In vitro activity of some essential oils alone and in combination against the fish pathogen Nocardia seriolae

Abstract

Microplate resazurin assay was applied to investigate the in vitro activity of four essential oils (EOs); cinnamon (Cinnamomum zeylanicum), thyme (Thymus vulgaris), lemongrass (Cymbopogon flexuosus) and tea tree (Melaleuca alternifolia) oils against 80 clinical isolates of the fish pathogen Nocardia seriolae. The checkerboard test was then used to determine the possible synergistic effect of EOs combination against reference type strains of fish nocardiosis. All tested EOs had antibacterial activity against N. seriolae isolates. Among the tested EOs, cinnamon and thyme oils both exhibited the lowest minimum inhibitory concentrations (MICs) with 5-160 and 10-160 μg/ml, respectively. The activities of lemongrass and tea tree EOs were noted to be less effective with MICs of 20-640 and 160->5120 μg/ml, respectively. The checkerboard panel of cinnamon-thyme EOs combination against N. seriolae ATCC43993 demonstrated a synergistic effect with a fractional inhibitory concentration (FIC) index of 0.75. For N. salmonicida ATCC27463, the combination panel showed an additive effect with an FIC index of 1.0. For N. asteroides ATCC19247, the combination panel demonstrated an indifference effect with an FIC index of 1.125. These results indicate that thyme and cinnamon oils alone or the combination of them at a given ratio has a promising potent clinical significance in the treatment of fish nocardiosis. Despite the promising results given by our in vitro studies, the clinical benefits of these EOs combinations can only be determined through carefully designed in vivo experimental studies.

Antiparasitic and Antibacterial Functionality of Essential Oils: An Alternative Approach for Sustainable Aquaculture

“…Nocardia seriolae is the causative agent of nocardiosis in cultured fish species [115]. Ismail and Yoshida [116] reported that MIC values of C. Zeylanicum, Thymus vulgaris, Cymbopogon flexuosus, and Melaleuca alternifolia EOs on 80 Nocardia seriolae isolates were in the range of 5 to >5120 µg/mL, and the most effective herb species were C. zeylanicum and T. vulgaris with MICs 5-160 µg/mL, respectively.…”

Chemical composition, cytotoxicity and antimicrobial activity of selected plant‐derived essential oils against fish pathogens

“…Some EOs and some major components of EOs identified in this study have already been reported to possess potent antimicrobial activity, either alone or in combination with other antimicrobials, against different bacteria (Alizadeh Behbahani & Imani Fooladi, 2018; Chouhan et al., 2017; Malik et al., 2019; Tariq et al., 2019; Thielmann et al., 2019), including strains isolated from fish (Ismail & Yoshida, 2017). However, based on interpretative criteria proposed by Aligiannis et al.…”

Pathogenicity, diagnosis, prevention strategies and immune response of bacterium Nocardia seriolae : A critical review

“…These genome databases have revealed new information on N. seriolae epidemiology, pathogenesis, transmission and infection control techniques. Traditionally, the pharmaceutical therapy to overcome fish nocardiosis involves several antibiotics, such as sulfamonomehizol and sulfisizole, which have already been approved in Japan as effective treatments for N. serioale infections (Ismail et al, 2012; Ismail & Yoshida, 2017). However, this effort displayed only partial effectiveness with severe problems of microbial resistance, drug residues and environmental pollution (Ismail & Yoshida, 2017).…”

“…Traditionally, the pharmaceutical therapy to overcome fish nocardiosis involves several antibiotics, such as sulfamonomehizol and sulfisizole, which have already been approved in Japan as effective treatments for N. serioale infections (Ismail et al, 2012; Ismail & Yoshida, 2017). However, this effort displayed only partial effectiveness with severe problems of microbial resistance, drug residues and environmental pollution (Ismail & Yoshida, 2017). By contrast, vaccination is a more effective strategy to overcome the epidemics of nocardiosis through activating the fish immune system with many advantages in long‐term efficacy protection and environmental friendliness.…”