Effects of dietary heat-killed Pseudomonas aeruginosa strain VSG2 on immune functions, antioxidant efficacy, and disease resistance in Cyprinus carpio
2020
Giri, Sib Sankar | Jun, Jin Woo | Yun, Saekil | Kim, Hyoun Joong | Kim, Sang Guen | Kim, Sang Wha | Woo, Kang Jeong | Han, Se Jin | Oh, Woo Taek | Kwon, Jun | Sukumaran, V. | Park, Se Chang
A probiotic strain of Pseudomonas aeruginosa VSG2 was previously isolated from the gut of Indian major carp Labeo rohita. But, its efficacy as a heat-inactivated probiotic on the immune response of fish remains unexplored. Thus, present study investigated the effect of heat-killed P. aeruginosa VSG2 (HK-PA) supplementation on the immune function, digestive enzymatic activities, and antioxidant status of Cyprinus carpio. Moreover, the effect of HK-PA supplementation on the susceptibility of C. carpio to Aeromonas hydrophila challenge was also evaluated. To do so, diets containing five different concentrations of HK-PA (mg kg⁻¹) (0 [basal diet], 10 [PA10], 20 [PA20], 30 [PA30], and 40 mg kg⁻¹ [PA40]) were fed to fish for 8 weeks. The results revealed that immune-related factors, such as lysozyme, protein level, alkaline phosphatase, and alternative complement pathway levels increased in fish fed with HK-PA, but differences were significant in PA20–PA40 compared to the control. The immunoglobulin level was higher (p < .05) in PA30, compared to the control. Superoxide dismutase (SOD), glutathione, glutathione peroxidase (GPx), and myeloperoxidase levels significantly increased in serum or skin mucus of fish fed with HK-PA. Accordingly, malondialdehyde levels decreased in fish fed with HK-PA. Among intestinal enzymatic activities, protease activity was higher in the HK-PA fed groups compared to the control. Moreover, mRNA expression of antioxidant genes (SOD, GPx, and catalase) significantly increased in the liver of PA20–PA40. Fish in the PA30 exhibited the highest relative post-challenge survival (71.54 ± 5.37%) against A. hydrophila infection. Overall, dietary administration of HK-PA at 30 mg kg⁻¹ (PA30) for 8 weeks improved (p < .05) the skin mucosal and serum immune parameters, strengthened antioxidant capacity, enhanced intestinal enzymatic activities, and increased the resistance against a pathogen challenge. The heat-killed P. aeruginosa VSG2 represents a promising dietary supplement for carps in aquaculture.
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