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Diseases of Aquatic Organisms

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DAO 45:45-52 (2001)  -  doi:10.3354/dao045045

Lactococcus garvieae infection in the giant freshwater prawn Macrobranchium rosenbergii confirmed by polymerase chain reaction and 16S rDNA sequencing

Shih-Chu Chen1,*, Yu-De Lin1, Li-Ling Liaw2, Pei-Chi Wang1

1Department of Veterinary Medicine, National Pingtung University of Sciences and Technology, Pingtung 912, Taiwan, ROC
2Culture Collection and Research Center, Food Industry Research and Development Institute, Hsinchu 300, Taiwan, ROC

ABSTRACT: 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 LD50 value of isolate MR1 was 6.6 x 105 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

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