1980 Volume 24 Issue 7 Pages 603-615
Growth comparisons were made, using Shigella, Escherichia, and Salmonella cultures, in liquid and agar-solidified defined media containing β-2-thienylalanine (β-2-t). The comparisons were performed to determine the nature of growth inhibition by β-2-t under different physical growth conditions.
In a plate assay, with increasing β-2-t mixed into the agar, inhibition of Escherichia and Shigella increased. However, Salmonella cultures were not inhibited even at the highest β-2-t concentrations used. With β-2-t added to liquid cultures, however, dose-response growth relationships were exhibited by all three genera.
The differences occurring in β-2-t inhibition between liquid and plate assay conditions were not due to composition of culture plates, time of challenge of cultures with β-2-t, availability of oxygen and associated differences in ratios of volume of media to available surface area, selection of mutants in the plate assay, or to extractable substances from the agar.
However, when β-2-t diffusion into the liquid medium was delayed by using agar plug diffusion cultures, a physiological mechanism was demonstrable which largely protected Salmonella cultures, but not Escherichia and Shigella cultures, from growth inhibition.
