Table 1.

EC₅₀ values for amino acids and C. difficile UK1 spores.

Amino Acids	C. difficile UK1
	EC50 (mM)
glycine	0.19 ± 0.01
L-alanine	1.1 ± 0.2
taurine	2.5 ± 1.6
L-glutamine	3.1 ± 2.1
L-histidine	4.1 ± 1.6
L-serine	5.6 ± 0.5
L-arginine	6.1 ± 0.6
L-lysine	13.8 ± 1.3
L-threonine	14.4 ± 3.2
D-alanine	15.1 ± 9.1
D-serine	24.3 ± 1.6
L-proline	28.5 ± 5.2
L-methionine	35.2 ± 10.5
D-lysine	72.8 ± 36.1
L-glutamate	98.7 ± 45.6
L-aspartic acid	115 ± 17
L-leucine	>500 mM
L-isoleucine	>500 mM
L-valine	>500 mM
L-phenylalanine	>500 mM
L-tyrosine	Not soluble
L-tryptophan	Not soluble
L-cysteine	Interfered with DPA measurements

EC₅₀ values were calcuated from the germination rate curves as described in the materials and methods. The values reported are the averages from three indepented experiments with the standard deviation from the mean.