2.3. Antimicrobial activity assay

Individual colonies of E. coli O157:H7 F4546 and K4492 were inoculated in tryptic soy broth (TSB; Becton Dickinson, Sparks, MD USA) and incubated at 37 °C for 16–18 h. The bacterial cultures were serially diluted in TSB to ca. 5 Log CFU/ml. Each of the ten extracts described above was added to a test tube with the diluted bacterial suspension, at a concentration of 9% or 23% (v/v). The control groups did not contain any extract, and sterilized distilled water was used to make up the missing volumes. The susceptibility of E. coli O157:H7 F4546 and K4492 to different concentrations of the extracts was determined using the plate count assay. After 5, 10, and 24 h of incubation at room temperature on an orbital platform shaker (Model: 3520, Lab-line, IL USA), an aliquot of each sample was serially diluted and spread plated onto tryptic soy agar (BD Diagnostic Systems) plates in duplicate. The inoculated plates were then incubated at 37 °C for 16–18 h. The inhibitory effect of the extracts was expressed as E. coli cell population reduction in the experimental groups compared to the population in the control groups. All experiments were reproduced twice.