In Vitro Antibacterial Potential of Plant Extracts and in Vivo Ilex paraguariensis Effect on Oreochromis niloticus Physiology and Resistance to Aeromonas hydrophila

The aim of the study was to investigate the antibacterial potential of garlic (Allium sativum), pinus (Pinus elliottii), eucalyptus (Eucalyptus sp.), yerba mate (Ilex paraguariensis) and guava tree (Psidium guajava Linn.) in vitro and the effect of yerba mate supplementation on Oreochromis niloticus physiology and resistance to Aeromonas hydrophila. The in vitro antibacterial potential of the plants was verified by the minimum inhibitory concentration (MIC) method and by the antimicrobial sensitivity test (TSA). The in vivo assay was performed using diet supplementation with yerba mate and challenge with A. hydrophila. After the supplementation and challenge periods biochemical, immune and physiological parameters were evaluated. The in vitro assays showed that only yerba mate presented antibacterial potential against A. hydrophila and no one of the plant extracts were effective against Streptococcus agalactiae. The use of yerba mate in the diet did not influence the immune and metabolic status of O. niloticus. Also, the supplementation did not act as a growth promoter for the fishes. Considering the challenge of O. niloticus with A. hydrophila, the yerba mate did not improve the resistance of the fishes to the bacteria. The yerba mate extract presented potential to be used as an antibacterial agent for fish diseases. Also, more detailed studies are necessary to stablish effective doses and times required for fish treatments.