Virulence of luminescent and non-luminescent isogenic vibrios towards gnotobiotic <i>Artemia franciscana</i> larvae and specific pathogen-free <i>Litopenaeus vannamei</i> shrimp

Aims: This study was conducted to test the virulence of luminescent (L) and non-luminescent (NL) isogenic strains of Vibrio campbellii LMG21363, Vibrio harveyi BB120 (wild type) and quorum-sensing mutant strains derived from the wild type such as Vibrio harveyi BB152, BB170, MM30 and BB886.Methods and Results: The NL strains could be obtained by culturing rifampicin-resistant luminescent strains in the dark under static condition. The virulence of the L and NL strains was tested in gnotobiotic Artemia franciscana larvae challenged with 104 CFU ml-1 of bacteria. All luminescent isogenic tested strains showed higher virulence compared to the NL strains. The virulence of L and NL V. campbellii and V. harveyi BB120 was also tested in specific pathogen-free juvenile shrimp upon intramuscular injection with 106 CFU of bacteria. In contrast with Artemia, there was no significant difference in mortality between the groups challenged with L and NL strains (P > 0·05). The non-luminescent strains were not able to revert back to the luminescent state and quorum sensing did not influence this phenotypic shift.Conclusions: Luminescent Vibrio strains can switch to a non-luminescent state by culturing them in static conditions. The NL strains become less virulent as verified in Artemia.Significance and Impact of the Study: The luminescent state of Vibrio cells in a culture needs to be verified in order to assure maintenance of virulence.