Multiple parameters for the comprehensive evaluation of the susceptibility of Escherichia coli to the silver ion.

The susceptibility of Escherichia coli B to the antibacterial activity of silver ions was measured in terms of the initial inhibitory concentration, complete inhibitory concentration, postagent effect for bacteriostatic susceptibility, minimum bactericidal concentration, maximum tolerant concentration, and log killing time for bactericidal activity. At a concentration of 9.45 microM and an inoculum size of 10(4-5) CFU ml-1, silver caused growth delay of E. coli; at a concentration of 18.90 microM, silver completely inhibited bacterial growth. Prolonged postagent effects ranged between 1.5 and 12 h at 0.75 x the initial inhibitory concentration, 1.0 x the initial inhibitory concentration, and 1.5 x the initial inhibitory concentration of the silver ion. One log-unit of viable bacterial population size was lost every 30 min at the minimum bactericidal concentration of the silver ion. Silver tolerance was determined as 20 times the initial inhibitory concentration with 48 h of exposure. This study presents an evaluative model as a reference for the quantitative analysis of the susceptibility of bacteria to silver ions.