Quantitative strain‐specific detection of Lactobacillus rhamnosus GG in human faecal samples by real‐time PCR

Aims:  To develop a strain‐specific rapid assay for identification and quantification of Lactobacillus rhamnosus GG in human faecal samples. Methods and Results:  A unique random amplified polymorphic DNA (RAPD) band of the L. rhamnosus GG strain was isolated and sequenced. Strain‐specific polymerase chain reaction (PCR) primers and probes were designed based on the sequence. Quantification was performed by the real‐time PCR using a fluorescent resonance energy transfer (FRET) system. The specificity of the assay was tested with DNA isolated from a set of known strains and human faecal samples. The analytical sensitivity of the method for L. rhamnosus GG was about 10 CFU per assay, which corresponds to 10 5  CFU g −1 of wet faeces. Conclusions:  Quantitative real‐time PCR is a suitable method for strain‐specific identification of L. rhamnosus GG in human faecal samples. Significance and Impact of the Study:  Lactobacillus rhamnosus GG is one of the most studied probiotic strains in clinical trials but still lacks a DNA‐based identification method. This study describes a real‐time PCR method for strain‐specific identification and quantification of L. rhamnosus GG in human faecal samples.