microbiology, Vol 145, 643-654, Copyright © 1999 by Society for General Microbiology
Diffusion through agar blocks of finite dimensions: a theoretical analysis of three systems of practical significance in microbiology [In Process Citation]
AL Koch
Biology Department, Indiana University, Bloomington 47405-6801, USA. Koch@Indiana.edu
A number of experimental methods in biology depend on the kinetics of
diffusion of a substance through a gel. This paper reviews the diffusion
equations, gives the experimental limitations for some useful cases, and
presents computer simulations for cases that cannot be treated
analytically. While double diffusion is not considered, three
single-diffusion situations are treated. (1) Systems for the study of
chemotaxis in the gliding bacterium Myxococcus xanthus. Experimental
designs used for this in many cases in the literature were inappropriate
and mathematical analysis of these is presented. (2) The development of
gradient plates. The time necessary for vertical diffusion to become
substantially complete and before diffusion in the direction of the
original slant has proceeded significantly is calculated. (3) The
application to antimicrobial disk susceptibility tests. The basis of the
measurement of antibiotic sensitivities with disks containing antimicrobial
agents, as routinely used in clinical microbiological and testing
laboratories, is analysed and the limitations are assessed and improvements
suggested.
