Variations in the growth response of four different vitamin B12 assay microorganisms to the same tissue and standard preparations.

Four microbiological assay procedures (Escherichia coli, Lactobacillus leichmanni, Euglena gracilis, and Ochromonas malhamensis) for the vitamin B(12) content of rat liver and kidney tissue were compared. Significant differences in the growth response for portions of the same sample based on the same standard preparations were noted. The liver values with E. coli were strikingly higher than those obtained with the other microorganisms, about which there was rather general agreement. With kidney tissue, E. coli again gave higher values, but not as significantly high as those obtained with L. leichmannii and E. gracilis. O. malhamensis values were significantly lower. These differences were greater than were expected and could not be explained by the differences of specificity and sensitivity of the assay organisms. Several methods of sample preparation, the possible presence of an alkali-heat-stable factor, different methods of sterilization of the sample plus medium, and different chromatographic procedures were explored in an attempt to find explanations for the variations in growth response, with the thought that these various methods would clarify in what form or forms the free and bound vitamin B(12) might exist in the samples. No clear-cut explanation was found.