ROD21 excision frequency increases when S. Enteritidis infects phagocytic cells.

Bone marrow-derived DCs (A) and J774.3 macrophages (B) were infected with S. Enteritidis (MOI equal to 25). After 2, 18 and 24 h post infection (hpi) intracellular bacteria were recovered and the copy number of the attB sequence generated by type 1 excision was detected by quantitative PCR, using as template the genomic DNA obtained from intracellular bacteria. Frequency of excision is expressed as the ratio between the copy number of the attB-1 sequence determined for intracellular and extracellular bacteria. The DNA amount was normalized by calculating the copy number of the rpoD gene. Data shown in graphs are average values of at least three independent experiments. The amount of intracellular bacteria recovered after 2, 18 and 24 hpi from DCs (C) and J774.3 (D) was determined by lysing either 1,000 DCs or 100 J774.3 cells with PBS-triton X100 (0.1%) and seeding the lysates in LB plates. Data shown are the average of at least 3 independent experiments.