The antimicrobial effect of Origanum compactum essential oil, nisin and their combination against Escherichia coli in tryptic soy broth (TSB) and in sheep natural sausage casings during storage at 25 and 7°C

Abstract

The aim of this study was to investigate the antimicrobial effect of oregano essential oil (EO) at 0.015, 0.03 or 0.06%, nisin at 800 or 1600 IU/g, and their combination on Escherichia coli in tryptic soy broth (TSB) and in sheep natural sausage casings. At 0.015%, EO presented a weak antibacterial activity against the pathogen in TSB. Consequently, only the levels of 0.03 and 0.06% were examined in casings. EO at 0.03 or 0.06% showed an inhibitory activity against E. coli O157:H7, E. coli ATCC 25922 and E. coli cocktail during storage at 25°C and at 7° C in casings. Treatment of casings or in TSB with nisin at 800 or 1600 IU/g did not show any antibacterial activity against E. coli strains. Synergy between EO and nisin was observed in both TSB and natural casings. The combination of EO at 0.03 or 0.06% and nisin at 800 or 1600 IU/g presented an additive effect against the pathogen, during storage at 25°C and at 7°C.

Key words: Oregano essential oil, nisin, natural casings, biopreservative, Escherichia coli