Lactobacillus delbrueckii subsp.

lactis is a subspecies of Lactobacillus delbrueckii that is generally used to measure the amount of cobalamin in food.

[1] Its growth rate is proportional to the amount of cobalamin in the growth medium.

However, lactis has been demonstrated to have the option to utilize pseudocobalamin, which is inactive for humans,[2] as well as "alkali-resistant factors" (deoxyribosides and deoxynucleotides),[1] leading to an overestimation of the amount of cobalamine in food.

[3][4] As such, new methods using HPTLC[5] or LC-MS/MS[6] have also been developed.