A novel, time-effective approach for capturing bacteria from contaminated urine samples.

BACKGROUND: A fundamental step in the race to design a rapid diagnostic test for antimicrobial resistance is the separation of bacteria from their matrix. Many recent studies have been focused on the development of systems capable of separating and capturing bacteria from liquid environments. METHODS: Herein, we introduce a new approach to this issue by using the natural bacteria tendency to accumulate at naturally-occurring interfaces, such as liquid-gas and liquid-solid interfaces, where also organic molecules like lipids, proteins, and polysaccharides accumulate. This bacterial behavior leads to the formation of a superficial layer close to the interface rich in bacteria, from which it is possible to capture a consistent amount of bacteria by means of surfaces with high chemical affinity to the outer bacteria surface. RESULTS: This paper demonstrates how to capture bacteria from contaminated urine samples, by means of commercial microscope slides coated with positively charged biomolecules, without the utilization of the bacterial culture step for multiplying the bacteria. CONCLUSIONS: This approach is an easy, quick and economical method to concentrate living bacteria in a well-defined position onto a microscope slide, thus making them easily available for further diagnostic investigations.

Size effects in nanoindentation of hard and soft surfaces.

Nanoindentation experiments carried out with atomic force microscopes (AFMs) open the way to understand size-related mechanical effects that are not present at the macro- or micro-scale. Several issues, currently the subject of a wide and open debate, must be carefully considered in order to measure quantities and retrieve trends genuinely associated with the material behaviour. The shape of the nanoindenter (the AFM tip) is crucial for a correct data analysis; we have recently developed a simple geometrical model to properly describe the tip effect in the nanoindentation process. Here, we demonstrate that this model is valid in indentation of both soft and hard, or relatively hard, materials carried out by two distinct, commercially available, AFM probes. Moreover, we implement the model with a data interpretation approach aimed at preventing underestimation of the tip penetration into the material. Experiments on soft polymeric materials (poly(methyl methacrylate) and polystyrene) and hard or relatively hard (Si, Au, Al) materials are reported. The results demonstrate that true hardness data can be attained also in shallow indentations and that the appearance of size effects strongly depends on data interpretation issues. In addition, we report on stiffness data measured on the considered materials during their nanoindentation.

AFM characterization of rabbit spermatozoa.

Atomic force microscopy (AFM) has been applied for determining the topological and structural features of rabbit spermatozoa. Fresh ejaculated spermatozoa were adsorbed passively onto a silicon slide or by motility from suspension onto a poly(L-lysine)-coated glass coverslip and then imaged in air and in buffer saline, respectively. AFM images clearly highlighted many details of spermatozoa head, neck, and tail. Distinct features were observed in the plasmatic membrane of spermatozoa. In particular, head topography easily recognized the acrosome, equatorial segment, equatorial subsegment, and postacrosome regions. Moreover, AFM images revealed the presence of double belt of invaginations around the spermatozoa head, at the boundary between equatorial subsegment and postacrosome regions. All together, the collected AFM images clearly defined a detailed map of spermatozoa morphology while giving some hints on the internal structure.

An atomic force microscopy tip model for investigating the mechanical properties of materials at the nanoscale.

Investigation of the mechanical properties of materials at the nanoscale is often performed by atomic force microscopy nanoindentation. However, substrates with large surface roughness and heterogeneity demand careful data analysis. This requirement is even more stringent when surface indentations with a typical depth of a few nanometers are produced to test material hardness. Accordingly, we developed a geometrical model of the nanoindenter, which was first validated by measurements on a reference gold sample. Then we used this technique to investigate the mechanical properties of a coating layer made of Balinit C, a commercially available alloy with superior anti-wear features deposited on steel. The reported results support the feasibility of reliable hardness measurements with truly nanosized indents.

Klebsiella pneumoniae antibiotic resistance identified by atomic force microscopy.

In the last decade the detection of the resistance of bacteria to antibiotics treatment, developed by different kind of bacteria, is becoming a huge problem. We hereby present a different approach to the current problem of detection of bacteria resistance to antibiotics. Our aims were to use the atomic force microscopy (AFM) to investigate bacteria morphological changes in response to antibiotics treatment and explore the possibility of reducing the time required to obtain information on their resistance. In particular, we studied Klebsiella pneumoniae bacteria provided by the Lavagna Hospital ASL4 Liguria (Italy), where there are cases linked with antibiotics resistance of the Klebsiella pneumoniae. By comparing AFM images of bacteria strains treated with different antibiotics is possible to identify unambiguously the Klebsiella pneumoniae strains resistant to antibiotics. In fact, the analysis of the AFM images of the antibiotic-sensitive bacteria shows clearly the presence of morphological alterations in the cell wall. While in the case of the antibiotic-resistant bacteria morphological alterations are not present. This approach is based on an easy and potentially rapid AFM analysis.

Solid state NMR investigation of the molecular dynamics of cocoon silks produced by different Bombyx mori (Lepidoptera) strains.

Cocoons produced by different strains of Bombyx mori larvae were investigated by a combination of several high- and low-resolution 1H and 13C solid-state NMR techniques in order to characterize and compare their dynamic behavior at a molecular level. A detailed interpretation in terms of molecular motions in these very complex systems was possible thanks to the integrated analysis of different relaxation measurements and high-resolution selective experiments. Untreated cocoons of all strains were found to be mainly constituted by two different types of rigid domains and by a third one, more mobile, due to physisorbed water molecules. Dynamic processes in the MHz and kHz ranges were characterized by means of different 1H and 13C relaxation times. Cocoons arising from different strains exhibit a different content of physisorbed water and also slightly different dynamic behavior, especially in the MHz regime.