DAO 121:149-159 (2016)  -  DOI: https://doi.org/10.3354/dao03043

Francisella noatunensis subsp. noatunensis invades, survives and replicates in Atlantic cod cells

Kathrine R. Bakkemo1, Helene Mikkelsen2, Audny Johansen3, Børre Robertsen4, Marit Seppola5,*

1PHARMAQ AS, 0213 Oslo, Norway
2The Northern Norway Regional Health Authority, 9019 Tromsø, Norway
3Nofima, 9291, Tromsø, Norway
4Norwegian College of Fishery Science, UiT - The Arctic University of Norway, 9037, Tromsø, Norway
5Department of Medical Biology, UiT - The Arctic University of Norway, 9037 Tromsø, Norway
*Corresponding author:

ABSTRACT: Systemic infection caused by the facultative intracellular bacterium Francisella noatunensis subsp. noatunensis remains a disease threat to Atlantic cod Gadus morhua L. Future prophylactics could benefit from better knowledge on how the bacterium invades, survives and establishes infection in its host cells. Here, facilitated by the use of a gentamicin protection assay, this was studied in primary monocyte/macrophage cultures and an epithelial-like cell line derived from Atlantic cod larvae (ACL cells). The results showed that F. noatunensis subsp. noatunensis is able to invade primary monocyte/macrophages, and that the actin-polymerisation inhibitor cytochalasin D blocked internalisation, demonstrating that the invasion is mediated through phagocytosis. Interferon gamma (IFNγ) treatment of cod macrophages prior to infection enhanced bacterial invasion, potentially by stimulating macrophage activation in an early step in host defence against F. noatunensis subsp. noatunensis infections. We measured a rapid drop of the initial high levels of internalised bacteria in macrophages, indicating the presence and action of a cellular immune defence mechanism before intracellular bacterial replication took place. Low levels of bacterial internalisation and replication were detected in the epithelial-like ACL cells. The capacity of F. noatunensis subsp. noatunensis to enter, survive and even replicate within an epithelial cell line may play an important role in its ability to infect live fish and transverse epithelial barriers to reach the bacterium’s main target cells—the macrophage.


KEY WORDS: Bacterial invasion · Gentamicin protection assay · Macrophages · Intracellular bacteria · IFNγ


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Cite this article as: Bakkemo KR, Mikkelsen H, Johansen A, Robertsen B, Seppola M (2016) Francisella noatunensis subsp. noatunensis invades, survives and replicates in Atlantic cod cells. Dis Aquat Org 121:149-159. https://doi.org/10.3354/dao03043

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