Potencial antibacteriano dos óleos essenciais de Lippia sidoides, Ocimum gratissimum e Zingiber officinale frente Aeromonas hydrophila, patógeno de tambaqui (Colossoma macropomum)

Abstract

The objective of this work was to evaluate the antimicrobial activity of Lippia sidoides, Ocimum gratissimum and Zingiber officinale essential oils (EOs) in vitro and in vivo by therapeutic baths and the supplementation in the diet of tambaquis juveniles (Colossoma macropomum) and their effects on growth, hematological, biochemical and histological parameters after challenge with Aeromonas hydrophila. In chapter 1, in vitro tests were carried out against 10 strains of A. hydrophila isolated from tambaquis, in addition to determining their chemical composition. The main compounds present in EOs were thymol (76.6%), p-cymene (6.3%) and β-caryophyllene (5.0%) for L. sidoides, eugenol (43.3%), 1.8-cineole (28.2%) and β-selinene (5.5%) for O. gratissimum and geranial (23.2%), neral (16.7%) and 1,8-cineole (15.8%) to Z. officinale. All EOs evaluated showed bactericidal action against 10 strains of A. hydrophila, with minimal inhibitory concentration (MIC) and minimum bacterial concentration (MBC) ranging from 625 to 5,000 μg mL−1. Among the evaluated EOs, L. sidoides showed the best antimicrobial activity against A. hydrophila strains (MIC and MBC varing from 625 to 1,250 μg mL-1). In chapter 2, tambaqui juveniles were experimentally infected with A. hydrophila, and then subjected to 60-minute therapeutic baths for 5 consecutive days. The treatments applied were: 1) positive control (infected with A. hydrophila and no OE added), 2) negative control (infected with A. hydrophila and added 10 mg L-1 gentamicin), 3) 2.5 mg L-1 and 4) 5.0 mg L-1 of L. sidoides EO, 5) 5.0 mg L-1 and 6) 10.0 mg L-1 of O. gratissimum EO, 7) 5.0 mg L-1 and 8) 10.0 mg L-1 of Z. officinale EO, each with three repetitions, with fish survival recorded for 10 days. The highest survival rate of tambaqui was achieved by the group treated with 5.0 mg L-1 O. gratissimum (89.5%), values close to those obtained in the negative control group. Already with 5.0 mg L-1 of the L. sidoides EO the survival was 75.0%, and for the other treatments with EO the survival values were close to or below those registered for the positive control group (70.8%). In the evaluation of hematological and biochemical parameters it was observed reduction in hematocrit, hemoglobin and erythrocyte number in tambaqui exposed to L. sidoides and Z. officinale EO in control groups, however there was no significant change in plasma glucose, total protein values and the enzymes aminotransferases (aspartate and alanine aminotransferase) among the evaluated treatments. Histopathological analysis of liver tissue of tambaqui infected with A. hydrophila after baths with Eos showed mild to moderate damage. O. gratissimum and L. sidoides EOs, applied via baths, promoted better survival of tambaquis infected with A. hydrophila, however additional strategies are needed for the use of these essential oils as antibacterial. In chapter 3, the effect of the inclusion of L. sidoides, O. gratissimum and Z. officinale Eos in the diet of tambaquis juveniles on the growth, hematological and immunological parameters, as well as their resistance to infection induced by A. hydrophila was evaluated. Seven diets were prepared (32% crude protein) containing two concentrations of each essential oil evaluated, comprising the treatments: 1) 0 g kg-1 (control); 2) 0.625 g kg-1 and 3) 1.25 g kg-1 of L. sidoides EO; 4) 1.25 g kg-1 and 5) 5.0 g kg-1 of O. gratissimum EO; 6) 1.25 g kg-1 and 7) 5.0 g kg-1 of Z. officinale EO, with three repetitions. At the end of 30 and 60 days of feeding, the performance parameters and some hematological variables did not show significant differences between treatments (p <0.05), being observed only reduction of total thrombocytes at the end of 30 days of feeding with 1.25. g kg-1 and 5.0 g kg-1 of O. gratissimum EO. After 60 days, tambaqui juveniles were challenged with the bacteria A. hydrophila (1.6 x 108 CFU mL-1) and observed for 10 days. The addition of 0.625 and 1.25 g kg-1 of L. sidoides EO in tambaqui diet promoted nonspecific immunity responses through increased leukocyte respiratory activity after induced infection, with a reduction in plasma glucose levels, which suggests insulin action, and no change in total protein levels. The survival of A. hydrophila-infected fish was higher in those fed with 0.625 g kg-1 of L. sidoides EO.