Uptake pathways of clinical isolates of Proteus mirabilis into human epithelial cell lines.

Proteus mirabilis isolates obtained from urine and faeces showed high invasion levels into several human epithelial cell lines in gentamicin assays. Invasion efficiencies of isolate 102 from a monkey with diarrhoea equalled or even exceeded those of Salmonella typhi strain Ty2 (6.3 to 13.8% of the inoculum). Vegetative, non-swarming P.mirabilis invaded epithelial cells efficiently and were found in endosomes and free in the cytoplasm. Although inhibition of eukaryotic protein synthesis by cycloheximide did not reduce bacterial uptake, inhibition with bacteriostatic antibiotics of bacterial protein-, RNA-, or DNA-synthesis reduced invasion drastically. Involvement of eukaryotic structures and processes in internalization was determined by using various inhibitors in the invasion assay. Uptake of P.mirabilis isolated from urine into gut (INT 407, HCT-8) cells and bladder (T24) cells was dramatically inhibited only by microfilament depolymerization. Internalization of faecal isolate 102 into gut or bladder epithelial cells was inhibited by depolymerization of microfilaments or microtubules. Engulfment of isolate 102 into T24 bladder cells was also reduced by inhibition of receptor-mediated endocytosis. Interference with endosome acidification decreased the number of intracellular bacteria of isolate 102 in all three cell lines. These results suggest that P.mirabilis isolates from different sources are internalized by epithelial cells by different eukaryotic processes, and that these processes can vary between cell lines.