Abstract
An enzymatic method was developed for the simple and rapid assay of lactobacilli. A glucose-hexokinase system was used to remove extracellular ATP, and intracellular ATP was assayed with the luciferin-luciferase system using luciferase commercially prepared from fireflies. Freeze-dried powders of Streptococcus faecalis (SF), Lactobacillus bifidus (LB) and erythromycin-resistant Lactobacillus acidophilus (LA-E) were used as the samples. Prior to assay the freeze-dried powder of lactobacilli was incubated at 37°in a glucose-peptone-yeast extract medium to increase the amount of intracellular ATP. Using the proposed system, the intracellular ATP levels of SF, LA-E and LB were about 100, 80 and 800 times those obtained with the conventional system, respectively. The detection limit was 1.0×105 cells/0.1 ml. Reproducibility was 6.0-9.9% (coefficient of variation). This method was found to be extremely sensitive compared with the conventional luciferin-luciferase system and is convenient because it does not require sterilization and can be completed within a day. This method seems suitable for routine application in survival tests of lactobacilli.
