Aims: To investigate effects of various concentrations of the essential oil of Cuminum cyminum L. seed alone and in combination with nisin on survival of vegetative forms of Bacillus cereus and Bacillus subtilis in a food model (commercial barley soup) and their ultrastructure. Methods and Results: Gas chromatography-mass spectrometry analysis indicated that cumin aldehyde (29 center dot 02%) and alpha-terpinen-7-al (20 center dot 70%) constituted the highest amount of the essential oil. The lowest concentration of the essential oil significantly affected the growth of the bacteria at 8 degrees C but not at 25 degrees C. Synergistic effect of the essential oil in combination with the lowest concentration of nisin was observed on the bacteria at 8 degrees C. Evaluation of the sensory properties showed that concentration of 0 center dot 15 mu l ml-1 of the essential oil was the most acceptable. Conclusions: The essential oil of C. cyminum L. seed showed the most bactericidal effects on B. cereus at 8 degrees C. Ultrastructural studies of vegetative cells confirmed the synergistic destructive effects of the essential oil and nisin on membrane and cell wall of the bacteria. Significance and Impact of the Study: Utilization of essential oil of C. cyminum L. seed in combination with nisin can inhibit growth of food-borne pathogens in food.