This work were aimed to (a) determination of minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) of Carum copticum essential oil (EO) against Escherichia. coli O157:H7 in vitro Trypticase Soy Broth, (TSB) and in ground beef; (b) evaluation of the effect of sub-inhibitory concentrations (sub-MICs) of EO on the growth of bacterium in TSB over 72 h (at 35 A degrees C) and ground beef over 9 days (at 4 A degrees C); and (c) investigation of gene expression involved in Shiga toxins production using relative quantitative real-time PCR method. The MIC in broth and ground beef medium were determined as 0.05 (v/v) and 1.75 % (v/w), respectively. In comparison with control cultures, the EO concentration of 0.03 % in broth caused reduction of colony counting as 1.93, 1.79, and 2.62 log(10) CFU ml(-1) after 24, 48, and 72 h at 35 A degrees C, and similarly EO (0.75 %) in ground beef resulted to reduction of colony counting as 1.03, 0.92, 1.48, and 2.12 log(10) CFU g (-1) after 2, 5, 7, and 9 days at 4 A degrees C, respectively. An increase and decrease in gene expression were observed as result of EO addition (0.03 %) to broth and (0.5 %) to ground beef was noticed, respectively.