Analytical Microbiology

Abstract

This chapter presents the theory of antibiotic inhibition zones. It discusses the sequence of events that may occur when an antibiotic diffuses through agar in which bacterial cells capable of multiplying in the medium are present. A large number of factors influence the size of antibiotic inhibition zones that are analyzed with the existing data into effects upon the factors in the formula relating critical time to the growth of the organism and to the diffusion of the antibiotic. Critical time is the time required for the population, critical population, to increase to a particular value. It is the amount of antibiotic absorbed by this critical population that determines the zone edge, and this amount adsorbed on the cell receptors is in equilibrium with the minimum inhibitory concentration outside the cells. In a diffusing system, the critical concentration has to provide both adsorbed and free antibiotic.