Pathogenicity and colonization of Litopenaeus vannamei larvae by luminescent vibrios

The virulence of the bacterial strains CAIM 333 and CAIM 372 identified as Vibrio campbellii and strain CAIM 79, identified as V. harveyi, were evaluated using bioassays with Litopenaeus vannamei larvae at bacterial densities of 105 CFU ml− 1. There was no difference in virulence observed between the two strains of V. campbellii. The shrimp zoea stages were more susceptible to the CAIM 333 strain. L. vannamei larvae did not show any susceptibility to the bacterial strain CAIM 79. No statistical correlation (P > 0.05) was found between the number of CAIM 333 and CAIM 79 bacteria inoculated and ingested (inside the digestive tract), and no statistical correlation (P > 0.05) was found between number of CAIM 333 bacteria ingested and shrimp larval mortality. The colonization process begins in the oral region, followed by the cephalotorax and then the inside the MGT. A 2 h exposure experiment (Exp-2 h) proved to be better to evaluate the colonization process when compared to a 24 h exposure method.