Antibacterial and antibiofilm activities and synergism with florfenicol from the essential oils of Lippia sidoides and Cymbopogon citratus against Aeromonas hydrophila.

AIMS: Aeromonas hydrophila is an opportunistic bacterium, with a high capacity for biofilm production, which can cause severe damage in aquaculture. The objective of this study was to identify the chemical compounds of the essential oils of Lippia sidoides (EOLS) and Cymbopogon citratus (EOCC), and to evaluate the biocidal, antibiofilm and synergistic action with the antimicrobial florfenicol of these essential oils (EOs) against A. hydrophila. METHODS AND RESULTS: The antibacterial activity of EOLS and EOCC was verified by the minimum bactericidal concentration and by the action of these EOs against both forming and consolidated biofilms. The synergistic activity of EOs with florfenicol was performed using the checkerboard technique. The main component of EOLS and EOCC was carvacrol (44.50%) and α-citral (73.56%), respectively. Both EOs showed weak inhibitory activity (≥3125.00 µg ml-1 ). Two bacterial isolates were able to produce biofilm, and EOLS and EOCC acted upon the bacterial isolates to prevent biofilm formation. A bactericidal effect was verified for EOLS in the previously consolidated biofilm for both isolates and for EOCC in only one of the isolates. In general, EOLS had a synergistic effect with florfenicol, while EOCF had an additive effect. CONCLUSIONS: Both EOs were able to interfere with biofilm formation and did not have an antagonistic effect in combination with florfenicol. The best results were found for EOLS, which showed a synergistic effect with florfenicol and the ability to interfere in the formation of consolidated biofilm. SIGNIFICANCE AND IMPACT OF THE STUDY: This study highlights the potential of EOLS and EOCC to interfere in biofilm and act in synergy with florfenicol to reduce the occurrence of A. hydrophila. Development of these compounds may contribute to the development of herbal medicines in aquaculture.

Glucose tolerance in six fish species reared in Brazil: Differences between carnivorous and omnivorous.

The objective of this study was to evaluate the effect of pure glucose, glucose plus fructose, and fructose on the blood glucose of omnivorous fish tambaqui (Colossoma macropomum), Nile tilapia (Oreochromis niloticus), piau (Leporinus elongatus), and carnivorous fish hybrid Amazon catfish (Pseudoplatystoma fasciatum × Leiarius marmoratus), pacamã (Lophiosilurus alexandri), and traíra (Hoplias malabaricus). In each species, the dose 1 mL per fish with 1,000 mg kg of body weight-1 of glucose, fructose or glucose plus fructose were tested intraperitoneally. Blood glucose was measured at times 0 (control), 0.5, 1, 2, 4, 8, 16, and 24 h. The administration of 1,000 mg of glucose or glucose plus fructose per kg of live weight causes hyperglycemia in the omnivorous and carnivorous species studied. In the omnivorous species, glycemic levels were reduced from 2 to 4 h, and the regulation to baseline occurred from 4 to 8 h. In the carnivores fish, blood glucose levels declined between 1 and 8 h, and return to baseline was observed from 8 to 16 h. Tambaqui was also intolerant to high concentrations of fructose. Blood glucose levels are regulated in a shorter time in Nile tilapia (mainly), piau and pacamã.

Cymbopogon flexuosus essential oil as an additive improves growth, biochemical and physiological responses and survival against Aeromonas hydrophila infection in Nile tilapia.

The objective of the present study was to evaluate growth, biochemical, hematological and intestinal enzymes responses and survival of Nile tilapia juveniles fed a diet containing the essential oil of lemongrass Cymbopogum flexuosus (EOCF) and infected by Aeromonas hydrophila. Five diets were evaluated (in quadruplicate) with increasing levels of EOCF (0.0 - control; 0.25; 0.50; 1.0 and 2.0 mL kg diet-1). On day 45, eight fish per treatment were sampled and blood, liver and intestine samples were taken. Others eight fish per treatment were infected with A. hydrophila followed by a 15-day period of observation. Citral is the main constituent of EOCF. The inclusion of 2.0 mL EOCF kg diet-1 increased specific growth rate and survival after A. hydrophila infection and decreased feed conversion ratio of Nile tilapia. In general, higher concentrations of EOCF in the diet reduced plasma glucose and triglycerides levels, and increased plasma amino acids, alanine aminotransferase (ALT) and hepatic ALT levels, hematological parameters, and the activity of intestinal enzymes. It was concluded that the inclusion of 2.0 mL EOCF kg diet-1 improved growth performance, biochemical and physiological responses and decreased mortality of Nile tilapia after A. hydrophila infection.