Dietary supplementation with caffeine increases survival rate, reduces microbial load and protects the liver against Aeromonas hydrophila-induced hepatic damage in the grass carp Ctenopharyngodon idella

The indiscriminate use of antibiotics is a major concern for the aquaculture industry because of the increasing prevalence of bacterial resistance, including the emergence of multi-resistant strains of Aeromonas hydrophila. Therefore, alternative ecofriendly therapeutic or prophylactic approaches such as natural products have been suggested, including caffeine, a methylxanthine with potent bactericidal and antioxidant properties. The aims of this study were to evaluate whether dietary supplementation with caffeine exerted bactericidal effects against A. hydrophila, and to determine whether caffeine protected the liver of grass carp (Ctenopharyngodon idella) against A. hydrophila-induced oxidative damage. Experiment I evaluated the antimicrobial properties of caffeine dietary supplementation linked to longevity and mortality rates during aeromonosis. Fish infected with A. hydrophila that were fed diets containing 5% and 8% caffeine lived significantly longer than those fed with control diets. Experiment II evaluated hepatic oxidative stress-related parameters and microbial loads on day 7 post-infection. Levels of hepatic reactive oxygen species (ROS), lipid peroxidation (LOOH) and protein carbonylation (PC) levels were significantly higher in infected fish fed with control diet than in uninfected fish, and hepatic antioxidant capacity against peroxyl radicals (ACAP) levels, and superoxide dismutase (SOD), glutathione peroxidase (GPx), glutathione S-transferase (GST) and glutathione reductase (GR) activities were significantly inhibited. Dietary supplementation with 5% and 8% caffeine prevented the increase on hepatic ROS, LOOH and PC levels (except 5% caffeine) elicited by infection. Caffeine supplementation reduced or prevented the inhibition of hepatic SOD, GPx and GST activities. Finally, both caffeine concentrations reduced the hepatic microbial load compared to fish fed with control diets that were infected with A. hydrophila. Taken together, the data suggest that dietary supplementation with 8% caffeine may be considered a compelling prophylactic approach to aeromonosis caused by A. hydrophila.