Abstract:
Luminescent Vibriosis caused by Vibrio harveyi and Vibrio campbelliiis a devastating disease in aquatic spp including
finfish and shell fish. These vibrios are luminous Gram-negative bacteria widely distributed in the marine
environment. Luminescence is an outcome of quorum sensing (bacterial cell to cell communication). Since luminous
vibrios are serious pathogens causing severe losses in aquaculture, gnotobioticArtemia (Brine shrimp) was used as
the host animal (in vivo model) to examine the virulence of luminous vibrios in a challenged experiment. In this study
wild-type V. harveyi BB120, V. campbellii LMG 21363, quorum sensing mutants of V. harveyi BB120 and their
previously reported non-luminescent isogenic counterparts were used. In addition quorum sensing maximally active
mutant JAF483 (QS+) which is a constitutively luminescence and quorum sensing inactive mutant JAF548 (QS-)
which is a dark (non-luminescent) mutant were also used. This study investigated the expression levels of the some
virulence gene regulator (luxR) and virulence factors (metalloprotease vhp and hemolysin vhh) by reverse
transcriptase real time PCR too. The challenge test revealed that all the non-luminescent strains were less virulent.
The most virulent strain of luminescent LMG21363 had a relative percentage survival (RPS) value of 25 and its non-luminescent counterpart had only 49 RPS which is statistically significant (p<0.05). Furthermore, the non-luminescent variants produced lower levels of the quorum sensing master regulator luxR and vhp (p<0.01). Moreover
the QS- mutant (non-luminescent) showed significantly higher RPS and lower gene expression (luxR and vhp) than
the QS+ mutant (luminescent). This study concludes that the non-luminescent variants of Vibrio harveyi and Vibrio
campbellii were less virulent than luminescent counterparts under in vivo conditions and produced lower levels of
some virulence genes.
