Aeromonas hydrophila
infection represents a major impediment to the development of aquaculture, leading to important economic losses. Over the last few years, different methods have been used to counteract and minimize the negative effects of this
infection, such as the use of Melaleuca alternifolia
essential oil, popularly known as
tea tree oil (TTO), that possess a bactericide action against A. hydrophila. The purinergic system develops an important role in the inflammatory response, principally due to involvement of
adenosine triphosphate (
ATP) in the inflammatory process, as well as by the anti-inflammatory properties of
adenosine (
Ado), a molecule that is controlled by NTPDase,
5'-nucleotidase and
adenosine deaminase (ADA)
enzymes. Thus, the aim of this study was to investigate the involvement of purinergic
enzymes in the pathogenesis of A. hydrophila
infection, and whether the purinergic pathway and innate immune response are involved in the protective effects of TTO in
silver catfish (Rhamdia quelen) experimentally infected with A. hydrophila. Our results revealed that A. hydrophila
infection increased seric NTPDase and
5'-nucleotidase activity, while ADA activity decreased. Also, the seric levels of pro-inflammatory
cytokines such as
interleukin-1 (IL-1),
IL-6,
tumor necrosis factor alpha (TNF-α) and
interferon gamma (INF-γ) increased in the infected fish, while the seric level of anti-inflammatory
interleukin-10 (IL-10) decreased. Treatment with TTO was able to prevent the impairment of purinergic
enzymes and improve the innate immune response through the modulation of
cytokine response during A. hydrophila
infection. In summary, prophylactic
therapy with TTO can be considered an important approach to improve the immune response and consequently avoid the inflammatory process in fish infected with A. hydrophila.