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Characterization of group B streptococcal invasion in HEp-2 epithelial cells
P Valentin-Weigand1, H Jungnitz, A Zock
1Department of Microbiology, GBF-National Research Centre for Biotechnology, Braunschweig, Germany.
Abstract:
The invasion of group B streptococci (GBS) in HEp-2 epithelial cells was analyzed by electron microscopy and a quantitative antibiotic survival assay. Invasion of GBS involved intimate attachment of streptococcal chains, engulfment of the adherent bacteria by cellular protrusions, entry of the bacteria in a 'polar' fashion and formation of membrane-bound vacuoles in which most of the intracellular streptococci resided. At later stages of infection bacteria were also found free in the cytoplasm. Efficient uptake of streptococci by HEp-2 cells occurred within 20 min and live intracellular bacteria were detectable up to 48 h post-infection. Invasion of GBS required activation of the eukaryotic actin microfilament system involving, at least partially, protein kinase signal transduction pathways. Invasion was inhibited in a dose-dependent manner by decreasing extracellular Ca2+ levels as well as by substances known to interfere with eukaryotic calcium regulatory systems. These results suggest that GBS invade HEp-2 cells by triggering calcium-dependent phagocytosis-like internalization mechanisms and persist intracellularly both in vacuoles and free in the cytoplasm.
Insights
Group B Streptococcus (GBS) invades HEp-2 cells through a calcium-dependent phagocytosis-like process. These bacteria persist intracellularly within vacuoles and the cytoplasm for up to 48 hours.
Area of Science:
- Microbiology
- Cell Biology
- Infectious Diseases
Background:
- Group B Streptococcus (GBS) is a significant human pathogen.
- Understanding bacterial invasion mechanisms is crucial for developing effective treatments.
Purpose of the Study:
- To elucidate the mechanisms by which GBS invades HEp-2 epithelial cells.
- To identify host cell factors involved in GBS internalization and intracellular survival.
Main Methods:
- Electron microscopy to visualize bacterial-host cell interactions.
- Quantitative antibiotic survival assays to assess intracellular bacterial loads.
- Investigated the role of the actin cytoskeleton and calcium signaling.
Main Results:
- GBS invades HEp-2 cells via engulfment, forming membrane-bound vacuoles.
- Intracellular GBS are detectable up to 48 hours post-infection, residing in vacuoles and cytoplasm.
- Bacterial invasion depends on the host cell's actin microfilament system and calcium signaling.
- Invasion is inhibited by reduced extracellular calcium and interference with calcium regulatory systems.
Conclusions:
- GBS utilizes calcium-dependent, phagocytosis-like mechanisms for HEp-2 cell invasion.
- Intracellular persistence of GBS involves both vacuolar and cytoplasmic compartments.
- Host cell calcium regulation plays a critical role in GBS internalization.