Effect of Rosmarinus officinalis Essential Oil and Nisin on Streptococcus iniae and Lactococcus garvieae in a Food Model System

The effects of concentrations of Rosmarinus officinalis essential oil (EO) and nisin (N) as well as temperature and storage time on growth of Streptococcus iniae and Lactococcus garvieae in Oncorhynchus mykiss were evaluated. According to analysis of the rosemary EO, the 1, 8-cineol and α-pinene were the predominant components. The growth of S. iniae was significantly decrease by EO concentrations at 4 ºC. For L. garvieae, the viable count was significantly inhibited by EO and N singly and in combinations, incubated at bath storage of 0.25 and 0.5 µg/mL proved insufficient to act against S. iniae and L. garvieae. The combinations of the rosemary EO at 0.0015% with N at 0.5 µg/mL showed stronger antimicrobial effect against two bacterial than the rosemary EO at 0% but lower than the combination with N at 0.5 µg/mL and EO at 0.045% which in turn was lower than of the rosemary EO at 0.135%. In its turn, rosemary EO showed lower antimicrobial activity than its combinations with N, which showed a bactericidal effect against the pathogens. The best inhibitory effects of EO in combinations with N for two bacterial were obtained at combinations of EO=0.135% and N=0.5 µg/mL.