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Tenacibaculum maritimum can boost inflammation in Dicentrarchus labrax upon peritoneal injection but cannot trigger
Inês A Ferreira1,2,3, Paulo Santos1,2, Javier Sanz Moxó1
1Interdisciplinary Centre of Marine and Environmental Research (CIIMAR), University of Porto, Porto, Portugal.
Introduction:
Despite being a bacterial pathogen with devastating consequences, Tenacibaculum maritimum's pathogenesis is not fully understood. The aim of the present study was to elucidate if different inoculation routes (intraperitoneal - i.p - injection and bath challenge - known to induce mortality) can induce tenacibaculosis (i.e., using the same T. maritimum inoculum), as well as evaluate the short-term immune response of European sea bass (D. labrax). Additionally, the host response against i.p. injection of extracellular products (ECPs) was also studied.
Methods:
Fish were i.p. challenged with 5.5 × 105 CFU mL-1 of T. maritimum cells with or without ECPs (BECPs and BWO, respectively), ECPs alone or marine broth (mock). Another group of fish was bath-challenged with 5.5 × 105 CFU mL-1 to confirm the virulence of the bacterial inoculum. Undisturbed specimens were used as controls. The severity of both challenges was determined by following percentage survival. Blood, liver and head-kidney samples were collected at 0, 3, 6, 24 and 48 h post-challenge for assessing immune parameters, oxidative stress and gene expression. Total and differential peritoneal cell counts were performed. The presence of viable bacteria in the blood and peritoneal cavity was studied.
Results:
Symptoms of tenacibaculosis, such as skin/fin abrasions, were only observed in the bath-challenged fish, where 0% survival was recorded, whereas 100% survival was observed after i.p. injection of the same bacterial inoculum. An increase in total leukocyte numbers in the peritoneal cavity was observed 3 h post-injection of BECPs when compared to the other treatments. Blood total leukocytes, lymphocytes, and thrombocyte numbers dropped after the challenge, mainly in fish challenged with BECPs. At 48 h post-challenge, bactericidal activity in the plasma increased in fish injected with bacteria (with and without ECPs). The same tendency was seen for some of the oxidative stress parameters.
Discussion/Conclusions:
The increased expression of il1β, il6, il8, and hamp1 in fish challenged with ECPs and BECPs suggests a more exacerbated pro-inflammatory response in the head-kidney against these inocula. The infection trial and the observed immune responses showed that the infection route is a determinant factor regarding T. maritimum-induced pathogenesis in European sea bass.
Insights
The infection route significantly impacts Tenacibaculum maritimum pathogenesis in European sea bass. Bath challenges caused mortality, while intraperitoneal injections showed higher survival and modulated immune responses.
Area of Science:
- Aquatic Animal Health
- Fish Immunology
- Bacterial Pathogenesis
Background:
- Tenacibaculum maritimum is a significant bacterial pathogen in aquaculture.
- The pathogenesis and host immune response to T. maritimum are not fully understood.
- European sea bass (D. labrax) are susceptible to bacterial infections.
Purpose of the Study:
- To investigate the impact of different inoculation routes (intraperitoneal injection vs. bath challenge) on T. maritimum pathogenesis in European sea bass.
- To evaluate the short-term immune response of European sea bass to T. maritimum and its extracellular products (ECPs).
- To determine the role of ECPs in T. maritimum-induced disease.
Main Methods:
- European sea bass were challenged via intraperitoneal injection or bath with T. maritimum cells and/or ECPs.
- Survival rates were monitored to assess disease severity.
- Immune parameters, oxidative stress markers, and gene expression (il1β, il6, il8, hamp1) were analyzed in blood, liver, and head-kidney tissues at various time points post-challenge.
- Bacterial presence in blood and peritoneal cavity was investigated.
Main Results:
- Bath challenge with T. maritimum resulted in 0% survival, while intraperitoneal injection showed 100% survival.
- Intraperitoneal injection of ECPs increased peritoneal leukocytes, whereas BECPs (bacteria with ECPs) decreased blood leukocytes, lymphocytes, and thrombocytes.
- Plasma bactericidal activity and some oxidative stress parameters increased 48 hours post-injection with bacteria.
- Upregulation of pro-inflammatory genes (il1β, il6, il8, hamp1) was observed in head-kidney following ECP and BECP challenge.
Conclusions:
- The route of infection is a critical factor in T. maritimum pathogenesis in European sea bass.
- Intraperitoneal challenge with T. maritimum, especially with ECPs, elicits a significant inflammatory immune response.
- Understanding these route-dependent responses is crucial for developing effective disease control strategies in aquaculture.
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