Fluorescence characterization of clinically-important bacteria

Healthcare-associated infections (HCAI/HAI) represent a substantial threat to patient health during hospitalization and incur billions of dollars additional cost for subsequent treatment. One promising method for the detection of bacterial contamination in a clinical setting before an HAI outbreak occurs is to exploit native fluorescence of cellular molecules for a hand-held, rapid-sweep surveillance instrument. Previous studies have shown fluorescence-based detection to be sensitive and effective for food-borne and environmental microorganisms, and even to be able to distinguish between cell types, but this powerful technique has not yet been deployed on the macroscale for the primary surveillance of contamination in healthcare facilities to prevent HAI. Here we report experimental data for the specification and design of such a fluorescence-based detection instrument. We have characterized the complete fluorescence response of eleven clinically-relevant bacteria by generating excitation-emission matrices (EEMs) over broad wavelength ranges. Furthermore, a number of surfaces and items of equipment commonly present on a ward, and potentially responsible for pathogen transfer, have been analyzed for potential issues of background fluorescence masking the signal from contaminant bacteria. These include bedside handrails, nurse call button, blood pressure cuff and ward computer keyboard, as well as disinfectant cleaning products and microfiber cloth. All examined bacterial strains exhibited a distinctive double-peak fluorescence feature associated with tryptophan with no other cellular fluorophore detected. Thus, this fluorescence survey found that an emission peak of 340nm, from an excitation source at 280nm, was the cellular fluorescence signal to target for detection of bacterial contamination. The majority of materials analysed offer a spectral window through which bacterial contamination could indeed be detected. A few instances were found of potential problems of background fluorescence masking that of bacteria, but in the case of the microfiber cleaning cloth, imaging techniques could morphologically distinguish between stray strands and bacterial contamination

Vortex dynamics and states of artificially layered superconducting films with correlated defects

Linear resistances and $IV$-characteristics have been measured over a wide range in the parameter space of the mixed phase of multilayered a-TaGe/Ge films. Three films with varying interlayer coupling and correlated defects oriented at an angle $\approx 25$ from the film normal were investigated. Experimental data were analyzed within vortex glass models and a second order phase transition from a resistive vortex liquid to a pinned glass phase. Various vortex phases including changes from three to two dimensional behavior depending on anisotropy have been identified. Careful analysis of $IV$-characteristics in the glass phases revealed a distinctive $T$ and $H$-dependence of the glass exponent $\mu$. The vortex dynamics in the Bose-glass phase does not follow the predicted behavior for excitations of vortex kinks or loops.Comment: 16 pages, 10 figures, 3 table

Antibiotic resistance determinants in the interplay between food and gut microbiota

A complex and heterogeneous microflora performs sugar and lactic acid fermentations in food products. Depending on the fermentable food matrix (dairy, meat, vegetable etc.) as well as on the species composition of the microbiota, specific combinations of molecules are produced that confer unique flavor, texture, and taste to each product. Bacterial populations within such “fermented food microbiota” are often of environmental origin, they persist alive in foods ready for consumption, eventually reaching the gastro-intestinal tract where they can interact with the resident gut microbiota of the host. Although this interaction is mostly of transient nature, it can greatly contribute to human health, as several species within the food microbiota also display probiotic properties. Such an interplay between food and gut microbiota underlines the importance of the microbiological quality of fermented foods, as the crowded environment of the gut is also an ideal site for genetic exchanges among bacteria. Selection and spreading of antibiotic resistance genes in foodborne bacteria has gained increasing interest in the past decade, especially in light of the potential transferability of antibiotic resistance determinants to opportunistic pathogens, natural inhabitants of the human gut but capable of acquiring virulence in immunocompromised individuals. This review aims at describing major findings and future prospects in the field, especially after the use of antibiotics as growth promoters was totally banned in Europe, with special emphasis on the application of genomic technologies to improve quality and safety of fermented foods

Characterization of a cold-active esterase from Lactobacillus plantarum suitable for food fermentations

Lactobacillus plantarum is a lactic acid bacteria that can be found in numerous fermented foods. Esterases from L. plantarum exert a fundamental role in food aroma. In the present study, the gene lp-2631 encoding a putative esterase was cloned and expressed in Escherichia coli BL21 (DE3) and the overproduced Lp-2631 protein has been biochemically characterized. Lp-2631 exhibited optimal esterase activity at 20 °C and more than 90% of maximal activity at 5 °C, being the first cold-active esterase described in a lactic acid bacteria. Lp-2631 exhibited 40% of its maximal activity after 2 h of incubation at 65 °C. Lp-2631 also showed marked activity in the presence of compounds commonly found in food fermentations, such as NaCl, ethanol, or lactic acid. The results suggest that Lp-2631 might be a useful esterase to be used in food fermentations. © 2014 American Chemical Society.This work was financially supported by grants AGL2011-22745 and BFU2010-17929 (MINECO), S2009/AGR-1469 (ALIBIRD) (Comunidad de Madrid), and RM2012-00004 (INIA). M. Esteban-Torres is a recipient of a JAE predoctoral fellowship from the CSIC.Peer Reviewe

Characterization of lactic acid bacteria isolated from wheat bran sourdough

U Dept. of Food, Environmental and Nutritional Science, University of Milan, Milan, Italy K University of Eastern Finland, Institute of Public Health and Clinical Nutrition, Kuopio, Finland U Institute of Sciences of Food Production, Italian National Research Council, Milan, Ital