Brown K J, Lines D R
Aust J Exp Biol Med Sci. 1978 Aug;56(4):507-11. doi: 10.1038/icb.1978.57.
Variation in the inhibition of growth of Escherichia coli and Shigella sp. in various media containing beta-2-thienylalanine was attributed to differences in concentrations of Mg++ ions. Random blood samples 112 infants were tested for elevated phenylalanine in the phenylketonuria (PKU) screening assay. Magnesium ion levels also affected the results of this assay. At 0.05 g/1 MgSO4, the concentration present in commerical PKU test agar, four false positives were detected, while no readings could be made due to overgrowth of the Bacillus subtilis test strain when the concentration was increased to 0.1 g/1.
