Salmonella | EPFL Graph Search

Salmonella (en français les Salmonelles) est un genre de bacilles Gram négatifs (BGN) de la famille des Enterobacteriaceae. Son nom fait référence au vétérinaire Daniel E. Salmon. Certains sérovars de certaines sous-espèces de Salmonella enterica sont responsables d'infections bactériémiques graves, les fièvres typhoïde et paratyphoïdes, qui sévissent surtout dans les pays en développement. D'autres sérovars sont impliqués dans des gastro-entérites et des toxi-infections alimentaires (TIAC) plus bénignes. Taxonomie Le genre Salmonella est créé en 1900 par Joseph Léon Lignières pour recevoir une espèce impliquée dans des bactériémies porcines accompagnées de lésions hémorragiques. Jusqu'en 2016 il était rattaché par des critères phénotypiques à la famille des Enterobacteriaceae. Malgré la refonte de l'ordre des Enterobacterales par Adeolu en 2016 à l'aide des techniques de phylogénétique moléculaire, Salmonella reste dans la famille des Entero

Preparation and Analysis of Bacteria Surface-Modified with Polymer Nanoparticles

Lisa Patricia Elisabeth Bader

Cell-based drug carriers present an interesting approach to improve the targeted delivery of therapeutic drugs in vivo. Specifically, bacterial cells possess interesting properties such as motility and sensing that allow some strains to selectively target tumor areas. Immobilization of abiotic materials on the cell surface of such bacterial cells can therefore enable the delivery of therapeutic compounds at the desired location. The work presented in this thesis explores the fabrication and characterization of bacteria-nanoparticle biohybrids as potential carriers for drug delivery applications.Chapter 1 presents a review of the scientific literature that covers the different approaches to immobilize abiotic materials on the surface of bacteria. It highlights the advantages of using cells as carriers for the transport of therapeutics. An effective drug delivery agent should present great motility, viability, biodistribution and biocompatibility with human cells. Examples of various chemical approaches to surface-modify bacteria are presented. Chapter 2 systematically explores the immobilization of polystyrene nanoparticles on the surface of Escherichia coli (E. coli) and Salmonella typhimurium (Salmonella) cells. We compared the nanoparticle immobilization using four different conjugations strategies (electrostatic, covalent and ligand-ligand) and characterized the bio-hybrids systems using flow cytometry and confocal microscopy. Two different microscopy techniques were used: the first was based on 3D-reconstruction of z-stacks of single bacterium to investigate position of nanoparticles on the membrane; the second allowed for a large screening of bacteria followed by image processing determining the area of bacteria covered by nanoparticles. We observed that the efficiency of the surface modification is correlated to the initial nanoparticle/cell ratio and that non-covalent strategies allowed for increased number of biohybrids formed and nanoparticle attached. This study provides an overview of the variety of conjugation strategies (and their conjugation efficiencies) available for fabricating nanoparticle-decorated bacteria and presents us an opportunity to better understand and design bacteria-based target-specific drug delivery systems.Chapter 3 presents the characterization of the previously developed bacteria-nanoparticle biohybrids as potential carriers for nanoparticle transport. The viability of the various conjugates was determined by flow cytometry indicating a decrease in cell viability with increasing numbers of nanoparticles immobilized on the membrane. The motility was studied to investigate the impact of nanoparticle attachment on the bacterial velocity as well as the capacity to transport the cargo. Bacteria were able to transport nanoparticles when prepared with low ratios of nanoparticle/cell.

EPFL2022

Inactivation by solar photo-Fenton in pet bottles of wild enteric bacteria of natural well water: Absence of re-growth after one week of subsequent storage

Juliette Ndounla, César Pulgarin

Iron photo-assisted inactivation of wild enteric bacteria (total coliforms/E. coil and Salmonella spp.) was carried out in water from the Sahelian wells having different pH (W1:4.9 and W2: 6.3) and a natural iron content of 0.07 mg/L We evaluate the efficiency of the disinfection on different systems containing both or only one Fenton reagent (H2O2/Fe-2.): (i) H2O2/Fe2+/hv, (ii) Fe2+/hv, (iii) H2O2/hv, and (iv) only light irradiation (hv) at lab and field scale. Generally, 0.6 mg/L of Fe2+ and/or 8.5 mg/L of H2O2 were used in the Fenton reagent. The systems H2O2/Fe2+/hv and H2O2/hv led to total inactivation of Salmonella and E. coil. The natural iron content (0.07 mg/L) was enough to drive an efficient photo-Fenton process leading to total bacterial inactivation. Our results show that: (i) the iron salt present in Sahelian water is enough to perform a photo-Fenton disinfection of drinking water when adding H2O2, (ii) addition of external iron salts at near neutral pH has no additional effect on the bacterial photo-Fenton inactivation process. After one week of storage, no enteric bacteria re-growth was observed in treated waters. Mechanistic suggestions are presented to explain the observed results. (C) 2012 Elsevier B.V. All rights reserved.

Elsevier2013

Relevant impact of irradiance (vs. dose) and evolution of pH and mineral nitrogen compounds during natural water disinfection by photo-Fenton in a solar CPC reactor

Juliette Ndounla, César Pulgarin

The inactivation of total coliforms/E. coli (10(4) CFU/mL) and Salmonella spp. (10(5) CFU/mL) in well water naturally containing dissolved (Fe2+/3+) and solid iron forms (e.g. iron oxides) was carried out by photo Fenton treatment (Fe-2+,Fe-3+/H2O2/hv). In a preliminary run under simulated solar radiation, beyond 4 mg/L of added H2O2, the enteric bacteria were totally inactivated after 90 min. Thereafter, 25 L of well water were treated in the compound parabolic collector (CPC) under direct solar radiation. Three irradiation periods (i) 8 am to 2 pm (8-14h), (ii) 10 am to 4 pm (10-16 h) and (iii) 12 pm to 6 pm (12-18 h) were evaluated for assessing the impact of different solar irradiances (W m(-2)) on the enteric bacterial inactivation rates. Both studied strains were totally inactivated under sole exposure to solar radiation in the CPC when the experiments were conducted from 8 to 14h or 10 to 16 h. However, Salmonella spp. strains regrowth was noticed after the 24 h dark storage in all the samples previously treated with bare solar radiation. As the treated water contained Fe, the photo-Fenton disinfection at field scale in the CPC was carried out with the addition of H2O2 (10 mg/L). Significant enhancement of the enteric bacteria inactivation rate was therefore recorded comparatively to the one obtained under bare solar treatment. No regrowth was observed in water treated by photo-Fenton disinfection one week after the treatment. The comparative evaluation of photo-Fenton disinfection rate as a function of different irradiation periods was based on the monitoring of the effective disinfection time (EDT), or required time to acquire the total inactivation of targeted bacteria in defined conditions. Therefore, significant impact of the irradiance on the process was noticed. High average irradiance (Al) of 35W m(-2) led to the total inactivation of Salmonella spp. in an EDT of 45 min and a dose of 26 Wh m(-2); while low irradiance of 20W m(-2) required-an-EDT of 180 min for a-dose-60 Wh m(-2). Thus, the experiments revealed that lower irradiance level leads to higher doses to achieve the bacterial disinfection. pH, as well as nitrite and nitrate concentration, increased during the photo-disinfection processes, while depletion was recorded for aqueous ammonia concentration. (c) 2013 Published by Elsevier B.V.

Elsevier2014

Preparation and Analysis of Bacteria Surface-Modified with Polymer Nanoparticles

Lisa Patricia Elisabeth Bader

EPFL2022

Relevant impact of irradiance (vs. dose) and evolution of pH and mineral nitrogen compounds during natural water disinfection by photo-Fenton in a solar CPC reactor

Juliette Ndounla, César Pulgarin

Elsevier2014