The antimicrobial effects of garlic, ginger, carrot and turmeric pastes against Escherichia coli O157:H7 in laboratory buffer and model food system were investigated. Turmeric paste, fresh carrot, ginger and garlic pastes from roots, and commercial ginger and garlic paste were heated alone or with buffered peptone water (BPW) or ground beef at 70 degrees C for 7 min. All samples were inoculated with a three strain cocktail of overnight cultures of E. coli O157: H7 and stored at 4 degrees C and 8 degrees C for 2 weeks. Each paste exhibited different antimicrobial effects alone and in ground beef or BPW at 4 degrees C and 8 degrees C for 2 weeks. Commercial ginger paste and fresh garlic paste showed the strongest antimicrobial activity with complete inactivation of E. coli O157:H7 in the paste at 3 days at 4 degrees C and 8 degrees C. Carrot and turmeric pastes did not show any antimicrobial activity both at 4 degrees C and 8 degrees C. Commercial garlic showed antimicrobial activity at both 4 degrees C and 8 degrees C (about 1 log CFU/g reduction) in the paste. However, fresh ginger paste showed antimicrobial activity only at 8 degrees C. Only commercial ginger paste had antimicrobial activity in BPW at 4 degrees C for 2 weeks. However, commercial ginger paste showed antimicrobial activity in ground beef at 3 days and after (about 1-2 log CFU/g) compared to control samples at 8 degrees C for 2 weeks. Fresh garlic paste showed antimicrobial activity only in BPW (1.3 log CFU/g) at 8 degrees C. These results indicate that the antimicrobial activity of these pastes is decreased in ground beef and laboratory buffer.