Escherichia coli K1 invasion of human brain microvascular endothelial cells

Involvement of Bacterial Extracellular Membrane Nanovesicles in Infectious Diseases and Their Application in Medicine

Bacterial extracellular membrane nanovesicles (EMNs) are attracting the attention of scientists more and more every year. These formations are involved in the pathogenesis of numerous diseases, among which, of course, the leading role is occupied by infectious diseases, the causative agents of which are a range of Gram-positive and Gram-negative bacteria. A separate field for the study of the role of EMN is cancer. Extracellular membrane nanovesicles nowadays have a practical application as vaccine carriers for immunization against many infectious diseases. At present, the most essential point is their role in stimulating immune response to bacterial infections and tumor cells. The possibility of nanovesicles' practical use in several disease treatments is being evaluated. In our review, we listed diseases, focusing on their multitude and diversity, for which EMNs are essential, and also considered in detail the possibilities of using EMNs in the therapy and prevention of various pathologies.

Colistin kills bacteria by targeting lipopolysaccharide in the cytoplasmic membrane

Colistin is an antibiotic of last resort, but has poor efficacy and resistance is a growing problem. Whilst it is well established that colistin disrupts the bacterial outer membrane (OM) by selectively targeting lipopolysaccharide (LPS), it was unclear how this led to bacterial killing. We discovered that MCR-1 mediated colistin resistance in Escherichia coli is due to modified LPS at the cytoplasmic rather than OM. In doing so, we also demonstrated that colistin exerts bactericidal activity by targeting LPS in the cytoplasmic membrane (CM). We then exploited this information to devise a new therapeutic approach. Using the LPS transport inhibitor murepavadin, we were able to cause LPS accumulation in the CM of Pseudomonas aeruginosa, which resulted in increased susceptibility to colistin in vitro and improved treatment efficacy in vivo. These findings reveal new insight into the mechanism by which colistin kills bacteria, providing the foundations for novel approaches to enhance therapeutic outcomes.

Transcellular traversal of the blood-brain barrier by the pathogenic Propionibacterium acnes

BACKGROUND

Propionibacterium acnes (P. acnes) is an anaerobe commonly stay in the body as part of the commensal microbiota, and a dominant bacterium of the human skin and hair follicles. It has been found that this bacterium could participate in brain inflammation that causes Alzheimer's disease (AD) and Parkinson's disease (PD). But how P. acnes invade the brain remains elusive.

METHODS

We established the in vitro blood-brain barrier (BBB) model by culturing the HBMEC/D3 cell line on collagen-coated PFTE membrane. The BBB model was verified by the transepithelial electrical resistance (TEER) and horseradish peroxidase (HRP) permeability rate, and observed by the scanning electron microscope (SEM), transmission electron microscope (TEM), as well as confocal microscope. The P. acnes was then cocultured with the in vitro BBB model and the permeability of P. acnes was measured by counting the bacteria clones collected from the lower chamber of the model.

RESULTS

High local concentration of P. acnes invaded the in vitro BBB model through the transcellular traversal pathway. The permeability for P. acnes was increased by the treatment of lipopolysaccharide (LPS), but not mannitol. P. acnes invasion elevated the expression of cell adhesion molecules E-selectin, ICAM-1, and VCAM-1 in HBMEC cells.

CONCLUSION

P. acnes has the ability to penetrate the brain though transcellular invasion of the blood-brain barrier.

Escherichia coli K1 utilizes host macropinocytic pathways for invasion of brain microvascular endothelial cells

Eukaryotic cells utilize multiple endocytic pathways for specific uptake of ligands or molecules, and these pathways are commonly hijacked by pathogens to enable host cell invasion. Escherichia coli K1, a pathogenic bacterium that causes neonatal meningitis, invades the endothelium of the blood-brain barrier, but the entry route remains unclear. Here, we demonstrate that the bacteria trigger an actin-mediated uptake route, stimulating fluid phase uptake, membrane ruffling and macropinocytosis. The route of uptake requires intact lipid rafts as shown by cholesterol depletion. Using a variety of perturbants we demonstrate that small Rho GTPases and their downstream effectors have a significant effect on bacterial invasion. Furthermore, clathrin-mediated endocytosis appears to play an indirect role in E. coli K1 uptake. The data suggest that the bacteria effect a complex interplay between the Rho GTPases to increase their chances of uptake by macropinocytosis into human brain microvascular endothelial cells.

Fluorescent labeling of cranberry proanthocyanidins with 5-([4,6-dichlorotriazin-2-yl]amino)fluorescein (DTAF)

A novel methodology was developed to elucidate proanthocyanidins (PAC) interaction with extra-intestinal pathogenic Escherichia coli (ExPEC). PAC inhibit ExPEC invasion of epithelial cells and, therefore, may prevent transient gut colonization, conferring protection against subsequent extra-intestinal infections, such as urinary tract infections. Until now PAC have not been chemically labeled with fluorophores. In this work, cranberry PAC were labeled with 5-([4,6-dichlorotriazin-2-yl]amino) fluorescein (DTAF), detected by high-performance liquid chromatography with diode-array detection and characterized by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS). We report single and double fluorescent-labeled PAC with one or two chlorine atoms displaced from DTAF in alkaline pH via nucleophilic substitution. Fluorescent labeling was confirmed by fragmentation experiments using MALDI-TOF/TOF MS. Fluorescent labeled PAC were able to promote ExPEC agglutination when observed with fluorescence microscopy. DTAF tagged PAC may be used to trace the fate of PAC after they agglutinate ExPEC and follow PAC-ExPEC complexes in cell culture assays.