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Uptake pathways of clinical isolates of Proteus mirabilis into human epithelial cell lines
1Department of Bacterial Diseases, Walter Reed Army Institute of Research, Washington, DC 20307-5100, USA.
Abstract:
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.
Insights
Proteus mirabilis bacteria efficiently invade human epithelial cells. Different bacterial isolates utilize distinct cellular mechanisms, involving microfilaments, microtubules, and endocytosis, for entry.
Area of Science:
- Microbiology
- Cell Biology
- Infectious Diseases
Background:
- Proteus mirabilis is a Gram-negative bacterium frequently associated with urinary tract infections.
- Understanding bacterial invasion mechanisms is crucial for developing effective therapeutic strategies.
Purpose of the Study:
- To investigate the invasion capabilities of Proteus mirabilis isolates into human epithelial cells.
- To elucidate the host cell mechanisms employed during P. mirabilis internalization.
Main Methods:
- Gentamicin protection assays were used to quantify bacterial invasion.
- Inhibition of host cell protein synthesis (cycloheximide) and bacterial macromolecular synthesis were assessed.
- Specific inhibitors targeted microfilaments, microtubules, and receptor-mediated endocytosis.
Main Results:
- Proteus mirabilis isolates demonstrated high invasion efficiencies into various epithelial cell lines.
- Bacterial macromolecular synthesis was essential for invasion, while host protein synthesis was not.
- Uptake mechanisms varied, involving microfilaments, microtubules, and endocytosis depending on the isolate and cell type.
Conclusions:
- Proteus mirabilis employs diverse eukaryotic cellular processes for internalization.
- Invasion mechanisms are adaptable and differ based on bacterial source and target epithelial cells.
- These findings highlight the complex host-pathogen interactions during P. mirabilis infections.