Abstract: This study aimed to establish a quantitative method for detecting Bifidobacterium in infant formula by using droplet digital polymerase chain reaction (ddPCR). A pair of specific primers and probes were designed targeting the single copy gene rpsL of Bifidobacterium. The reaction conditions of ddPCR were optimized, and the specificity, sensitivity and repeatability of the developed method were investigated and compared with those of the plate counting method. The limit of detection (LOD) was 296 CFU/mL for pure bacterial culture, and 7 300 CFU/g for a simulated sample, respectively. There was no cross-reaction with 10 related species of Lactobacillus, and this method had good repeatability. When Bifidobacteria in commercial infant formula samples were detected by ddPCR and the plate counting method, the deviation between the results of the two methods was less than 10%, indicating good agreement. The ddPCR method can detect Bifidobacteria in infant formula milk powder more quickly, sensitively and accurately than the plate counting method, and it thus has good application prospects.

Key words: droplet digital polymerase chain reaction; plate counting method; Bifidobacterium; quantitative detection; infant formula