Synergistic effect of Nisin and Cuminum cyminum L. essential oil on the growth of Streptococcus iniae in fillets of rainbow trout (Oncorhynchus mykiss)

Streptococcus iniae is an emerging zoonotic pathogen that represents a threat to the aquaculture industry worldwide and poses a risk to humans’ health. The aim this study, was to evaluate the effect of cumin (Cuminum cyminum) essential oil and nisin on the growth of S. iniae. For this purpose, the fillets of rainbow trout (Oncorhynchus mykiss) were inoculated with 103 of S. iniae and afterwards were treated with the different concentrations of cumin essential oil (0, 0.005, 0.135 and 0.405%) as well as nisin (0, 0.25 and 0.75 μg/ml). The samples were stored at 4 and 10 ºC for 15 days. Results revealed that in the samples stored at 4 °C the solo application of each of nisin and cumin essential oil could inhibit the growth of S. iniae until day 9; meanwhile, in combining form the inhibition of bacterial growth was occurred for 3 days. In the samples stored at 10 ºC, nisin and cumin essential oil hindered the bacterial growth for 3 and 6 days, respectively. Moreover, combination of the two materials inhibited the bacterial growth until day 6. The highest synergistic effect was observed in 0.405% of cumin essential oil and 0.75 μg/ml of nisin at 4 ºC. However, at 10 ºC, 0.135 and 0.405% of cumin essential oil together with 0.75 μg/ml of nisin had the highest synergistic effect. As a significant (P<0.05) difference was observed between the treatment and control groups, it could be concluded that cumin essential oil and nisin could efficiently inhibit the growth of S. iniae.