Confocal spectral microscopy, a non-destructive approach to follow contamination and biofilm formation of mCherry Staphylococcus aureus on solid surfaces

Evaluation of Salmonella biofilm attachment and hydrophobicity characteristics on food contact surfaces

Salmonella forms biofilms, and persist on food contact surfaces. Once a biofilm is formed cleaning and sanitation protocols may be inadequate for effective removal. This study evaluated attachment characteristics, surface properties, and structure of Salmonella biofilms on food contact surfaces commonly used in the tree-fruit industry. Multi-strain Salmonella biofilms were grown in a Centers for Disease Control and Prevention (CDC) biofilm reactor at 22 ± 2 °C and sampling was conducted at 2, 24 and 96-h. After each incubation period, coupons weregently rinsed and the remaining cells enumerated. Biofilms were analyzed with Laser Scanning Confocal Microscopy (LSCM). Hydrophobicity was evaluated by measuring the contact angles of reference liquids method using a drop tensiometer instrument. Material type and biofilm age significantly influenced attachment and biofilm hydrophobicity (P < 0.05). The strength of attachment, across all time points, was highest on nylon followed by wood and high-density polyethylene. The highest contact angle measurements were observed after 96-h of biofilm formation for each material. All the results and observations from this study contribute to a better understanding of the attachment and hydrophobicity characteristics of Salmonella and might help producers make informed decisions when selecting containers for harvesting and storing in order to minimize biofilm formation and potential for cross-contamination.

Antibacterial Activity of Zinc-Doped Hydroxyapatite and Vancomycin-Loaded Gelatin Nanoparticles against Intracellular Staphylococcus aureus in Human THP-1 Derived Macrophages

Treating bone infections with common antibiotics is challenging, since pathogens like Staphylococcus aureus can reside inside macrophages. To target these intracellular bacteria, we have proposed nanoparticles (NPs) as drug carriers. This study aims to investigate the efficacy of hydroxyapatite and gelatin NPs, selected in view of their bone mimicry and potential for targeted delivery, as carriers for the antibacterial agents zinc and vancomycin. Therefore, two distinct NPs are fabricated: zinc-doped hydroxyapatite (ZnHA) and vancomycin-loaded gelatin (VGel) NPs. The NPs are characterized based on morphology, size, chemical composition, cellular internalization, and intracellular bactericidal efficacy. Specifically, the intracellular bactericidal efficacy is tested using a validated coculture model of human THP-1 derived macrophages and phagocytosed S. aureus bacteria. Scanning electron microscopy (SEM) and Fourier transform-infrared spectroscopy (FTIR) results show that the spherical NPs are synthesized successfully. These NPs are internalized by THP-1 cells and show >75% colocalization with lysosomes without compromising the viability of the THP-1 cells. Both ZnHA and VGel NPs substantially reduce the intracellular survival of S. aureus compared to the direct addition of dissolved zinc and vancomycin. Concluding, our NPs are highly effective drug delivery vehicles to kill intracellular S. aureus, which stress the potential of these NPs for future clinical translation.

The survival of multi-drug resistant bacteria on raw Douglas fir material

In today's age of ecological transition, the use of materials such as renewable wood in construction is particularly relevant, but also a challenge in the healthcare sector where the hygiene dimension also comes into play. In this study we have investigated the survival of multi-resistant bacteria commonly responsible for healthcare-associated infections (HAIs) (ESBL-positive Klebsiella pneumoniae and glycopeptide-resistant Enterococcus faecalis) on two different types of wood (Douglas fir : Pseudotsuga menziesii and Maritime Pine : Pinus pinaster) compared to other materials (smooth: stainless steel and rough: pumice stone) and the effect of a disinfection protocol on the bacterial survival on Pseudotsuga menziesii. Approximately 108 bacteria were inoculated on each material and bacterial survival was observed over several days (D0, D1, D2, D3, D6, D7 and D15). Each analysis was performed in triplicate for each time and material. The results show an important reduction of the bacterial inoculum for Klebsiella pneumoniae and Enterococcus faecalis on Douglas fir, in contrast with the results obtained on maritime pine, stainless steel and pumice stone. No bacterial survival was detected on Douglas fir after application of a hospital disinfection protocol. These different results show that wood may have a place in the future of healthcare construction. Further studies would be interesting to better understand the different properties of wood.

Bloch Surface Waves Mediated Micro-Spectroscopy

Micro-spectroscopy is a critical instrument for spectrum analysis in various applications such as chemical and biological analysis, environment detection, and hyperspectral imaging. However, current micro-spectral technique requires bulky and costly spectrometer. In this report, a new type of Bloch surface wave (BSW) based micro-spectrometer is proposed. A single silicon nanoparticle sitting on a dielectric multilayer substrate is used to excite the BSW which acts as a nanoscale unknown source. Taking advantage of the dispersion relations of BSWs, an abundant spectrally related database is formed that is useful for spectrum retrieval applications. Back-focal plane images are used to monitor the change of angular spectrum corresponding to the dispersion relationship of Bloch surface waves. Combined with an iterative algorithm, experimental retrieval of visible-range monochromatic and broadband light spectrums can be obtained. The resolution of the spectrometers can reach 2 nm across a wavelength range of 130 nm. The method in this work is CMOS compatible, enabling spectra retrieval for nanoscale radiators and can also be used to measure and retrieve the microscopic spectrum signal rapidly and timely without conventional scanning monochromator spectrometer.