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

Quantitative distribution and interaction of Salmonella Zega with host cells in visceral organs of chickens infected orally, intraperitoneally and per cloaca

Immunohistochemical study of the visceral organs of chickens experimentally infected with Salmonella Zega by three routes was carried out to compare the quantitative distribution and interaction of the organism with host cells. 100 birds comprising of 2 week-old chickens were divided into 4 groups of 25 each. Group A was inoculated orally, group B intraperitoneally, group C were administered per cloaca and D were not inoculated and served as control. All the infected birds were inoculated with 0.2 ml of 1 × 108 cfu of the bacteria. Two birds from each group were sacrificed every 24 h post infection. Samples of visceral organs were collected for immunohistochemistry. The distribution of Salmonella Zega in every organ was taken as Mean ± SD of the number of foci of immunoreactions and Compared using a 2-way ANOVA. The interaction of Salmonella Zega with host cells was determined by taking the percentage of the days post infection in which immunoreactions were detected in host cells in each route of infection. The distribution of the organism was highest in the lung of intraperitoneally infected chickens (83.95 ± 27.89) and lowest in the heart (5.21 ± 3.65) of chickens that were infected per cloaca. The highest percentage of interaction of Salmonella Zega was recorded in the epithelial (100%) and blood (100%) cells in all the routes of infection. There were variations in the distribution of Salmonella Zega in visceral organs of chickens but the level of interactions with host cells were similar even when infected through different routes.

Persistent salmonellosis causes pancreatitis in a murine model of infection

Pancreatitis, a known risk factor for the development of pancreatic ductal adenocarcinoma, is a serious, widespread medical condition usually caused by alcohol abuse or gallstone-mediated ductal obstruction. However, many cases of pancreatitis are of an unknown etiology. Pancreatitis has been linked to bacterial infection, but causality has yet to be established. Here, we found that persistent infection of mice with the bacterial pathogen Salmonella enterica serovar Typhimurium (S. Typhimurium) was sufficient to induce pancreatitis reminiscent of the human disease. Specifically, we found that pancreatitis induced by persistent S. Typhimurium infection was characterized by a loss of pancreatic acinar cells, acinar-to-ductal metaplasia, fibrosis and accumulation of inflammatory cells, including CD11b+ F4/80+, CD11b+ Ly6Cint Ly6G+ and CD11b+ Ly6Chi Ly6G- cells. Furthermore, we found that S. Typhimurium colonized and persisted in the pancreas, associated with pancreatic acinar cells in vivo, and could invade cultured pancreatic acinar cells in vitro. Thus, persistent infection of mice with S. Typhimurium may serve as a useful model for the study of pancreatitis as it relates to bacterial infection. Increased knowledge of how pathogenic bacteria can cause pancreatitis will provide a more integrated picture of the etiology of the disease and could lead to the development of new therapeutic approaches for treatment and prevention of pancreatitis and pancreatic ductal adenocarcinoma.

Gallstones play a significant role in Salmonella spp. gallbladder colonization and carriage

Salmonella enterica serovar Typhi can colonize the gallbladder and persist in an asymptomatic carrier state that is frequently associated with the presence of gallstones. We have shown that salmonellae form bile-mediated biofilms on human gallstones and cholesterol-coated surfaces in vitro. Here, we test the hypothesis that biofilms on cholesterol gallbladder stones facilitate typhoid carriage in mice and men. Naturally resistant (Nramp1(+/+)) mice fed a lithogenic diet developed cholesterol gallstones that supported biofilm formation during persistent serovar Typhimurium infection and, as a result, demonstrated enhanced fecal shedding and enhanced colonization of gallbladder tissue and bile. In typhoid endemic Mexico City, 5% of enrolled cholelithiasis patients carried serovar Typhi, and bacterial biofilms could be visualized on gallstones from these carriers whereas significant biofilms were not detected on gallstones from Escherichia coli infected gallbladders. These findings offer direct evidence that gallstone biofilms occur in humans and mice, which facilitate gallbladder colonization and shedding.

Spontaneous excision of the Salmonella enterica serovar Enteritidis-specific defective prophage-like element phiSE14

Salmonella enterica serovar Enteritidis has emerged as a major health problem worldwide in the last few decades. DNA loci unique to S. Enteritidis can provide markers for detection of this pathogen and may reveal pathogenic mechanisms restricted to this serovar. An in silico comparison of 16 Salmonella genomic sequences revealed the presence of an approximately 12.5-kb genomic island (GEI) specific to the sequenced S. Enteritidis strain NCTC13349. The GEI is inserted at the 5' end of gene ydaO (SEN1377), is flanked by 308-bp imperfect direct repeats (attL and attR), and includes 21 open reading frames (SEN1378 to SEN1398), encoding primarily phage-related proteins. Accordingly, this GEI has been annotated as the defective prophage SE14 in the genome of strain NCTC13349. The genetic structure and location of phiSE14 are conserved in 99 of 103 wild-type strains of S. Enteritidis studied here, including reference strains NCTC13349 and LK5. Notably, an extrachromosomal circular form of phiSE14 was detected in every strain carrying this island. The presence of attP sites in the circular forms detected in NCTC13349 and LK5 was confirmed. In addition, we observed spontaneous loss of a tetRA-tagged version of phiSE14, leaving an empty attB site in the genome of strain NCTC13349. Collectively, these results demonstrate that phiSE14 is an unstable genetic element that undergoes spontaneous excision under standard growth conditions. An internal fragment of phiSE14 designated Sdf I has been used as a serovar-specific genetic marker in PCR-based detection systems and as a tool to determine S. Enteritidis levels in experimental infections. The instability of this region may require a reassessment of its suitability for such applications.

Replication kinetics of Salmonella enteritidis in internal organs of ducklings after oral challenge: a quantitative time-course study using real-time PCR

This research was undertaken to understand the replication kinetics of Salmonella enteritidis (S. enteritidis) in the internal organs of ducklings after oral challenge over a 2 wk period. A serovar-specific real-time, fluorescence-based quantitative polymerase chain reaction (FQ-PCR) assay was used to detect genomic DNA of S. enteritidis in the blood and the internal organs at different time points respectively. 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 and kidney were positive at 20 h PI, and the final organ to show a positive results was the gallbladder at 22 h PI. The copy number of S. enteritidis DNA in each tissue reached a peak at 24 h-36 h PI, with the liver and spleen containing the highest concentration of S. enteritidis. 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 2 wk for the spleen without causing apparent symptoms. To make the results meaningful, a side-by-side bacteriology method (IFA) was performed. The results of IFA were similar to the FQ-PCR assay. This research provided a significant data for understanding the life cycle of S. enteritidis in the internal organs, and may help to understand the pathogenesis of S.entertidis in the future.