In vitro model simulating the form of exposure of bacteria to antimicrobial drugs encountered in infection.

A new model, which is designed to investigate the in vitro activity of antibiotics as a function of different concentration-time curves, is described. The antibiotic is allowed to diffuse through a membrane into a bacterial culture until a peak level is reached; the antibiotic is then removed by flow-assisted back diffusion. With this arrangement it is possible to expose bacteria to a changing concentration of drug while maintaining a constant volume of bacterial culture. Preliminary studies were carried out to investigate the response of a strain of Escherichia coli to gentamicin. The results indicate that bacteria surviving exposure to concentrations of gentamicin similar to those obtained during therapy may exhibit an increase in resistance to the antibiotic.