Antimicrobial power of various nature-identical compounds against Vibrio spp.

One of the most important purposes in aquaculture is the control of disease outbreaks and, among them, Vibriosis is considered a significant problem for several aquatic species. The study of compounds with antimicrobial properties alternative to antibiotics, like phytogenics, is receiving a growing attention. The aim of this study was to screen the in vitro antimicrobial activity of 11 nature-identical compounds (NIC) against 2 Vibrio species, V. harveyi and V. anguillarum. The NIC tested were thymol (Thy), carvacrol (Car), vanillin (Van), eugenol (Eug), cinnamaldehyde (Cin), geraniol (Ger), a-pinene (Pin), eucalyptol (Euc), menthol (Men), linalool (Lin), and limonene (Lim). V. harveyi, isolated from farmed gilthead seabream, and V. anguillarum (ATCC 19264) were cultured at 25°C in tryptic soy broth (TSB) supplemented with 1.5% NaCl and used as inoculums. The antimicrobial activity was evaluated after 24h incubation with microdilution method in TSB in which the substances were dissolved at the following concentrations: 7,5, 3.75, 1.88, 0.94, 0.47, 0.23 and 0.12 mM. Control strains were incubated with TSB only. The analysis was performed on 96-wells microtiter plates with 10⁵ cfu/mL and the growth inhibition was evaluated by absorbance measurement at 620 nm after incubation. Thy and Car showed the lowest MIC against V. harveyi (0.94 mM) and, along with Eug, against V. anguillarum (1.88 mM). Cin inhibited the growth of V. harveyi at 1.88 mM and V. anguillarum at 3.75 mM. Eug, Van, and Ger were able to inhibit the growth of both Vibrio species at the respective concentrations of 1.88, 3.75, and 7.5 mM. Instead, Pin, Euc, Men, Lin and Lim were not effective even at the highest doses. All the results are reported in the graphs in Fig. 1. In conclusion, these findings showed the antimicrobial power of Thy, Car, Eug, Van, Cin, and Ger against 2 Vibrio spp., highlighting the interest of their use as feed additives in aquaculture.

Figure 1: Growth of V. anguillarum (A) and V. harveyi (B) when cultured with the different NIC

Acknowledgements: This research was funded by Vetagro S.p.A. and POR-FESR 2014-2020 Emilia Romagna grant.

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