Linalool, citral, eugenol and thymol: control of planktonic and sessile cells of Shigella flexneri

The antimicrobial activity of linalool, citral, eugenol and thymol was determined in growth studies of both planktonic (PC) and biofilm cells (BC) Shigella flexneri. These components were evaluated either in isolation or in combinations using a sequential experimental strategy with Plackett & Burman and central composite rotational designs totaling 47 treatments. The minimum inhibitory concentration for PC was 0.125% (v v^-1) for linalool and 0.5% (v v^-1) for citral, eugenol and thymol. The biofilm minimum bactericidal concentration was 3 and 1% (v v^-1) for linalool and citral, respectively, and 2% (v v^-1) for eugenol and thymol. In the mixtures, the minimum concentrations in the efficient assays for PC growth inhibition were 0.0003, 0.0443 and 0.0443% (v v^-1), for linalool, citral and thymol, respectively. In the BC, only two assays with concentrations of 0.0558, 0.0558 and 0.319% (v v^-1) and 0.035, 0.035 and 0.3999% (v v^-1) for linalool, citral and thymol, respectively, inhibited Shigella growth. Synergism was observed among the components, where PC and BC growth inhibition occurred at lower concentrations than those noted individually. The bactericidal effect of the components in microplate was different from the observed in stain steel coupons. Therefore, the obtained model can describe and predict the PC count of S. flexneri in medium with the tested compounds and they could be an alternative for the use in microbiological control in food industry.