Plant Essential Oils Inhibit Growth and Histamine Production of Aeromonas hydrophila Isolated from Skipjack Tuna

The accumulation of histamine in fish products represents a significant food safety issue, particularly in skipjack tuna (Katsuwonus pelamis), due to its elevated histidine content. This study sought to isolate histamine-producing bacteria from skipjack tuna and assess the inhibitory effects of six plant-derived essential oils on bacterial proliferation and histamine synthesis. Seven bacterial isolates were obtained and screened, with histamine concentrations quantified via high-performance liquid chromatography (HPLC) following dansyl chloride derivatization. The isolate exhibiting the highest histamine production (1.2 ± 0.2 mM) was identified as Aeromonas hydrophila through 16S rDNA sequencing. Essential oils were administered to bacterial cultures prior to histamine quantification, and their minimum inhibitory concentrations (MICs) and minimum bactericidal concentrations (MBCs) were determined in vitro. Among the tested oils, oregano and cinnamon demonstrated the strongest antibacterial activity, with MIC and MBC values below 1 mg/mL. Scanning electron microscopy analysis revealed pronounced structural damage to bacterial cells treated with these oils. At the MBC, histamine production was entirely suppressed; at half the MBC, histamine synthesis was reduced by more than 90%, whereas lower concentrations yielded moderate inhibition ranging from 15% to 22%. These findings suggest that selected essential oils, notably oregano and cinnamon, possess considerable potential as natural preservatives to reduce histamine formation in skipjack tuna. However, further investigation is necessary to confirm their effectiveness under practical storage conditions.