To establish a microbiological assay for biotin using Lactobacillus plantarum (ATCC8014) in a 96-well microtiter plate, we studied the influence of several pretreated biotin standard solutions on the microbial growth. Then, we measured serum biotin levels by our method, and assessed dietary biotin intake by a 3-day weighed food record to evaluate the biotin status in young Japanese women. A series of pretreatments, including an acid hydrolysis, inhibited growth of the organism. An inverse relationship was observed between growth inhibition and the dilution ratio of biotin standard solutions. These results indicated that biotin standard solutions should be pretreated in a way similar to that of the examination samples. Serum biotin levels (48.3 ± 17.4 μg/mL) were above normal (1.0 μg/mL) and did not change after 14-day biotin supplementation (60 μg/day). Daily biotin intake (48.3 ± 17.4 μg/day) calculated using the German food composition table was higher than the adequate intake (AD; 45 μg/day) of Dietary Reference Intakes for Japanese. There was no correlation between biotin intake and serum biotin level. These results suggest that AD of biotin is sufficient to maintain normal biotin levels. However, further investigations considering other factors such as urine output and supply from enteric bacteria, are necessary to evaluate a more accurate biotin status.
