Colonização de tecidos e líquido corpóreo do camarão litopenaeus vannamei por vibrio parahaemolyticus autóctone do ambiente de cultivo

Abstract

Shrimp farming activity in Northeast Brazil has been threatened by viral and bacterial diseases outbreaks. In a world scale, since 2009, shrimp farms have been emerging from an emerging disease known as "acute hepatopancreatic necrosis disease" (AHPND), with V. parahaemolyticus as the etiological agent. This infection has attracted the attention of farmers because of the high mortality rates recorded in shrimp larvae. Invasion routes of this pathogen in Litopenaeus vannamei shrimp tissues are not very clear, and their understanding is a fundamental part for the comprehension of its pathogenic mechanisms, as much as for contributing to the elaboration of strategies in order to prevent the further outbreaks. Thus, the objective of this study was to monitor interactions of V. parahaemolyticus in the hemolymph and young tissues of L. vannamei shrimp. In order to proceed with this, a strain of V. parahaemolyticus was used, in oral invasion bioassays, in young L. vannamei shrimps. Microbiological and microscopic analyzes of fluid and tissue samples were performed. Samples were taken at 0, 24, 48 and 72 h after inoculation. Presence of bacteria of the Vibrio genus in the hemolymph was not detected by the counts with Thiosulfate Citrate Bile Sucrose (TCBS) medium for the animals from the negative and experimental control tanks. Counts of Vibrio spp. were detected in hepatopancreas samples from negative and experimental control tanks: (0h: 2.2 logCFU / g and 24h: 0.6 logCFU / g); (0h: 0.3 logCFU / g and 48h: 1.1 logCFU / g) and for intestine samples (24h: 1 logCFU / g); (0h: 0.7 logCFU / g and 24h: 0.6 logCFU / g). Count of V. parahaemolyticus resulted in the detection of the bacterium in hepatopancreas tissues (48h: 0.7 logCFU / g and 72h: 0.8 logCFU / g) and medium intestine (72h: 0.7 logCFU / g) for challenge experiment. By microscopic analysis, we observed a consistency between plaque counts and bacterial presence in tissues. Tissue colonization by V. parahaemolyticus occurred in a differentiated way, with fixation at first in the tissues of the midgut followed by a more intense tissue installation in the hepatopancreas. From this protocol, other possibilities and approaches become viable using V. parahaemolyticus as an indicator. A good example is the possibility of monitoring colonization of the organism, and a parallel analysis of the immunological mechanisms of shrimp favoring the development of technologies in order to prevent or treat vibriosis events in shrimp culture.