Effects of exposure to poultry chemical decontaminants on the membrane fluidity of Listeria monocytogenes and Salmonella enteica strains

There is a lack of work comparing the influence of various poultry chemical decontaminants on the membrane fluidity of pathogenic bacteria. In order to assess the possible role of physical membrane changes on bacterial adaptation to decontaminants, fluorescence anisotropy of 1,6-diphenyl-1,3,5-hexatriene (DPH) was measured in Listeria monocytogenes and Salmonella enterica strains before and after growth in the presence of increasing sub-lethal concentrations of decontaminants (trisodium phosphate - TSP, acidified sodium chlorite - ASC, citric acid - CA and peroxyacids - PA). Higher (P<0.05) anisotropy values (lower membrane fluidity) were observed, both before and after exposure to decontaminants, in strains of L monocytogenes (average 0.206 +/- 0.008) than in those of S. enterica (0.188 +/- 0.013). Cells exposed to sub-inhibitory concentrations of acid decontaminants (CA or PA) showed higher (P<0.05) anisotropy values and percentages of survival to acid stress than unexposed cells, suggesting that adaptation to these compounds is related to changes in membrane fluidity. Minimal changes in anisotropy values were observed after growth in presence of TSP or ASC. After treatment with strong concentrations of acid decontaminants (0.05 and 1% ASC. 5% and 10% CA, and 0.1 and 0.25% PA) the highest anisotropy values (highest membrane rigidity) were shown by cells previously grown with sub-inhibitory concentrations of CA or PA, suggesting that the synergistic effects of successive applications of various acids should be minimized. Because of the relationship between high membrane rigidity and high resistance to different stresses, the fact that it is essential to ensure adequate, inhibitory, CA or PA concentrations during poultry decontamination treatments is underlined. (C) 2009 Elsevier B.V. All rights reserved.