Comparing the antimicrobial effectiveness of genistein and daidzein on some food-borne pathogen bacteries

The isoflavones genistein and daidzein are phytoestrogens which are found at high levels in soy products. These isoflavones are currently of growing interest owing to their beneficial effects on many disorders, including cancer, cardiovascular diseases and osteoporosis. However, there is little information on the antimicrobial effects of these isoflavones. The purpose of the present study was to compare the antimicrobial effects of genistein and daidzein against seven important foodborne pathogens, namely E. coli O157:H7, Listeria monocytogenes, Bacillus cereus, Staphylococcus aureus, Vibrio parahaemolyticus, Salmonella typhimurium, and Cronobacter sakazaki. To achieve this purpose, the effect of different concentrations of genistein or daidzein on the lag phase duration of growing bacteria was evaluated by measuring the optical density of the samples during 24 h at 35 ºC. According to the results of the present study, the lag phase duration of E. coli O157:H7 was not altered significantly in the presence of up to 1000 µM of both the isoflavones (p>0.05). However a significant increase in the lag phase duration of B. cereus, S. aureus and S. typhimurium was observed in the presence of 500 µM of genistein or 1000 µM of daidzein (p<0.05). Furthermore, both isoflavones made a significant increase in the lag phase duration of L. monocytogenes and V. parahaemolyticus in the concentration of 125 µM and also in the lag phase duration of C. sakazakii in the concentration of 1000 µM (p<0.05). In conclusion, in the presence of 1000 µM of genistein and daidzein, the lag phase duration of all the tested bacteria were significantly increased except for E. coli O157:H7.