The survival and hepatic and muscle glucose and lactate levels of Rhamdia quelen inoculated with Aeromonas hydrophila and treated with terpinen-4-ol, carvacrol or thymol.

The aim of this study was to evaluate the resistance of Rhamdia quelen (silver catfish) to Aeromonas hydrophila infection after treatment with pure and nanoencapsulated forms either terpinen-4-ol, thymol, or carvacrol and the effects of these treatments on fish metabolic responses. After A. hydrophila inoculation, fish were treated with 30 min daily baths for 6 consecutive days with terpinen-4-ol, thymol, or carvacrol in their pure or nanoencapsulated forms at concentrations of 5, 10, 15 or 25 mg L-1. A positive control group, negative control group and saline group were also included. Survival was evaluated at the end of treatment for six consecutive days. Muscle and liver were collected to determine glucose and lactate levels. The fish treated with the nanoencapsulated form of the compounds had a high survival rate, similar to saline group and negative control groups. The carvacrol, thymol and terpinen-4-ol nanoencapsulated forms improved survival of silver catfish infected with A. hydrophila. Muscle and liver glucose and lactate levels are not indicated as biomarkers because they did not present any correlation between the metabolic state of the fish and the bacterial infection.

The antibacterial and physiological effects of pure and nanoencapsulated Origanum majorana essential oil on fish infected with Aeromonas hydrophila.

This study evaluated the antibacterial activity of Origanum majorana essential oil (EOM) and nanocapsules of this oil (NOM) in silver catfish, Rhamdia quelen, infected with Aeromonas hydrophila, and addressed their effects on silver catfish hematological and metabolic parameters. Fish were inoculated with A. hydrophila (360 µL, at a concentration of 1.5 × 109 CFU mL-1) and submitted to 1 h daily baths with EOM (0 (control), 20 or 30 µL L-1), NOM (0 (control), 5 or 10 µL L-1) or a positive control containing florfenicol (30 µL L-1) called group Maxflor® for five consecutive days. All treatments improved the survival rate of the infected fish, but we suggest the treatment of A. hydrophila infections through daily baths with 20 µL L-1 EOM or 5 µL L-1 NOM for five consecutive days as these were the lowest effective concentrations tested. Silver catfish treated with EOM and NOM had higher lymphocyte levels, indicating stimulation of the immune system in these fish. The lowest liver glucose level was found in the group treated with the lowest concentration of NOM, and the lactate values in the liver and muscle of all groups were within the normal values reported for this species. In addition, nanocapsules required much less EOM to elicit effective antibacterial treatment.

Ecotoxicology of Glycerol Monolaurate nanocapsules.

Glycerol Monolaurate (GML) is a compound with known antimicrobial potential, however it is not much used due to its low solubility in water and high melting point. The nanoencapsulation of some drugs offers several advantages such as improved stability and solubility in water. The present study aimed to produce, characterize, and evaluate the ecotoxicity of GML nanocapsules. The nanocapsules were produced and presented a mean diameter of 210nm, polydispersity index of 0.044, and zeta potential of -23.4mV. The electron microscopy images showed the nanometric size and spherical shape. The assay in soil showed that GML has a high toxicity while the GML nanocapsules showed decreased toxic effects. Nanostructuration also protected the Rhamdia quelen against the toxic effects of GML. Concluding, the formulation shows positive results and is useful to predict the success of development besides not damaging the soil.