Comparison of Virulence between Luminescent and Non-Luminescent Vibrio harveyi and Vibrio campbellii in vivo

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.