Specific detection of a probiotic Lactobacillus strain in faecal samples by using multiplex PCR

Lactobacillus gasseri 4B2 is a human isolate characterised by a strong autoaggregating phenotype mediated by APF (aggregation-promoting factor), a secreted protein. Two primer pairs were developed for simultaneous amplification of a specific fragment of the APF gene and a highly conserved region of the 16S rRNA gene. The specificity of this protocol was checked in DNA samples isolated from single and mixed cultures of Lactobacillus. The same amplification protocol was successfully used directly adding whole bacterial cells to PCR reaction tubes. The suitability of this method for in vivo studies was investigated through feeding L. gasseri 4B2 to mice and analysing colony forming units obtained by plating faecal samples on selective medium. The methodology allows a fast and reliable identification of the target strain without any DNA extraction procedure.