Rapid Antibacterial Activity of 2 Novel Hand Soaps: Evaluation of the Risk of Development of Bacterial Resistance to the Antibacterial Agents

Abstract

To evaluate the antimicrobial efficacy of and risk of organisms developing resistance to 2 novel hand soaps: (1) a soap containing triclosan, polyhexamethylene biguanide, and benzethonium chloride added to a soap base (TPB soap); and (2) a soap containing farnesol, polyhexamethylene biguanide, and benzethonium chloride added to a soap base (FPB soap). Tests also included soaps containing only triclosan. The risk of emergence of resistant bacterial mutants was investigated by determining the susceptibility changes after repeated exposure of bacteria to the drugs and soaps in vitro. The effectiveness of the soaps was evaluated using an in vitro tube dilution method, a volunteer method (the ASTM standard), and 2 pig skin methods. The minimum inhibitory concentration and minimum bactericidal concentration of triclosan against Staphylococcus aureus increased 8- to 62.5-fold, whereas those of TPB and FPB (both alone and in soap) were unchanged. In vitro, TPB and FPB soaps produced higher log(10) reductions in colony-forming units of all tested organisms (4.95-8.58) than did soaps containing triclosan alone (0.29-4.86). In the test using the pig skin and volunteer methods, TPB soap produced a higher log(10) reduction in colony-forming units (3.1-3.3) than did the soap containing triclosan alone (2.6-2.8). The results indicate that TPB and FPB soaps may provide superior rapid and broad-spectrum efficacy with a lower risk of organisms developing resistance than do soaps containing triclosan alone. Pig skin methods may be used to predict the efficacy of antibacterial soaps in the rapid disinfection of contaminated hands. Hand washing with TPB and FPB soaps by healthcare workers and the general population may reduce the transmission of pathogens, with a lower risk of promoting the emergence of resistant organisms.