Distribution of "classic" virulence factors among Salmonella spp.

Whether an infection with Salmonella spp. leads to a disease largely depends on the virulence of the strain and the constitution of the host. The virulence of the strain is determined by so-called virulence factors. Whereas a number of virulence factors of Salmonella have been identified only recently, others have been studied for decades. These latter virulence factors i.e., virulence-plasmids, toxins, fimbriae and flagella are therefore referred to as "classic" virulence factors. Here we present an overview on the distribution of (genes coding for) these virulence factors among Salmonella spp. The pathogenicity islands of Salmonella are also reviewed, all be it briefly, since they contain a major part of the virulence genes.

The heat shock response and cytoprotection of the intestinal epithelium.

Following heat stress, the mammalian intestinal epithelial cells respond by producing heat shock proteins that confer protection under stressful conditions, which would otherwise lead to cell damage or death. Some of the noxious processes against which the heat shock response protects cells include heat stress, infection, and inflammation. The mechanisms of heat shock response-induced cytoprotection involve inhibition of proinflammatory cytokine production and induction of cellular proliferation for restitution of the damaged epithelium. This can mean selective interference of pathways, such as nuclear factor kappa B (NF-kappaB) and mitogen-activated protein kinase (MAPK), that mediate cytokine production and growth responses. Insight into elucidating the exact protective mechanisms could have therapeutic significance in treating intestinal inflammations and in aiding maintenance of intestinal integrity. Herein we review findings on heat shock response-induced intestinal epithelial protection involving regulation of NF-kappaB and MAPK cytokine production.

Expression levels of heat shock proteins in enterocyte-like Caco-2 cells after exposure to Salmonella enteritidis.

The enterocytes of the small intestine are occasionally exposed to pathogenic bacteria, such as Salmonella enteritidis 857, an etiologic agent of intestinal infections in humans. The expression of the heat shock response by enterocytes may be part of a protective mechanism developed against pathogenic bacteria in the intestinal lumen. We aimed at investigating whether S. enteritidis 857 is able to induce a heat shock response in crypt- and villus-like Caco-2 cells and at establishing the extent of the induction. To establish whether S. enteritidis 857 interfered with the integrity of the cell monolayer, the transepithelial electrical resistance (TEER) of filter-grown, differentiated (villus-like) Caco-2 cells was measured. We clearly observed damage to the integrity of the cell monolayer by measuring the TEER. The stress response was screened in both crypt- and villus-like Caco-2 cells exposed to heat (40-43 degrees C) or to graded numbers (10(1)-10(8)) of bacteria and in villus-like cells exposed to S. enteritidis 857 endotoxin. Expression of the heat shock proteins Hsp70 and Hsp90 was analyzed by polyacrylamide gel electrophoresis and immunoblotting with monoclonal antibodies. Exposure to heat or Salmonella resulted in increased levels of Hsp70 and Hsp90 in a temperature-effect or Salmonella-dose relationship, respectively. Incubation of Caco-2 cells with S. enteritidis 857 endotoxin did not induce heat shock gene expression. We conclude that S. enteritidis 857 significantly increases the levels of stress proteins in enterocyte-like Caco-2 cells. However, our data on TEER clearly indicate that this increase is insufficient to protect the cells.

Ventilator-induced heat shock protein 70 and cytokine mRNA expression in a model of lipopolysaccharide-induced lung inflammation.

OBJECTIVE: To investigate the effect of mechanical ventilation with no PEEP (ZEEP) and 4 cmH(2)O PEEP on heat shock protein 70 (HSP70) and pulmonary inflammatory cytokine expression in a model of lipopolysaccharide (LPS) induced lung inflammation. DESIGN AND SETTING: Prospective, randomized, experimental animal study. SUBJECTS AND INTERVENTIONS: We challenged 42 male Sprague-Dawley rats intratracheally with LPS. After 24 h the rats were randomly assigned to one of the ventilation strategies. Rats received either 4 h of mechanical ventilation with ZEEP or mechanical ventilation with 4 cmH(2)O PEEP. A nonventilated control group received LPS only. Lung pathology after LPS challenge was evaluated by histology to assess baseline lung injury. HSP70 and cytokine mRNA levels were measured in total lung homogenates. RESULTS: PaO(2) levels and lung histology revealed no deterioration after PEEP ventilation and severe deterioration after ZEEP ventilation. There was a significant higher expression of HSP70 and IL-1beta mRNA in the lungs of the ZEEP group than in the PEEP group and nonventilated controls. In the ZEEP group high HSP70 levels were correlated inversely with low IL-1beta mRNA and low IL-6 mRNA. CONCLUSIONS: We propose that HSP70 expression protects the lung against ventilator-induced lung injury by decreasing cytokine transcription in the lung.

Reduced life expectancy in rats after neonatal dexamethasone treatment.

The glucocorticoid dexamethasone (Dex) is widely used in preterm infants for the prevention of chronic lung disease. However, major concern has arisen about the long-term sequelae of this therapy. Here we report that neonatal treatment with dexamethasone significantly shortens the lifespan by 25% of male rats (28.6 +/- 1.1 to 21.3 +/- 0.8 mo) and by 18% of female rats (26.9 +/- 1.8 to 22.0 +/- 0.7 mo). Histopathological examination indicated end-stage cardiac and renal failure as the cause of premature death. Furthermore, Dex-treated rats showed symptoms of hypertension at young adult age, which worsened with increasing age. Thus, a brief period of glucocorticoid treatment during early life results in untimely death presumably due to cardiovascular and renal disease later in life. These serious, adverse long-term consequences call for prudence with glucocorticoid treatment of human preterm infants and careful follow-up of young adults with a history of neonatal glucocorticoid treatment.

Effects of subtotal colectomy on bacterial translocation during experimental acute pancreatitis.

OBJECTIVES: The colon is considered a major source of bacteria causing infection of pancreatic necrosis in acute pancreatitis (AP). Subtotal colectomy before AP in rats reduces mortality, but its role in affecting small bowel flora, bacterial translocation, and infection of pancreatic necrosis is unknown. Our aim was to study these phenomena in rats with AP. METHODS: Fifty rats, allocated in 4 groups, underwent 2 laparotomies: group 1, sham laparotomy and saline biliopancreatic duct infusion; group 2, subtotal colectomy and saline infusion; group 3, sham laparotomy and AP (ductal infusion of glycodeoxycholic acid and intravenous cerulein); group 4, subtotal colectomy and AP. Seventy-two hours later, samples were collected for microbiological analysis. RESULTS: Subtotal colectomy caused small bowel bacterial overgrowth with gram-positive cocci (group 1 versus group 2, duodenum: P = 0.030, ileum: P = 0.029). Bacterial counts of gram-negative rods/anaerobes in the duodenum and ileum and pancreatic bacterial counts of rats with colectomy and AP were significantly higher than in rats with AP only (group 3 versus group 4, duodenum: P = 0.040, ileum: P = 0.029, pancreas: P = 0.017). Duodenal bacterial overgrowth and pancreatic infection correlate significantly (r = 0.45, P = 0.004). CONCLUSIONS: Subtotal colectomy induces small bowel bacterial overgrowth, which is associated with increased bacterial translocation to the pancreas.

Cholesterol crystals enhance and phospholipids protect against pancreatitis induced by hydrophobic bile salts: a rat model study.

OBJECTIVES: The role of bile composition in the pathogenesis of biliary pancreatitis is unknown. The objective of this experiment was to explore the potential role of bile salts, phospholipids, and cholesterol crystals in the pathogenesis of biliary pancreatitis in a rat model. METHODS: Model systems composed of taurodeoxycholate (TDC), mixed bile salts (MBS), or tauroursodeoxycholate (TUDC) [in 10 mM phosphate-buffered saline (PBS), pH 7.4], with or without cholesterol crystals or phosphatidylcholine, were infused into bile ducts of male Sprague-Dawley rats. Twenty-four hours later, animals were killed for histopathologic scoring of (peri)pancreatic inflammation. RESULTS: : Severity of acute pancreatitis depended on bile salt hydrophobicity (TDC > MBS >> TUDC = PBS; histopathologic scores: 25.6 +/- 0.5, 23.0 +/- 1.5, 14.4 +/- 2.2, 14.8 +/- 1.0, respectively; P < 0.001), with corresponding differences in serum lipase concentration. Phosphatidylcholine protected against detrimental effects of TDC at physiological, but not at low, concentrations (scores: 19.5 +/- 2.3 vs 28.3 +/- 1.9 in case of Phosphatidycholine/(TDC + Phosphatidycholine) ratios 0.25 or 0.05, respectively). Cholesterol crystals increased severity of pancreatitis in model systems containing TDC or MBS, but not TUDC or PBS (33.2 +/- 0.4, 29.6 +/- 1.2, 18.6 +/- 1.5, 18.5 +/- 2.2, respectively; P < 0.001). CONCLUSIONS: In the rat model, hydrophobic bile salts and cholesterol crystals aggravate biliary pancreatitis, whereas phospholipids have a protective effect.

Intestinal over-expression of iron transporters induces iron overload in birds in captivity.

Hereditary hemochromatosis (HH) is a frequent genetic disease of older subjects of northern European descent. It is characterized by increased iron absorption and severe iron overloading in parenchymal organs. A similar disturbance of iron metabolism occurs in specific animal species in captivity. To address the key features leading to high absorption and thus to iron overload in these animals, we have studied the two iron transport proteins DMT1 and Ireg1 in the best-known susceptible species, the mynah bird. Here, we show that these birds have a high expression of DMT1 in the duodenum and also a strikingly high expression of Ireg1 along the whole small intestine. We believe that the iron accumulation in susceptible species only occurs in captivity because of a genotypic adaptation to their natural environment, where contrary to captivity, dietary iron is hardly available. The Caucasian population carrying mutations leading to iron overload today may have also benefited from the genetic advantage of up-regulating iron transport millennia ago, when dietary iron was scarce.

The mechanism of regression of solid SL2 lymphosarcoma after local IL-2 therapy.

Treatment of cancer by the administration of interleukin-2 (IL-2) at the tumour site is a very effective approach. The mechanism of this tumour regression is not clear, although it is generally assumed that it involves an IL-2-stimulated immune reaction. There are, however, no immune parameters that consistently correlate with the therapeutic effect. We have studied the histopathological events in a subcutaneously (s.c.) growing SL2 lymphosarcoma (transplantation of tumour cells at day 0) treated with peritumoural IL-2 injections at days 10-14. Most IL-2-treated tumours had already begun to regress from day 12 onwards, showing that local IL-2 therapy was also effective in the present study. The immediate reaction after local IL-2 administration is vascular leakage from the surrounding circulation, causing oedema within the tumour and in a broad zone surrounding it. The presence of oedema is always accompanied by markedly increased tumour necrosis. After a few days extensive angiogenesis occurs at the border between the oedematous area and the healthy connective tissue. Leucocytes, mainly macrophages, migrate via the newly formed blood vessels to gain access to the necrotising tumour site, where they form a granuloma. These macrophages phagocytose the dead tumour material. During growth, the SL-2 tumours infiltrate the surrounding tissue. The infiltrating tumour strands are apparently attacked by macrophages, as the tumour cells in close proximity to the latter are progressively destroyed. Therefore, the body of the tumour and the infiltrating tumour strands are attacked in different ways. The primary effect of IL-2 administration at the tumour site is vascular leakage that causes oedema in and around the tumour. This is followed by extensive angiogenesis, with the resulting migration of white cells from the circulation, which form a granuloma around the tumour. Both the oedema and the granuloma cause tumour regression.

Flagella-mediated bacterial motility accelerates but is not required for Salmonella serotype Enteritidis invasion of differentiated Caco-2 cells.

The relative contributions of the flagellum and the flagella-associated bacterial motility in the invasion of Caco-2 cells by Salmonella serotype Enteritidis were investigated using an fliC mutant defective in flagellin production and a motA mutant that carries flagella but is non-motile. Infection assays demonstrated that, at 1 h of infection, both the fliC and the motA mutants were severely impaired in bacterial invasion compared to the parental strain. Infection assays at 3 h infection demonstrated virtually equal invasion levels for both non-motile mutants and the parental strain. Together these data suggest that flagella-mediated bacterial motility accelerates the invasion of Salmonella but is not required for the invasion event per se.