Streptococcus iniae type II infections in rainbow trout Oncorhynchus mykiss

Abstract

Clinical and pathological findings (anorexia, hemorrhage, lethargy, loss of orientation and exophthalmia) indicated that Streptococcus iniae type II is responsible for a fatal disease in rainbow trout. Histopathological findings revealed that S. iniae type II produces a systemic disease, including a diffuse necrotizing myositis. The distribution of viable bacteria in infected tissues substantiated the pathological findings, confirming that S. iniae type II is responsible for a generalized septic disease of rainbow trout. KEY WORDS: Rainbow trout · Streptococcus iniae · Serotype · Pathology Resale or republication not permitted without written consent of the publisherDis Aquat Org 62: [177][178][179][180] 2004 2003). In the present work we assessed the pathological outcomes of infections of rainbow trout by S. iniae serotype II. Our results indicate that Serotype II strains produce an acute septic disease accompanied by multisystem organ involvement. MATERIALS AND METHODSSampling procedure for pathology and bacteriological analysis. Specimens were collected from 2 trout farms located in northern Israel (Upper Galilee) which are supplied with water at a constant temperature of 16°C. At the time of collection both farms were experiencing heavy mortalities, and bacteriological examination (30 fish from each farm, 50 to 350 g each) revealed pure colonies of β-hemolytic Gram-positive cocci. Bacteriological identification (Eldar et al. 1995), authenticated by PCR analysis (Zlotkin et al. 1998), confirmed the presence of arginine dehydrolase-negative isolates of Streptococcus iniae. PCR analysis with the p14 primer did not produce the 750 bp band, indicating that all current isolates were of type II (Bachrach et al. 2001). Tissues (brain, heart, spleen, kidney, liver, intestine, gills and muscle) from 10 diseased rainbow trout were fixed in 10% neutral buffered formalin and stained with hematoxylin and eosin (HE). Gross lesions were recorded.Distribution of bacteria in tissues. Bacterial colonyforming units (CFUs) were counted in the tissues of 20 rainbow trout (100 to 200 g each), infected with Streptococcus iniae type II and showing clinical signs of streptococcosis (darkening of the skin combined with multifocal ecchymoses, lethargy, loss of orientation and ocular pathologies). Organs (brain, heart, spleen, kidney, liver, intestine, gills and muscle) were weighed and blended over a 60-mesh grid. Tissue homogenate samples (1 g) were suspended in 10 ml phosphatebuffered saline (PBS) (15 mM Na 2 HPO 4 , 145 mM NaCl, pH 7.20) supplemented with 0.2% Triton X-100 (Sigma) and serially diluted. The bacterial CFU population was determined by plate counting.The bacterial loads in tissues of rainbow trout infected by Streptococcus iniae type I were assessed with a 2-step cohabitation method. First, 10 naive rainbow trout (50 to 80 g each) were infected by intraperitoneal inoculation of (7.5 × 10 5 CFU fish -1 ) virulent S. iniae Dan-15 (type I strain), as described previously (Eldar et al. 1997a). Then, on Day 10 ...

Rapid identification of pathogenic streptococci isolated from moribund red tilapia (Oreochromis spp.)

“…These alterations are indicative of a systemic infection, which is supported by the isolation of bacteria from various fish tissues. Myositis of the skeletal muscles was observed, and this was also reported in the case of S. iniae infection (Lahav et al, 2004). The presence of bacterial aggregations suggestive of streptococci was observed in the histological sections, which was consistent with the results obtained by Zamri-Saad et al (2010) in red tilapia naturally infected by S. agalactiae.…”

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“…Streptococcus iniae (S. iniae) is a hemolytic, gram-positive coccus firstly isolated in 1976 from a subcutaneous abscess of a captive freshwater dolphin (Inia geoffrensis) (Pier and Madin, 1976). Also, it has been reported in a number of species of fish, such as barramundi (Lates calcarifer) (Creeper and Buller, 2006), Nile tilapia (Oreochromis niloticus) (Shoemaker et al 2001) and rainbow trout (Oncorynchus mykiss) (Lahav et al, 2004) as well as in mammals (Pier andMadin, 1976 andFacklam et al, 2005). In rainbow trout, streptococcosis is characterized by a subacute to acute course, with specific lesions of panophthalmitis and meningitis beside minor pathological changes in other organs (Eldar and Ghittino, 1999).…”

Host-Directed Evolution of a Novel Lactate Oxidase in Streptococcus iniae Isolates from Barramundi ( Lates calcarifer )

“…Clearly, carbohydrate metabolism in bacteria is highly complex and will be affected by multiple factors including nutrient availability, exopolysaccharide production, oxygen availability, and other factors; thus, this area requires substantial further expert investigation using highly controlled culture environments. Moreover, S. iniae is a highly diverse species (14,23), and variability in growth characteristics should be expected. However, our preliminary experiments suggest that the type 2 enzyme may provide a competitive advantage under conditions where the lactate concentration is high.…”