Abstract: Objective: To establish a real-time fluorescent quantitative PCR assay for the rapid and accurate detection of Lactobacillus acidophilus in probiotic beverages. Methods: Specific primers and probes were designed based on the conserved SPIDR region of L. acidophilus NCFM. The established method was assessed with respect to specificity, sensitivity and reproducibility, and it was applied to model and commercial samples. Results: The method had good specificity. The absolute sensitivity was 3 pg and the relative sensitivity was 103 CFU/mL. The repeatability expressed as relative standard deviation (RSD) was below 2.6%. At the same time, the amplification was not affected by the coexistence of pure genome or culture of Escherichia coli, indicating that the method has good anti-interference ability. This method showed good linearity (R2 = 0.987) and it was feasible to detect actual samples. Of 11 commercial samples, 6 contained L. acidophilus strains while the rest did not. L. acidophilus was detected in all samples labeled with L. acidophilus in the range of 5.83 × 102 to 3.68 × 104 CFU/mL. Conclusion: The real-time fluorescence quantitative PCR method can quickly and accurately detect L. acidophilus in probiotic beverages.

Key words: real-time fluorescence quantitative PCR, Lactobacillus acidophilus, quantitative, detection