Growth response of Escherichia coli ATCC 35218 adapted to several concentrations of sodium benzoate and potassium sorbate.

Escherichia coli ATCC 35218 growth response was evaluated after repetitive cultivation in stepwise increasing antimicrobial agent concentrations (potassium sorbate or sodium benzoate) to observe its adaptation process to high weak-acid concentrations. The effect of antimicrobial (potassium sorbate or sodium benzoate) concentration (0 to 7,000 ppm) was tested using laboratory media. Cells adapted at 1,000 ppm were inoculated in media containing the same concentration of the antimicrobial; after that, cells were transferred to media containing a higher concentration, followed by repetitive cultivations. In every case, viable cells were determined by surface plating every hour up to 48 h. Logarithmic representations of survival or growing fraction were modeled using the Gompertz equation. Adapted and nonadapted cells were analyzed for plasmid presence as well as phosphofructokinase and succinate dehydrogenase activity. Bacterial growth was observed after adaptation processes in media formulated up to 7,000 ppm of potassium sorbate or sodium benzoate. Analyses of variance demonstrated that no significant difference (P > 0.05) in lag time or growth rate was observed among adapted cells cultured in media containing the studied concentrations for each of the antimicrobials tested. These results suggest that E. coli can be adapted to high weak-acid concentrations if the exposure is performed under sublethal conditions. Furthermore, there was demonstrated inhibition of the enzymes phosphofructokinase and succinate dehydrogenase by action of sodium benzoate and potassium sorbate, respectively. E. coli adaptation to antimicrobial agents was not related to plasmid presence but appears to be due to other action mechanisms.