Rapid determination of vitamin B_2 secretion by bacteria growing on solid media

摘要

Aims: Development of an agar-diffusion assay to measure vitamin B_2 in biological samples and application of the method to determine the amount of vitamin B_2 secreted by bacteria. Methods and Results: A riboflavin-auxotrophic mutant of Bacillus cereus was generated by mini-Tn10 insertion in the ribD gene. ribD mutant sensitivity to exogenous vitamin B_2 was investigated by turbidimetric and agar-diffusion assays. In turbidimetric assays, the B. cereus mutant displayed a similar level of sensitivity to vitamin B_2 to that of Lactobacillus casei ATCC 7469, the reference organism used for microbiological vitamin B_2 quantification. However, only the ribD mutant could be used as an indicator organism in agar-diffusion assays. A total of eight probiotic strains, fro five different probiotic formulations, were analysed by the ribD mutant-based assay on agar plates in order to determine their ability to secrete vitamin B_2 during growth. Conclusion: The agar diffusion method with the ribD mutant of B. cereus is highly reproducible, sensitive, rapid, inexpensive, and can be applied to measure the amount of vitamin B_2 in different samples. Significance and Impact of the Study: The method developed in this study appears to be a good candidate for the screening of vitamin B_2 secretion by bacteria growing on solid media.