Purpose: The aim of this work was to determine the antimicrobial effect of Mexican oregano EO in combination with olive oil, simulating fat content in food against food contamination bacteria.
Methods: Microorganisms used were Bacillus cereus, Escherichia coli, E. coli 0157: H7, Listeria monocytogenes, Salmonella Typhimurium and Staphylococcus aureus. A Checkerboard Method in glass test tubes with 2000 µl of TSB were used, with the following concentrations of the factors studied: olive oil (control, 1-7%); Mexican OEO (50, 100, 200, 300, 400,500, 600, 700, 800, 900 mg/l). Tubes were inoculated with the bacterial strains and incubated for 24 hours at 37° C. After incubation, 200 µl of each tube were transferred to the microplate and revealed with 50 µl of 0.1% resazurin. Fractional inhibitory concentrations (FIC= FICA + FICB) were calculated to demonstrate synergism, antagonisms or indifference.
Results: An antagonism is shown for the Bacillus cereus, Listeria monocytogenes and S. aureus strains since the obtained numerical value were 5.1428, 7.7142 and 6.2857, respectively. While for strains E. coli, E. coli O157: H7 and Salmonella Typhimurium results are 2.1428, 2.6428 and 3.1428, respectively, and showed an indifferent effect.
Significance: Results demonstrate that the antimicrobial effect of oregano can be influenced by the composition of the food where the antimicrobial is added, and should be considered as a problem when natural antimicrobials are considered for hurdle technology.