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In recent years, a dramatic increase in incidence of the dextro-rotatory tartrate-positive variant (dT+) of Salmonella enterica subspecies enterica serovar Paratyphi B has been observed in poultry and poultry products. In the present study the interactions of this bacterium with the host were studied in vivo and in vitro in an attempt to explain the preferential association of this serotype with poultry. The ability of this organism to invade and multiply in chicken intestinal epithelial cells and the intracellular behaviour in chicken macrophages was studied in vitro using chicken cell lines. In vivo challenge experiments in specific pathogen-free chickens were carried out to determine the level of colonization of caeca and internal organs early after experimental infection. An in vivo trial with commercial broiler chickens, using a seeder model, was performed to determine whether S. Paratyphi B dT+ could persist and spread in broilers until slaughter. S. Paratyphi B dT+ invaded and multiplied in the chicken epithelial cell line and survived in a chicken macrophage cell line. The strain used colonized caeca and internal organs of chickens to a high extent 1 week after infection with a low-dose inoculum. Moreover, the strain was efficiently transmitted within a group of broilers and persisted until slaughter. It was concluded that S. Paratyphi B dT+ was well adapted to poultry and therefore it is suggested that specific control measures against this serotype should be considered.

Salmonella infections in reptiles, in contrast to those in birds and mammals, are limited to the intestinal tract. In this study, interactions of a strain of Salmonella enterica subsp. enterica serovar Muenchen (SEEM) with intestinal explants of the turtle Trachemys scripta scripta were examined by scanning electron microscopy (SEM). Adhesion and invasion in the chelonian intestinal explants at 30°C and 37°C were evaluated quantitatively. For purposes of comparison, the invasive capacity of SEEM in the continuous avian epithelial cell line DIV-1 at 30°C and 37°C was determined. Small numbers of M-like cells were found in the ileum of the turtles. The bacteria adhered mainly to the mucus of the intestinal explants. Only small numbers of salmonellae were associated with epithelial cells. Higher numbers of bacteria adhered at 30°C than at 37°C. Epithelial damage, embedding of bacteria in the epithelial surface and a ruffling-like process were noted only at 37°C. Minimal numbers of salmonellae invaded the explants at 30°C and 37°C. Invasion of DIV-1 cells was greater at 37°C than at 30°C. The study suggested that the intestinal mucous layer provides an important site of colonization for salmonellae in the chelonian host and protects the underlying epithelial cells.

Temperature of culture can be used to modulate cellular metabolism for improving small intestinal cell culture and cryopreservation. An hypothermia pretreatment (2 days at 25°C and 3 hours recovery at 37°C) improved hamster cell survival to freeze-thaw damage (p < 0.01) but decreased the survival of 2 immortal pig ileal cell lines even though epithelioid IPI-2I cells were more tolerant to hypothermia than IPI-I fibroblasts. Epithelioid cells survived 3 days at 25°C with unaltered expression of cytokeratin-18 whereas colonies of fibroblasts did not survive more than a day at 25°C (p < 0.001). These results suggest that hypothermia-tolerance of pig ileal cell lines might differ according to cell lineage calling for further experiments on small intestinal primary cell culture. Copyright 1994, 1999 Academic Press

Summary The assay of reverse transcriptase (RT) activity was used to detect the presence of retrovirus in porcine cells. A set of optimal assay conditions was determined to design a sensitive, quantitative and reproducible RT assay for porcine systems. The template-primer poly(rA).oligo(dT) was an absolute requirement. The presence of Mn++ was indispensable, with an optimal concentration of 0.25 mM. Monocations (K+, Na+) at 50 mM greatly enhanced, but their high doses inhibited the reaction. The pH of the medium influenced very much the reaction, especially with non-purified virus samples, with which the RT activity was inhibited at pHs above 8.2. Non-ionic detergents at 1% enhanced several-fold the RT activity. It was also shown that porcine retrovirus could be spontaneously reactivated in porcine cell lines by in vitro long-term propagation and transmitted to pigs by inoculation with virus-producing cells.

The internalization of Listeria by intestinal epithelial cells is still poorly understood, however it is becoming apparent that microorganisms have developed the ability to interact with host cell receptor molecules to induce their own internalization. In this report we show that inhibition of cell tyrosine phosphorylation by protein tyrosine kinase (PTK) inhibitors blocks L. monocytogenes entry into both finite and immortalized intestinal cell lines. Some differences were observed between the Listeria species. L. monocytogenes entry was inhibited by between 10- to 100-fold by PTK inhibitors competing with the tyrosine residue binding of the kinase as erbstatin or by PTK inhibitors competing with the binding of ATP to the enzyme as genistein and some tyrphostins. On the other hand, L. ivanovii entry was inhibited by erbstatin as observed with L. monocytogenes but poorly by genistein and tyrphostins. The use of these several PTK inhibitors shows that even though both L. monocytogenes and L. ivanovii entered intestinal and other call lines by stimulating PTK, it seems that L. monocytogenes stimulated a different PTK than L. ivanovii. According to the fact that the number of PTK receptors increases on immortalized cells, the higher L. monocytogenes internalization observed with immortalized cell lines could be related to a higher PTK receptor number on these calls compared to finite cell lines, Copyright 1994, 1999 Academic Press