In this simplified microbiological assay for serum vitamin B12, Lactobacillus leichmanii (NCIB 8117) adapted to tolerate high concentrations (500 mg/L) of the polymyxin antibiotic colistin sulfate is used. Results were similar in parallel experiments in which we used both the parent strain of L. leichmanii (NCIB 8117), and the new adapted strain. Evaluation of assay performance showed excellent...

A comparison has been made of the radioisotope dilution-coated charcoal method and a microbiological assay (with L. leichmannii as test organism) for determining the concentration of vitamin B(12) in serum. A satisfactory correlation was found between the results of the two methods. Under appropriate conditions the reproducibility of the radioisotope method compared favourably with that of the ...