3.2. Inhibitory activity
The inhibitory activity of reuterin, determined using E. coli K12 as indicator strain, was estimated to be 510 AU/ml. The antimicrobial effect of reuterin on L. monocytogenes growth was determined by measuring the optical density. Survival curves of the three strains studied in double strength TSB with reuterin at different concentrations are shown in Fig. 1. Estimated maximum growth rates and lag time by using DMFit Excel add-in software are shown in Table 1. For the three strains, maximum growth rates were significantly reduced (P < 0.001) and lag times increased (P < 0.001) by reuterin. According to the data obtained in the microplate reader, the concentration required to inhibit the growth of L. monocytogenes strains INIA 2530, INIA H66a and CECT 5725 during 24 h at 37 C was 4, 4, and 2 AU/ml, respectively.