Table 1. Minimum D-amino acid concentration required to prevent^* germination by its equivalent L-amino acid.

	D-amino acid concentration
L-amino acid/concentration	C. sporogenes	C. botulinum
L-alanine/1 mM	10 mM	100 mM
L-cysteine/10 mM	100 mM	100 mM
L-serine/10 mM	20 mM	100 mM
L-phenylalanine/10 mM	20 mM	NT
L-methionine/10 mM	100 mM	100 mM

Tests were conducted in 20 mM Tris buffer, pH 7.4, L-amino acid (1–10 mM), D-amino acid (10–100 mM) + L-lactate (50 mM) and NaHCO₃ (50 mM) at 30°C. NT = D-phenylalanine was not inhibitory at 20 mM and could not be tested at a higher concentration due to low solubility.

*Defined as a <10% fall in OD₆₀₀, equating to <1% germination observed microscopically.