Gastrointestinal tract distribution of Salmonella enteritidis in orally infected mice with a species-specific fluorescent quantitative polymerase chain reaction

AIM: To identify and understand the regular distribution pattern and primary penetration site for Salmonella enteritidis (S. enteritidis) in the gastrointestinal tract. METHODS: Based on the species-specific DNA sequence of S. enteritidis from GenBank, a species-specific real-time, fluorescence-based quantitative polymerase chain reaction (FQ-PCR) was developed for the detection of S. enteritidis. We used this assay to detect genomic DNA of S. enteritidis in the gastrointestinal tract, including duodenum, jejunum, ileum, cecum, colon, rectum, esophagus and stomach, from mice after oral infection. RESULTS: S. enteritidis was consistently detected in all segments of the gastrointestinal tract. The jejunum and ileum were positive at 8 h post inoculation, and the final organ to show a positive result was the stomach at 18 h post inoculation. The copy number of S. enteritidis DNA in each tissue reached a peak at 24-36 h post inoculation, with the jejunum, ileum and cecum containing high concentrations of S. enteritidis, whereas the duodenum, colon, rectum, stomach and esophagus had low concentrations. S. enteritidis began to decrease and vanished at 2 d post inoculation, but it was still present up to 5 d post inoculation in the jejunum, ileum and cecum, without causing apparent symptoms. By 5 d post inoculation, the cecum had significantly higher numbers of S. enteritidis than any of the other areas (P < 0.01), and this appeared to reflect its function as a repository for S. enteritidis. CONCLUSION: The results provided significant data for clarifying the pathogenic mechanism of S. enteritidis in the gastrointestinal tract, and showed that the jejunum, ileum and cecum are the primary sites of invasion in normal mice after oral infection. This study will help to further understanding of the mechanisms of action of S. enteritidis.