Investigations of melatonin influences on mink resistances to Pseudomonas aeruginosa

Melatonin is a potent immunomodulator with anti-inflammatory and antioxidant effects that significantly reduces inflammation. In practice, the subcutaneously implanted melatonin in minks is generally used to stimulate molting in autumn in advance, thereby reducing feed cost to obtain considerable economic benefits. The opportunistic Pseudomonas aeruginosa (P. aeruginosa) infection causes hemorrhagic pneumonia, massive mortality and economic losses in minks, while melatonin treatments to minks could improve host resistance; therefore, the objective of our study is to investigate the relationships of the susceptible infections caused by P. aeruginosa with the improved immunity by melatonin in minks. In this study, 1 × 10⁹ colony forming units of P. aeruginosa were used to infect 12 minks in the case group (IGM group) after 10 mg melatonin dosage per body weight (kg) treatment under the implantation in mink ears. The control group (IG group) contains 12P. aeruginosa infected minks without melatonin treatments. In the meantime, another 24 minks were also included in our study with no P. aeruginosa infections, where 12 of them were treated with melatonin for comparisons. The results showed that melatonin treatments increased mink immunity and resistance to P. aeruginosa infections, alleviated the pathogenesis and pathological lung damages, and enhanced the lung scavenging abilities. The lung indexes of minks after melatonin treatments significantly decreased comparing IGM group with IG group (P < 0.01). Similarly, the bacterial loads of minks in the IGM group were significantly lower than those in the IG group at different infected time points (P < 0.05). In addition, the concentration levels of tumor necrosis factor α (TNF-α) significantly increased after melatonin treatments (P < 0.05). In conclusion, our study explored the relationships between P. aeruginosa infection and host resistance in minks, and provided valuable understandings of the pathogenesis of mink hemorrhagic pneumonia and the potential applications of melatonin in the future practical treatments.