Membrane damages in bacteria interacting with silica nanoparticles revealed by AFM

International audienceNanoparticles (NPs) can interact with biological systems, with either negative or positive consequences (potential risks or elimination of pathogenic bacteria). In this context, we investigate the morphology and physico-chemical properties of Escherichia coli bacteria interacting with silica NPs by Atomic Force Microscopy (AFM), this method providing access to topographic information and local rheological properties at the nm scale (with a discrimination between “hard”, NPs, and “soft”, bacteria, materials), either in air or physiological environment. AFM images show that silica NPs tend to aggregate around bacteria, their further action depending on their diameter. The presence of big NPs (100 and 200 nm) does not change E. coli morphology, bacteria remaining rod-shaped and high. The bacterial external membrane keeps also its organization in domains, suggesting that such NPs are too voluminous to penetrate into bacteria. On the contrary, in the presence of small NPs (4 and 10 nm) bacteria adopt unusual spherical shapes, some of them even suffering from a partial collapse, leading to the release of cellular compounds. The external membrane is also disturbed, exhibiting spherical aggregates, which could be due to a reorganization of lipopolysaccharides present in this membrane

Amperometric Polyphenol Biosensor Based on Tyrosinase Immobilization on CoAl Layered Double Hydroxide Thins Films

International audienceAn amperometric biosensor based on tyrosinase immobilized on the sensor surface has been used for the detection of polyphenols extracted from green tea. The immobilization was ensured by the crosslinking method on thins films of CoAlSO 4 layered double hydroxide recovering screen-printed gold electrodes. Electrochemical measurements show that this biosensor is able to detect tea polyphenols by following the reduction of compounds enzymatically generated. Its response is linear in the concentration range of [0-2,4 µM] with high sensitivity and stability, since it retains 90% of its original response after 20 days

Membrane damages in bacteria interacting with silica nanoparticles revealed by AFM

Nanoparticles (NPs) can interact with biological systems, with either negative or positive consequences (potential risks or elimination of pathogenic bacteria). In this context, we investigate the morphology and physico-chemical properties of Escherichia coli bacteria interacting with silica NPs by Atomic Force Microscopy (AFM), this method providing access to topographic information and local rheological properties at the nm scale (with a discrimination between “hard”, NPs, and “soft”, bacteria, materials), either in air or physiological environment. AFM images show that silica NPs tend to aggregate around bacteria, their further action depending on their diameter. The presence of big NPs (100 and 200 nm) does not change E. coli morphology, bacteria remaining rod-shaped and high. The bacterial external membrane keeps also its organization in domains, suggesting that such NPs are too voluminous to penetrate into bacteria. On the contrary, in the presence of small NPs (4 and 10 nm) bacteria adopt unusual spherical shapes, some of them even suffering from a partial collapse, leading to the release of cellular compounds. The external membrane is also disturbed, exhibiting spherical aggregates, which could be due to a reorganization of lipopolysaccharides present in this membrane

Staphylococcus aureus binds to the N-terminal region of corneodesmosin to adhere to the stratum corneum in atopic dermatitis.

Staphylococcus aureus colonizes the skin of the majority of patients with atopic dermatitis (AD), and its presence increases disease severity. Adhesion of S. aureus to corneocytes in the stratum corneum is a key initial event in colonization, but the bacterial and host factors contributing to this process have not been defined. Here, we show that S. aureus interacts with the host protein corneodesmosin. Corneodesmosin is aberrantly displayed on the tips of villus-like projections that occur on the surface of AD corneocytes as a result of low levels of skin humectants known as natural moisturizing factor (NMF). An S. aureus mutant deficient in fibronectin binding protein B (FnBPB) and clumping factor B (ClfB) did not bind to corneodesmosin in vitro. Using surface plasmon resonance, we found that FnBPB and ClfB proteins bound with similar affinities. The S. aureus binding site was localized to the N-terminal glycine-serine-rich region of corneodesmosin. Atomic force microscopy showed that the N-terminal region was present on corneocytes containing low levels of NMF and that blocking it with an antibody inhibited binding of individual S. aureus cells to corneocytes. Finally, we found that S. aureus mutants deficient in FnBPB or ClfB have a reduced ability to adhere to low-NMF corneocytes from patients. In summary, we show that FnBPB and ClfB interact with the accessible N-terminal region of corneodesmosin on AD corneocytes, allowing S. aureus to take advantage of the aberrant display of corneodesmosin that accompanies low NMF in AD. This interaction facilitates the characteristic strong binding of S. aureus to AD corneocytes

Revisiting of the physico-chemical properties of polyelectrolyte multilayers for a fine tuning of the immobilization of bacteria or nanoparticles

Increasingly used in industrial coatings, polyelectrolytes multilayers (PEMs) are self-assembled systems made of the alternate deposition of oppositely charged polymers on substrates, usually built by the traditional layer-by-layer method. Their properties strongly depend on environmental physico-chemical parameters. Due to the variety of conditions used in the literature on the one hand and the diversity of polyelectrolytes systems on the other hand, it remains difficult to bring out general principles, leading now to a lack of a real understanding of the PEM buildup, from the macro- to the nanoscale. Here, combining acoustic and electrochemical methods with atomic force microscopy, in a systematic approach, we uncover the critical role of the deposition protocol in the growth regime of PEMs made of cationic poly (allylamine hydrochloride) and anionic poly(4-styrene sulfonate, sodium). Traditional dipping leads to thick, heterogeneous and relatively isolating PEMs whereas a spin-coating assisted method leads to thinner, homogeneous and more permeable PEMs. We also highlight that the pH and the ionic strength influence not only the electrostatic interactions and polyelectrolyte conformation in solution but also their organization after their adsorption on the substrate. Finally, our easily and rapidly adaptable protocol paves the way for promising potential bio-applications, since PEMs are applied to the bacterial immobilization on substrates or as a coating for nanostructured biosensor transducer.Immunocapteur à ondes de Love ultra-sensible pour la détection rapide de micro-organismes dans l'eau, visant la réalisation d'un dispositif d'alert