Lactococosis en pseudoplatystoma reticulatum

Abstract

La lactococosis fue reportada a nivel mundial en numerosas especies de peces, ocasionando elevadas pérdidas económicas. seudoplatystoma reticulatum es una especie autóctona del río Paraná muy apreciada para el consumo, por lo cual la evaluación de las patologías en los cultivos intensivos es importante. Las muestras obtenidas en este trabajo corresponden a ejemplares juveniles provenientes de una piscicultura de la región nordeste argentina donde se registró una mortandad aguda. Los ejemplares afectados fueron anestesiados y sacrificados. Se realizó la ablación del hígado y secciones del órgano fueron empleadas para improntas. Pequeños trozos se colocaron en medio de cultivo Reinforced Clostridial Medium (Difco) y fueron incubados. El medio decultivo crecido se sembró por estriado en placas conteniendo medio de Man Rogos y Sharpe agar (MRS Merck), cultivándose durante 24 a 48 h. Los microorganismos obtenidos se sometieron a pruebas bioquímicas para determinar su ubicación taxonómica. Fragmentos de branquias, hígado, bazo, tubo digestivo y riñón fueron fijados en solución de Bouin, posteriormente fueron deshidratadas e incluidas en parafina. Los cortes histológicos se colorearon con Hematoxilina-Eosina, PAS y Giemsa. Se encontraron lesiones hemorrágicas en distintos puntos del tegumento, presencia de líquido ascítico y numerosas lesiones puntiformes en hígado. En las improntas y pruebas bioquímicas se detectaron cocos Gram positivos aislados, en diplos o en cadenas cortas, catalasas negativas e incapaces de reducir nitratos y sintetizar triptófano a partir de indol. En el hígado se observó predominio de alteraciones vasculares, fundamentalmente hemorrágicas de marcada intensidad. En el bazo se observaron intensas alteraciones vasculares, con predominio congestivo y hemorrágico. Las características clínicas de las lesiones, las pruebas bioquímicas y el diagnóstico histopatológico permiten atribuir la mortandad a Lactococcus garvieae.

Lactococcosis is reported worldwide in numerous fish species causing heavy financial losses. Pseudoplatystoma reticulatum is a native species of Paraná River, edible and highly appreciated in the region, so the consideration of diseases in intensive crops is important. In this work we present a high mortality case of P. reticulatum juveniles from a farm located in Northeastern Argentina. For this purpose, animals with symptoms were euthanized and the head was removed. Liver was collected and sections of the organ were used for histopathology. Small pieces were placed in tubes containing Reinforced Clostridial Medium (Difco) and then incubated. Cultures with microorganisms were incubated on plates containing Man Rogosa and Sharpe agar (MRS Merck) during 24 to 28 h. The colonies obtained were restrocked and kept refrigerated at -20°C in media containing glycerol at 20%. Cultured microorganisms were submitted to various biochemical tests to determine their taxonomy. Samples of gills, liver, spleen, gastrointestinal tract and kidney were fixed in Bouin’s solution and then dehydrated and embedded in paraffin. Histological sections were stained with Hematoxylin-Eosin, PAS and Giemsa. Hemorrhagic lesions were found in different parts of the tegument, and presence of ascites and numerous punctuate lesions in the liver were observed. In the imprints and biochemical tests of isolates Gram positive cocci were isolated, in diplos or short chains, that were negative catalase test and unable to reduce nitrate and synthesize tryptophan from indol. In the liver it was observed predominance of vascular alterations, mainly hemorrhagic of high intensity. Bacterial invasion stood out with predominantly peripheral location. In the spleen intense vascular alterations were observed with congestive and hemorrhagic dominance. It can be concluded according to the clinical characteristics of lesions, biochemical tests and histopathological diagnosis that mortality of fishes was due to Lactococcus garvieae.