A two-step approach for enhancing the efficacy of trisodium phosphate (TSP) was evaluated using meat spoilage and pathogenic bacteria in flow cell biofilms and adipose tissue model systems. The process was based on the plasmolysis of attached bacteria (biofilms) with a hyperosmotic solution (1.5 M NaCl) and the subsequent deplasmolysis of cells with a low-osmotic-strength solution containing different concentrations of TSP (0.1, 0.25, 0.5, 0.625, and 1.0% [wt/vol]). Escherichia coli, Salmonella Enteritidis, Pseudomonas sp., Listeria monocytogenes, and Brochothrix thermosphacta strains were cultivated for 24 h as pure culture biofilms in glass flow cells with complex media and were then treated with either 0.1, 0.25, 0.5, 0.625, and 1.0% TSP, or the same TSP concentrations delivered in conjunction with plasmolysis-deplasmolysis (PDP). Confocal scanning laser microscopy, a commercial fluorescent viability probe, and image analysis were then used to quantify the relative abundances of living and dead cells remaining after the different treatment regimes. With the exception of L. monocytogenes (which was resistant to TSP concentrations of up to 5%), the PDP process increased the sensitivity of the test strains to TSP. However, when similar experiments were conducted with pork adipose tissue, it became evident that higher TSP concentrations were necessary to produce significant decreases in the number of viable cells and that the PDP process generally failed to enhance TSP efficacy. An exception was L. monocytogenes, which exhibited an increase in sensitivity to TSP when inoculated tissue was pretreated with 1.5 M NaCl. It is thought that factors contributing to the failure of the PDP process to enhance the activity of TSP in meat systems involves the mode of TSP antimicrobial activity, alkaline pH stress, and the chemically complex, buffered nature of meats. It remains to be determined whether the PDP process is suitable for use with other food grade antimicrobial agents or can be used in nonfood biofilm control applications.

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