Antioxidant capacity, non-specific immunity, histopathological analysis and immune-related genes expression in Nile tilapia Oreochromis niloticus infected with Aeromonas schubertii

doi:10.1016/j.aquaculture.2020.735642

Aquaculture

Volume 529, 15 December 2020, 735642

https://doi.org/10.1016/j.aquaculture.2020.735642 Get rights and content

Highlights

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A. schubertii infection stimulated the activation of antioxidant activity and non-specific immunity in Nile tilapia.
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A. schubertii induced obvious histological changes in liver, spleen, head kidney, brain and intestine of Nile tilapia.
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A. schubertii triggered various immune-related genes in Nile tilapia.
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This is the first investigation of the host response to A. schubertii infection in a fish.

Abstract

Aeromonas schubertii is a conditional pathogen widely distributed in aquatic environments, yet it was only recently reported as a causative pathogen in fish. This study investigated antioxidant capacity, non-specific immunity, histopathology and immune-related gene expression profiles in Nile tilapia Oreochromis niloticus injected with A. schubertii. The results show that A. schubertii infection stimulated the activation of antioxidant activity and non-specific immunity in Nile tilapia. Histopathological analysis revealed that inflammation existed in the liver, spleen, head kidney, brain and intestine of the infected fish. Quantitative real-time PCR was performed to measure mRNA expression levels of six immune-related genes (interleukin-1β, tumor necrosis factor-α, cyclooxygenase-2, transforming growth factor beta, interleukin-10 and heat shock protein 70) in the intestine and head kidney at different timepoints after experimental infection. The results demonstrated clear transcriptional activation of these immune-related genes in the intestine and head-kidney tissues. To our knowledge, this is the first study to investigate the host response to A. schubertii infection in a fish. These results will contribute to further understanding of the pathogenesis and host defense system in fishes following infection with A. schubertii.

Introduction

Tilapia is the second-most-farmed fish globally after carp and has been cultured commercially in over 100 countries (Fitzsimmons and Watanabe, 2010). With dramatic increases in tilapia production, there have been increasing reports of disease outbreaks, which can cause serious economic losses in the tilapia industry. Many diseases have been reported in tilapia farming, such as caused by Streptococcus spp. (Verner-Jeffreys et al., 2018)，Aeromonas spp. (Dong et al., 2017; AlYahya et al., 2018; Ren et al., 2019), and virus (Tattiyapong et al., 2017). However, no disease affecting tilapia was attributed to Aeromonas schubertii infection until very recently, when Ren et al. (2019) reported the first case of A. schubertii infection in brackish water wild Nile tilapia Oreochromis niloticus in China.

Aeromonas spp. are widely distributed in aquatic environments (Hazen et al., 1978; Janda and Abbott, 2010). Members of this genus raise concern because of their potential to act as pathogens in humans as well as among diverse warm- and cold-blooded animals. A. schubertii is rarely reported as the cause of disease in aquatic animals, but it is a typical human–animal comorbidity pathogen (Liu et al., 2019). In humans, A. schubertii caused acute diarrhea (Howard and Buckley, 1985; Janda and Abbott, 2010); in aquatic animals, such as frogs (Pearson et al., 2000), shrimp (Yano et al., 2015) and mussels (Latif-Eugenin et al., 2016), it caused severe sepsis. Recently, A. schubertii was reported as a pathogen in fish (Chen et al., 2012; Liu and Li, 2012; Ren et al., 2019). As a result of increased breeding densities, the prevalence of A. schubertii is gradually increasing in aquatic environments, compounding the risks to fish farming (Kao and Kao, 2011). Until now, no in-depth research has been reported concerning the host defense mechanism of fish following A. schubertii infection. Changes in the expression levels of immune-related genes after pathogen infection are important indicators of immune response in fish, and examination of these immune-related genes will contribute to understanding the immune mechanisms both in Nile tilapia and in teleost fishes in general.

In this study, antioxidant capacity, non-specific immunity and histopathology were investigated in Nile tilapia following injection with A. schubertii. Additionally, the relative expression levels of some immune-related genes were determined to explore the immune responses of Nile tilapia. The results provide a better understanding of the immune response mechanisms to A. schubertii infection in teleost fishes.

Section snippets

Experimental design and bacteria preparation

A total of 270 Nile tilapia (average weight 20.53 ± 1.42 g, and average length 10.70 ± 0.27 cm) were provided by Baolu Aquatic Technology Co., Ltd., located in Ding'an County, Hainan Province, China. All fish were subjected to a two-week acclimatization period before bacterial challenge. During the acclimation period, the tilapia were maintained in continuously circulating aerated water (pH 7.5 ± 0.3, temperature 30 ± 1 °C, ammonia nitrogen <0.2 mg/L, and dissolved oxygen ≥5.5 mg/L) and fed

Antioxidant ability after injection with A. schubertii

The antioxidant capacity of Nile tilapia after intraperitoneal injection of A. schubertii was depicted in Fig. 1. SOD activity peaked at 12 hpi and the minimum activity occurred at 48 hpi (Fig. 1A). GSH-PX activity showed significant increases at 6 hpi, 12 hpi and 24 hpi, with the maximum level observed at 6 hpi (Fig. 1B). MDA activity was lowestat 12 hpi, then gradually increased by 24 hpi (Fig. 1C).

Non-specific immune responses after injection with A. schubertii

Fig. 2 depicted the non-specific immune responses in A. schubertii infected Nile tilapia. The

Discussion

The infection is a life-and-death struggle between host and pathogen, in which the host must mobilize all available resources to win (Sun et al., 2019a, Sun et al., 2019b). As vertebrate, teleost has non-specific and specific immune systems to response to bacterial infection. Therefore, bacterial infection has a significant effect on the expression of immune-related genes in teleost (Zhang et al., 2018). To help prevent outbreaks in tilapia and improve our understanding of A. schubertii

Ethics statement

All animals' treatments were strictly in accordance with the guidelines of Animal Experiment Ethics Committee of Hainan University. The protocol was approved by Animal Experiment Ethics Committee of Hainan University.

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgment

This study was funded by National Key R&D Program of China (No. 2019YFD0900105) and Project for upgrading key lab of tropical hydrobiology and biotechnology of Hainan Province (No. ZY2019HN0902).

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Antioxidant capacity, non-specific immunity, histopathological analysis and immune-related genes expression in Nile tilapia Oreochromis niloticus infected with Aeromonas schubertii

Highlights

Abstract

Introduction

Section snippets

Experimental design and bacteria preparation

Antioxidant ability after injection with A. schubertii

Non-specific immune responses after injection with A. schubertii

Discussion

Ethics statement

Declaration of Competing Interest

Acknowledgment

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