Quantitative aspects of phenyl substituted alcohol and ether bacteriostatic interaction with Escherichia coli B/5

It is well established that compounds of the class phenylalkane alcohols and ethers exert their antimicrobial action on the bacterial envelope--probably on the membrane. However, the overall stoichiometry, the number of molecules bound vs those merely added per cell, and the kinds of equilibria involved (site binding vs equipartitioning) are not clear. This work examines antimicrobial action on E. coli B/5 with eight such compounds. Directly determined binding data, plate counting viabilities, radiorespirometry, and microcalorimetry of glucose utilization were evaluated. The compounds mostly bind by simply equipartitioning, up to some threshold level, short of kill. That level depends sharply on the number of alkane carbons in the phenyl alkane derivative, but not on the precise structure. Past the threshold, bacteriostatic action is sudden and complete, probably reflecting cooperative behaviour in the cell envelope. The amount of bound compound at the threshold level is only about 0.5 to 3% of the weight of the bacterial envelope hydrocarbon, when bacteriostasis occurs. There is an unexpectedly small dependence on cell concentration. The principal governors on where the monooxygen phenylalkanes kill cells seems to be merely their concentration or chemical potential, the number of aliphatic carbons, and the binding mechanism. Because of the cell concentration independence, the cells act as if they constituted a second phase, relative to the solution. Results from the microcalorimetric method for assay of bacteriostasis correlate well with those from plate counting or viability assays.