reflected in the highest production of all virulence factors tested. Finally, isolates H5 and H6 were identified to belong to the Harveyi clade of vibrios.