Abstract
Antimicrobial activities of phytochemicals—trans-cinnamaldehyde (TC), ferulic acid (FA), p-coumaric acid (p-CA), caffeic acid (CA), chlorogenic acid (CHA), Thymus vulgaris essential oil (TO), Eugenia caryophyllus essential oil (ECO), and Melaleuca alternifolia oil (TTO) against Aeromonas species—were assessed. Growth of all Aeromonas salmonicida subsp. salmonicida and almost all Aeromonas sobria strains was inhibited by TC at concentration 0.01 mg/mL, and for most Aeromonas hydrophila strains minimal inhibitory concentrations (MIC) ranged from 0.01 to 0.19 mg/mL. The inhibitory effect of TC against A. salmonicida subsp. salmonicida was comparable to the effect of oxytetracycline, and in the case of A. salmonicida subsp. salmonicida and A. sobria was higher compared to gentamicin. MIC of FA, p-CA, and CA for most strains ranged from 1.56 to 3.12 mg/mL, and MIC values of TO for most strains ranged from 0.39 to 0.78 mg/mL. TO and TC at the concentrations below ½ MIC values used in mixtures exhibited strong synergism. ECO and TC showed synergy in mixture of ⅛ MIC of ECO and ¼ MIC of TC. TC and TO exhibited the strongest inhibitory and bactericidal effect against investigated Aeromonas species, and they are a promising alternative to the use of antibiotics in controlling the growth of these fish pathogens.
Highlights
Species belonging to the genus Aeromonas are ubiquitous and cosmopolitan gram-negative opportunistic bacteria commonly present in fresh water and often cause ulcer disease or hemorrhagic septicemia in fish [1,2]
Trans-cinnamaldehyde (TC) showed the highest antibacterial activity with the lowest minimal inhibitory concentrations (MIC) values ranging from 0.01 mg/mL to 0.19 mg/mL in case of the most A. hydrophila strains
The present study demonstrates the antibacterial activity of selected phytochemicals and indicates that they are a promising alternative to the use of antibiotics in controlling the growth of fish pathogens such as A. hydrophila, A. salmonicida subsp. salmonicida and A. sobria
Summary
Species belonging to the genus Aeromonas are ubiquitous and cosmopolitan gram-negative opportunistic bacteria commonly present in fresh water and often cause ulcer disease or hemorrhagic septicemia in fish [1,2]. Different species of Aeromonas cause severe skin lesions and anemia in fish resulting in high mortality [3,4]. According to Rasmussen-Ivey et al [5], virulence in Aeromonas hydrophila is multifactorial, including production and/or secretion of adhesins, cytotoxins, hemolysins, lipases, and proteases accompanied by the ability of biofilm formation. It is dangerous under intensive aquaculture conditions since stress caused by high stocking density and fishery management may suppress fish immune mechanisms and increase a risk of disease outbreak and accelerate disease transmission. Outbreaks of A. hydrophila infections are related to increased susceptibility of fish caused by adverse environmental conditions, such as hypoxia or nitrogenous waste buildup [5].
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