Photobacterium damselae subsp. piscicida Is Capable of Replicating in Hybrid Striped Bass Macrophages

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The purpose of this study was to use an in vitro assay to evaluate the ability of Photobacterium damselae subsp. piscicida to survive and replicate within macrophages obtained from hybrid striped bass (striped bass Morone saxatilis x white bass M. chrysops). The results indicated that the number of bacteria recovered from macrophages after 3, 6, 12, and 18 h of incubation increased significantly from time 0 (105, 510, 1,091 and 1,385%, respectively). Replication of the intracellular bacteria was observed at a very low multiplicity of infection (1 bacterium to 100 macrophages). In contrast, the number of Escherichia coli recovered from macrophages declined 47, 80, 91, and 96%, respectively. Light and electron microscopy confirmed the internalization, uptake, and multiplication of bacteria within spacious, clear vacuoles in the macrophages. Using acid phosphatase as a lysosomal marker, we provide evidence that P. damselae subsp. piscicida inhibits phagolysosomal fusion. This study demonstrates that P. damselae subsp. piscicida is a very successful facultative, intracellular pathogen that can survive and multiply within hybrid striped bass macrophages.

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Journal of Aquatic Animal Health

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