Adaptation and cross-adaptation of Escherichia coli ATCC 12806 to several food-grade biocides

Abstract

The objective of this paper was to determine whether Escherichia coli ATCC 12806 can adapt to growth in increasing concentrations of three biocides commonly used in food processing facilities (trisodium phosphate [TSP], sodium nitrite [SNI] or sodium hypochlorite [SHY]), and whether cross-adaptation occurs. Adaptability over time was estimated by the growth kinetic parameters (modified Gompertz equation): lag phase, maximum growth rate and cell density in the stationary phase. Attempts were made to determine whether efflux pumps (in the presence of the efflux inhibitor carbonyl cyanide m-chorophenyl hydrazone [CCCP]) and cell surface hydrophobicity changes (microbial adhesion to solvents [MATS] assay) are associated with this adaptation. After repeated sub-culturing in static broth cultures containing increasing sub-inhibitory concentrations of TSP, SNI or SHY, E. coli exhibited an adaptive tolerance, especially to SNI and SHY. The increased tolerance was stable and remained after 7 successive passages in biocide-free growth media. Cross-adaptation between dissimilar biocides (SNI and SHY) was observed. Both efflux pumps and changes in cell surface hydrophobicity appear to be associated with adaptation to SNI and SHY. It is suggested that sub-lethal exposure to food-grade biocides represents a risk for the development of adaptation and cross-adaptation to such compounds.