Detection and identification of virulent Yersinia ruckeri: the causative agent of enteric redmouth disease in rainbow trout [Oncorhynchus mykiss] cultured in Fars province, Iran

From the winter 2002 to spring 2006, 126 moribund rainbow trout with clinical signs of external body haemorrhages around and within the oral cavity were sampled from 10 rainbow trout farms situated in the northwest and west of Fars province, Iran and examined for the detection and identification of Yersinia ruckeri, the causative agent of enteric redmouth disease. Fish kidneys were cultured aseptically on brain heart infusion [BHI] agar plates and incubated at 25°C for 48 h. Using conventional biochemical tests, Y. ruckeri was detected in 7 fish [5.5% of total fish sampled]. This was also confirmed using specific polymerase chain reaction [PCR] assay. The 16S rDNA PCR assays produced amplicons of 409 bp when applied to Y. ruckeri isolates as well as a reference strain. Results of antibiogram tests on Y. ruckeri isolates showed a high susceptibility to enrofloxacin, norfloxacin, ofloxacin, trimethoprim and oxytetracycline. In pathogenicity tests, dilution of 4 x 10[8] colony forming unit/ml of Y. ruckeri by immersion route in challenge experiments showed 70 +/- 8.2% mortality during 14 days post-infection. Experimentally infected fish showed typical haemorrhages in mouth, blackening of skin, exophthalmia and a wide haemorrhages on the internal organs

Aislamiento de Aeromona hydrophila en trucha Arcoiris (Oncorhynchus mykiss) / Isolation of Aeromona hydrophila in rainbow trowt (Oncorhynchus mykiss). Case report

Se realizó un muestreo en una granja piscícola dedicada a la explotación de trucha Arcoiris (Oncorhynchus mykiss), ubicada en el Estado de México, México, en el cual hubo un brote de septicemia hemorrágica provocada por el agente etiológico Aeromona hydrophila. Los animales presentaban oscurecimeinto de la piel, exoftalmina unilateral y el patrón de comportamiento alterado, la morbilidad fue del 80 por ciento y la mortalidad del 51.2 por ciento. Se llevaron a cabo estudios de histopatología y se encontró lesiones en intestino anterior, con hiperplasia del epitelio de las vellosidades, En encéfalo (cerebro medio) hubo congestión leptomeningea moderada difusa y en ojo se apreciaron focos de trombosis y reacción inflamatoria constituida por monocitos en la región periesclerótica y epitelio corneal. Se realizó estudio bacteriológico a partir del hígado de truchas Arcoiris afectadas, de donde se aisló A. hydrophilia, corroborándose las lesiones y el cuadro clínico antes descritos con la presencia del agente