A modification of the Colowick and Womack procedure for measuring ligand binding by macromolecules is described for drug binding by bacteria. This technique is based on the determination of drug concentration in the dialysate from a bacteria-drug mixture at equilibrium. The dialysis cell of the original procedure was replaced by a Minibeaker (Bio-Rad), which has a larger membrane surface area, and the dialysate was continuously monitored with a spectrophotometer equipped with a flow cell. With this system, only 3 min was required to determine the amount of cetylpyridinium chloride bound by Escherichia coli K-12 strain P678. Possible applications of the technique are discussed.

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Bacillus subtilis 5230 spores were lyophilized in 0.067 M phosphate buffer and stored at 2 to 80C for 9 to 27 months. The lyophilized spores were reconstituted with buffer or 0.9% saline, and the heat resistance was determined in a thermoresistometer. Lyophilization had no effect on the heat resistance of the spores but did result in a slight decrease in population (0.3-logarithm reduction). The lyophilized spores maintained heat resistance and population levels over the test periods. The D-values ranged from 0.44 to 0.54 min at 121.10C, and the z-values ranged from 6.1 to 6.6°C. Lyophilization was concluded to be an acceptable alternative for storage of bacterial spores that are to be used as biological indicators in sterilization processes.

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A modification of the Colowick and Womack procedure for measuring ligand binding by macromolecules is described for drug binding by bacteria. This technique is based on the determination of drug concentration in the dialysate from a bacteria-drug mixture at equilibrium. The dialysis cell of the original procedure was replaced by a Minibeaker (Bio-Rad), which has a larger membrane surface area, and the dialysate was continuously monitored with a spectrophotometer equipped with a flow cell. With this system, only 3 min was required to determine the amount of cetylpyridinium chloride bound by Escherichia coli K-12 strain P678. Possible applications of the technique are discussed.