EXAMINATION OF ATTACHMENT AND PHAGOCYTIC UPTAKE OF LISTERIA SPECIES BY MAMMALIAN INTESTINAL-CELLS

Strains of Listeria monocytogenes, Listeria innocua, Listeria ivanovii, Listeria welshimeri and Listeria seeligeri isolated from diverse source were examined in an attempt to determine if their potential for attachment to intestinal epithelial cells and their behavior towards gut phagocytes was similar. Blood phagocytes were included for a comparison of their phagocytic activity with gut macrophages. Guinea pig small intestine was the source of intestinal epithelial cells and gut macrophages for the assays. Attachment of the bacteria to whole tissue was performed by incubation at 37°C of Listeria with small pieces of bowel, followed by staining and examination under light microscopy. Phagocytic cells were isolated from the gut by the use of EDTA, collagenase and DNAse, and peripheral blood cells were separated by differential centrifugation with Ficoll-Hypaque. Phagocytic activity was allowed to take place for 15 min at 37°C and the phagocytic index (PI) was determined from the number of ingested bacteria. Assays with gentamicin were included in order to assess the fate of ingested Listeria with respect to viability. Attachment of Listeria stains to the gut epithelial cells varied and could not be correlated either with the strain or with the source of the bacteria. The most significant differences in phagocytic activity were observed at the gut cell level. Overall, the PI was higher for L. monocytogenes than for L. innocua. A great variability occurred in the results and was due mostly to animal variation. © 1993 Academic Press Limited.