Abstract. Granulomatous hepatopancreatitis of unknown etiology has been considered an important disease of Texas shrimp mariculture since 1985. Samples of Pacific white shrimp (Penaeus vannamei) were collected during 1986, 1987, and 1990 from three farms and an experimental mariculture facility with histories of production loss and increased mortality rates. Histologic and ultrastructural examination of shrimp from the four sites demonstrated two morphologically distinct, Gram-negative, double-enveloped, intracytoplasmic bacteria in necrotic hepatopancreatic epithelium. The more numerous small, pleomorphic rod as well as the helical organism are both taxonomically unclassifiable. The helical organism lacked ultrastructural characteristics of previously described helical or spiral bacteria. The relationship between the two organisms is unknown, but the pleomorphic rod is thought to play a major role in the disease. The role of a bacterial agent(s) in subsequent disease episodes is suggested by the observation that the use of oxytetracycline-medicated feed resulted in increased production and survival. Hepatopancreatic tubular epithelial necrosis and shrimp mortality correlated directly with the extent of infection by the small pleomorphic rod. Individual discrete bacteria were identified microscopically by Steiner and Steiner's method. Three major developmental stages of the disease were characterized based on the extent and number of hepatopancreatic tubular epithelial cells containing bacteria, the degree of tubular interstitial inflammation, and the extent and chronicity of tubular necrosis. Additional studies are needed to clarify the roles of the different bacteria identified and the potential role of environmental factors on the disease process.
Streptococcus shiloi strains, including the type strain, which were isolated in Israel and the United States, and Streptococcus iniae ATCC 29178T (T = type strain) are phenotypically identical (as determined with API 20 STREP and API 50CH kits; beta-hemolytic on sheep blood agar). DNA-DNA hybridization experiments revealed levels of homology of 77 to 100%. Thus, S. shiloi should be considered a junior synonym of S. iniae. This bacterium is a major fish pathogen that is distributed worldwide.Streptococcus iniae was described in 1976 by Pier and Madin (7), who isolated this bacterium from skin lesions of a captive Amazon freshwater dolphin (Inia geofiensis). In 1994, we described a new streptococcal species that was isolated from diseased rainbow trout (Onchorynchus mykiss) in Israel and was named Streptococcus shiloi (2). This name was validated in 1995 (4). S. shiloi differed from S. iniae in G + C content (37 mol% [2]; the G + C content of S. iniae is 32.9 mol% [7]), pathogenicity and host range. S. shiloi was shown to be the etiologic agent of an acute meningoencephalitis that affects trout (3), and it was also shown to be the causative agent of a similar disease in tilapia (Oreochromis aurea X Oreochromis nilotica hybrids) along with Streptococcus dificile (2). S. shiloi and S. dificile were shown to have broad geographical distributions and broad host ranges (2). S. shiloi was also isolated from diseased tilapia in Taiwan and the United States, and S. dificile was isolated in Japan from sea-cultured yellowtails (Seriola quinqueradiata) (2).The purposes of this work were to elucidate the taxonomic position of S. shiloi and to compare S. shiloi Israeli field isolates collected over the last 5 years with isolates collected in the United States during the last 2 years.A total of 15 American isolates were compared with 19 Israeli isolates, including the type strain of S. shiloi (strain ND 2-16 [= CIP 103769]), 1 strain isolated in Taiwan, and S. iniae ATCC 29178T (T = type strain) ( Table 1). All of the strains were isolated from diseased fish. The type of hemolysis was determined on Columbia agar base (Difco) supplemented with 5% (vol/vol) defibrinated sheep blood; the type of hemolysis produced on this medium was then compared with the type of hemolysis produced on the same medium supplemented with human or bovine blood. Biochemical reactions were determined with API 20 STREP and API 50CH systems (API, La Balmes Les Grottes, France). Most of the instructions of the manufacturer were followed; the only exception was the temperature of incubation, which was adjusted to 30°C. Results were read after 24 h of incubation. DNA was extracted by a previously described method (2). DNA-DNA hybridization experiments were performed by using the hy- l), except that the volumes used were modified (2). After denaturation by boiling, reassociation was allowed to proceed for 18 h at 60°C. Duplicate reactions were performed, and each run was performed twice. The levels of DNA relatedness (relative binding ratios) and the differe...
ABSTRACT. We isolated for the first time Streptococcus iniae strains associated with diseased marine fish. Diseased red drum Sciaenops ocellatus were lethargic, and presented external signs (exophthalmia and loss of orientation) resembling those of freshwater fish infected by S. injae. Skin lesions, extending to a necrotizing myositis, were typical of S. iniae infection of red drum. Histopathological findings indcate that S. iniae infection in red drum produces a chronic disease with systemic involvement characterized by multiple necrotic foci. Molecular epidemiology (RFLP [restriction fragment length polymorphism] ribotyping) revealed that 2 different ribotypes were involved in a single outbreak. The first is the EcoRl 'Israeli' trout and tilapine ribotype (Hind111 type a strains), while the second is the EcoRI 'American' ribotype (Hind 111 type b strains), typical of tilapines farmed in Texas and Idaho.
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