Quantitative studies of the regular distribution pattern for Salmonella enteritidis in the internal organs of mice after oral challenge by a specific real-time polymerase chain reaction

Abstract

Aim: To identify and understand the regular distribution pattern for Salmonella enteritidis (S. enteritidis) in the internal organs of mice after an oral challenge over a 3 wk period.

Methods: Assays based on the serovar-specific DNA sequence of S. enteritidis from GenBank, and a serovar-specific real-time, fluorescence-based quantitative polymerase chain reaction (FQ-PCR) were developed for the detection of S. enteritidis. We used this assay to detect genomic DNA of S. enteritidis in the blood and the internal organs, including heart, liver, spleen, kidney, pancreas, and gallbladder, from mice after oral challenge at different time points respectively.

Results: The results showed that the spleen was positive at 12 h post inoculation (PI), and the blood was at 14 h PI. The organism was detected in the liver and heart at 16 h PI, the pancreas was positive at 20 h PI, and the final organs to show positive results were the kidney and gallbladder at 22 h PI. The copy number of S. enteritidis DNA in each tissue reached a peak at 24-36 h PI, with the liver and spleen containing high concentrations of S. enteritidis, whereas the blood, heart, kidney, pancreas, and gallbladder had low concentrations. S. enteritidis populations began to decrease and were not detectable at 3 d PI, but were still present up to 12 d PI in the gallbladder, 2 wk for the liver, and 3 wk for the spleen without causing apparent symptoms.

Conclusion: The results provided significant data for understanding the life cycle of S. enteritidis in the internal organs, and showed that the liver and spleen may be the primary sites for setting itself up as a commensa over a long time after oral challenge. Interestingly, it may be the first time reported that the gallbladder is a site of carriage for S. enteritidis over a 12 d period. This study will help to understand the mechanisms of action of S. enteritidis infection in vivo.

Figure 1

Used the standards DNA template with 10-fold serial dilutions to develop standard curve. A: Amplification curve; B: Standard curve; 1, 1.0 × 10¹⁰ copies/μL; 2, 1.0 × 10⁹ copies/μL; 3, 1.0 × 10⁸ copies/μL; 4, 1.0 × 10⁷ copies/μL; 5, 1.0 × 10⁶ copies/μL; 6, 1.0 × 10⁵ copies/μL.