Susceptibility of meagre (Argyrosomus regius Asso, 1801) to Photobacterium damselae subsp. piscicida
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1
MARE - Marine and Environmental Sciences Centre, ESTM, Polytechnic Institute of Leiria, Portugal
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2
CIIMAR, Interdisciplinary Centre of Marine and Environmental Research, Portugal
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3
Moredun Research Institute, United Kingdom
Photobacterium damselae subsp. piscicida (Phdp) is a gram-negative bacterium known to cause photobacteriosis in several fish species. It is considered as one of the most threatening pathogens, causing great losses in aquaculture. It is known that Phdp can cause important losses in meagre (Argyrosomus regius), however no study of the infection has been done in this fish species. The current study aimed to develop a Phdp infection protocol for A. regius. Preliminary trials were designed to evaluate the dose which causes death to 50% of the population (LD50). In a second trial, the development of the disease, including the fate that bacteria would have had in the fish by PCR analysis targeting the 16s RNA gene of Phdp, as well as host responses to infection in terms of both fish hematological levels (e.g. hemoglobin concentration, erythrocytes and leucocytes count) and humoral immune parameters (e.g. plasma lysozyme, alternative complement pathway and anti-trypsin activities). A model of cohabitation was used during 15 days, exposing healthy subjects with infected ones (injected with a concentration equal to LD50 previously calculated). During the course of the second trial, blood and fish organs (i.e. gills, liver, spleen, kidney and anterior intestine) were sampled at 0, 3, 6, 9, 12, 24, 48, 72 and 360 hours after infection. It was confirmed the virulence of the Phdp strain AQP 17.1 on A. regius individuals with an average weight of 28.3 ± 10.9 g, being the LD50 2.29×10^5 CFU ml-1, presenting infected fish, typical symptoms of the disease in the chronic state. The cohabitation model used in the second trial confirmed to be successful since individuals with an average weight of 23.4 ± 8.6 g were infected by cohabitation. The results suggest that the gills may have been one of the pathogen’s main entry sites into the host, spreading after 24 hours to the kidney and intestine. Phdp induced an innate immune response in A. regius that was evaluated in a time course basis. Both the number of blood leucocytes and the activity of the humoral immune parameters increased after 24 hours correlating with the invasion of the pathogen into organs such as the anterior intestine and the kidney. Phdp can induce a state of infection in A. regius through a cohabitation model, invading the organs of the host in a short time period, triggering the activity of the innate immune system.
Acknowledgements
This study had the support of Fundação para a Ciência e Tecnologia (FCT), through the strategic project UID/MAR/04292/2013 granted to MARE.
Keywords:
Cohabitation model,
Hematology,
Humoral immune parameters,
LD50,
Bacteria infection
Conference:
IMMR | International Meeting on Marine Research 2016, Peniche, Portugal, 14 Jul - 15 Jul, 2016.
Presentation Type:
Poster presentation
Topic:
Aquaculture
Citation:
Galhano
FF,
Cristóvão
MS,
Costas
B,
Costa
J,
Machado
M,
Azeredo
R,
Morais
H,
Anjos
CM,
França
M and
Baptista
TM
(2016). Susceptibility of meagre (Argyrosomus regius Asso, 1801) to Photobacterium damselae subsp. piscicida.
Front. Mar. Sci.
Conference Abstract:
IMMR | International Meeting on Marine Research 2016.
doi: 10.3389/conf.FMARS.2016.04.00043
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Received:
13 May 2016;
Published Online:
13 Jul 2016.
*
Correspondence:
Mr. Fábio F Galhano, MARE - Marine and Environmental Sciences Centre, ESTM, Polytechnic Institute of Leiria, Peniche, 2520-641, Portugal, fabioandrefg@gmail.com