Sites of action by propionate on Listeria monocytogenes

Exposure of Listeria monocytogenes to a solution of sodium propionate (8% w/v) for 60 min caused 87% of the population to be injured. Injury was evidenced by inability of the bacterium to tolerate 6% sodium chloride in tryptose agar as compared to ability to grow on tryptose agar with no added salt. Injured cells were allowed to repair in tryptose broth and the repair process was studied by addition to tryptose broth of sublethal amounts of metabolic or synthetic inhibitors. Repair of injured cells did not require electron transport or synthesis of cell wall components, mRNA or protein. No changes which may have occurred in the cell membrane of injured cells, allowed leakage of proteins or nucleotides into the medium. Exogenous cation salts enhanced the rate of recovery of injured cells. The specific activity of lactic dehydrogenase was reduced in propionate-injured L. monocytogenes.