Effects of exposure to biocides on susceptibility to essential oils and chemical preservatives in bacteria from organic foods

A collection of 38 biocide-adapted strains with significant increases in their tolerance to biocides after step-wise exposure to these compounds were screened for sensitivity to essential oils and chemical preservatives. Several strains adapted to quaternary ammonium compounds (benzalkonium chloride, hexadecylpyridinium chloride or cetrimide) showed a generalized increase in the sensitivity to preservatives. Similar results were found among hexachlorophene- or chlorhexidine-adapted strains. Moreover, tolerance to hexadecylpyridinium chloride showed a very strong positive correlation with 4-hydroxybenzoic acid, thyme oil and sodium nitrite increased sensitivity, as well as a strong correlation with clove oil, potassium sorbate and potassium nitrate increased sensitivity. On the contrary, an increase In tolerance to preservatives was detected among triclosan-adapted strains. Results from this study suggest that exposure of bacteria from foods to biocides is not always associated with co-selection for other antimicrobial resistances, especially against essential oils or chemical preservatives used in the food industry. (C) 2017 Elsevier Ltd. All rights reserved.