An epizootic bacterial infection in the giant freshwater prawn Macrobranchium rosenbergii occurred in Taiwan from May to June 1999. The cumulative mortality was approximately 30 to 75%. The diseased prawns showed opaque and whitish muscles and were approximately 2 mo old with total lengths from 5 to 6 cm. Histopathologically, they showed marked edema and necrotic lesions with inflammation in the muscles and hepatopancreas. Bacteria isolated using brain heart infusion medium or tryptic soy agar were Gram-positive and ovoid. Three isolates from diseased prawns at different farms were tested using the API 20 Strepsystem and conventional tests and identified as Lactococcus garvieae. Experimental infections with these isolates gave gross signs and histopathological changes similar to those seen in the naturally infected prawns. The LD 50 value of isolate MR1 was 6.6 × 10 5 colony forming units/prawn. Identification of MR1 was confirmed by a PCR assay for L. garvieae that gave the expected amplicon of 1100 bp. In addition, its 16S rDNA sequence (GenBank accession number AF283499) gave 99% sequence identity to Enterococcus seriolicida (synonym L. garvieae; GenBank accession number AF061005). This is the first report of confirmed L. garvieae infection in prawn aquaculture. KEY WORDS: Lactococcus garvieae · Giant freshwater prawn · Macrobranchium rosenbergii · PCR · 16S rDNA sequencing Resale or republication not permitted without written consent of the publisherDis Aquat Org 45: [45][46][47][48][49][50][51][52] 2001 ola quinqueradiata in Japan was named Enterococcus seriolicida (Kusuda et al. 1991) after previously being classified as Streptococcus (Kusuda et al. 1976). However, taxonomic studies based on DNA-DNA hybridization (Eldar et al. 1996) and sequence analysis of 16S rRNA (Domenech et al. 1993) indicated E. seriolicida (Kusuda et al. 1991) was synonymous with L. garvieae (Eldar et al. 1996). In Spain, a serious septicemic disease of Scopthalmus maximus or large turbot (100 g to 3 kg) was accredited to an Enterococcus-like bacterium (Nieto et al. 1995) that was also found to match with L. garvieae (Eldar et al. 1996). Zlotkin et al. (1998) subsequently developed a polymerase chain reaction (PCR) assay based on unique regions of the L. garvieae 16S rRNA gene that allow for its specific identification.The giant freshwater prawn Macrobranchium rosenbergii is commercially cultured throughout the world and intensively so in Taiwan, where production, however, decreased by 47 to 52% from 1992 to 1995 (New 1995, Taiwan Fisheries Bureau 1996 due to disease problems. Two diseases have been linked to production decline. One is a yeast infection that occurs mostly in the cool season (October to March), with symptoms including a yellow exoskeleton, a swollen hepatopancreas (HP), milky hemolymph and opaque and whitish muscles (Shu 1993, Cheng & Chen 1998a. The other is an Enteroccoccus-like infection that occurs mostly in the hot season (June to September, especially during phytoplankton blooms) and causes muscle ...

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From May to August 2001 in Taiwan, 27 farms for the giant freshwater prawn Macrobrachium rosenbergii experienced white tail disease outbreaks in animals approximately 3 to 5 mo old, with total lengths from 6 to 8 cm. Examination of the infected prawns revealed not only previously reported Lactococcus garvieae (16 farms) but also the novel L. lactis subsp. lactis (10 farms). One farm had shrimp infected with both bacteria. In the farms with L. lactis infections, the cumulative mortality was approximately 25 to 60%. Gross signs of disease were opaque and whitish muscles, while histopathology included marked edema and necrotic lesions, with inflammation in the muscles and hepatopancreas. Bacteria isolated using brain/heart infusion medium or tryptic soy agar were Gram-positive and ovoid. Eleven isolates from different farms were identified as L. lactis subsp. lactis using API 20 Strep and Rapid ID32 Strep tests and using PCR assays specific for the L. lactis subsp. lactis 16S rDNA gene (650 bp amplicon) and for the 16S to 23S rDNA interspacer region (380 bp amplicon). In addition, sequencing of the full 16S rDNA genes of 2 of the isolates (MR17 and MR26; GenBank Accession Numbers AF493058 and AF493057, respectively) revealed 99.9% identity between the isolates and 98.7% identity to several complete 16S rRNA sequences of L. lactis subsp. lactis at GenBank. Experimental infections with our isolates gave gross signs and histopathological changes similar to those seen in naturally infected prawns. The mean lethal dose of 4 isolates and the reference strain L. lactis subsp. lactis BCRC 10791 ranged from 4.2 × 10 6 to 2.5 × 10 7 colony-forming units prawn -1 , indicating virulence similar to that previously reported for L. garvieae. This is the first report confirming L. lactis subsp. lactis as a pathogen in juvenile and adult prawns from aquaculture.KEY WORDS: Lactococcus lactis subsp. lactis · Giant freshwater prawn · Macrobrachium rosenbergii · PCR · 16S rDNA sequencing · 16S to 23S rDNA interspacer regions gene Resale or republication not permitted without written consent of the publisherDis Aquat Org 79: [9][10][11][12][13][14][15][16][17] 2008 molymph and opaque or whitish muscles (Shu 1993, Chen et al. 2003, and a Lactococcus garvieae infection that occurs principally in the hot season (June to September, especially during phytoplankton blooms) and causes muscle necrosis (Cheng & Chen 1988a,b, Chen et al. 2001. Streptococcus lactis, recently reclassified as Lactococcus lactis, is not recognized as a common veterinary pathogen, but it has occasionally been reported in the etiology of cattle mastitis and in septic arthritis of the neonatal calf (Wichtel et al. 2003). L. lactis is considered to be a skin commensal, and cattle are natural hosts. Although rare, human infection with L. lactis was first reported by Ledger et al. (1974). It has since been reported as a cause of endocarditis (Mannion & Rothburn 1990, Clark & Burnie 1991, arthritis (Campbell et al. 1993) and septicemia in an immunocompromised ...