Prophylatic potential of essential oils against Aeromonas spp. in Colossoma macropomum

Abstract

The aim of this study was to identify and evaluate the pathogenic potential of Aeromonas species associated with semi-intensive farming systems of tambaqui (Colossoma macropomum) in the state of Amazonas, Brazil, as well as to investigate the antimicrobial activity of nine essential oils (Croton sacaquinha, Cymbopogon nardus, Curcuma longa, Lippia origanoides, Mentha arvensis, Ocimum basilicum, Ocimum micranthum, Piper hispidum e Piper marginatum) and their prophylactic potential against Aeromonas hydrophila infection. Chapter 1 consisted of a literature review addressing the status of aquaculture and tambaqui farming, the occurrence of aeromoniasis in aquaculture, the use of antimicrobials and essential oils in the cultivation of aquatic organisms, and the application of essential oils in tambaqui farming. Chapter 2 aimed to isolate and characterize Aeromonas strains from farmed tambaqui through bacterial isolation, molecular identification, and assessment of their pathogenic potential based on the presence of virulence genes and in vivo pathogenicity assays. Five strains of A. hydrophila and one strain of A. jandaei were isolated. The Aeromonas strains tested positive for at least seven virulence factors. Fish subjected to the lethal dose (LD) determination assay exhibited skin depigmentation, ulcerations, lethargy, and hypo/anorexia in all inoculated groups, whereas fish in the control group showed no clinical signs. The LD10, LD50, LD90, and LD99 values were established at 9.1 × 10⁶, 2.9 × 10⁷, 9.1 × 10⁷, and 2.3 × 10⁸ CFU mL⁻¹, respectively. Chapter 3 aimed to determine the chemical composition and antimicrobial activity of nine essential oils (EOs) against strains of A. jandaei and A. hydrophila isolated from tambaqui. The major compounds identified in the EOs of C. sacaquinha, C. nardus, C. longa, L. origanoides, M. arvensis, O. basilicum, O. micranthum, P. hispidum, and P. marginatum were β-selinene (14.5%), geraniol (53.3%), ar-turmerone (30.2%), carvacrol (43.3%), menthol (88.5%), methyl chavicol (33.9%), piperitone oxide (36.2%), γ-terpinene (37.1%), and δ-3-carene (13.1%), respectively. The EOs of L. origanoides (9.2 mg mL⁻¹), C. nardus (10 mg mL⁻¹), M. arvensis, and P. marginatum (15 mg mL⁻¹) exhibited the most pronounced antimicrobial activity, whereas all tested EOs demonstrated bactericidal activity against Aeromonas strains. Chapter 4 aimed to evaluate the effects of dietary supplementation with the essential oils of C. nardus, L. origanoides, and M. arvensis on growth performance, hematological and immunological parameters, and the survival of tambaqui following challenge with A. hydrophila. Dietary supplementation with essential oils promoted distinct responses in juvenile tambaqui, improving growth performance, feed efficiency, and resistance to A. hydrophila infection. C. nardus was the most effective in enhancing final weight and feed conversion ratio, whereas L. origanoides and M. arvensis provided the highest survival rates following the bacterial challenge, without compromising the hematological and biochemical homeostasis of the fish.