Antimicrobial Effects of Sodium Metasilicate AgainstListeria monocytogenes

Effects of phosphate and silicate on stiffness and viscoelasticity of mature biofilms developed with simulated drinking water

Biofilms, a porous matrix of cells aggregated with extracellular polymeric substances under the influence of chemical constituents in the feed water, can develop a viscoelastic response to mechanical stresses. In this study, the roles of phosphate and silicate, common additives in corrosion control and meat processing, on the stiffness, viscoelasticity, porous structure networks, and chemical properties of biofilm were investigated. Three-year biofilms on PVC coupons were grown from sand-filtered groundwater with or without one of the non-nutrient (silicate) or nutrient additives (phosphate or phosphate blends). Compared with non-nutrient additives, the phosphate and phosphate-blend additives led to a biofilm with the lowest stiffness, most viscoelastic, and more porous structure, including more connecting throats with greater equivalent radii. The phosphate-based additives also led to more organic species in the biofilm matrix than the silicate additive did. This work demonstrated that nutrient additives could promote biomass accumulation but also reduce mechanical stability.

Mechanism of antimicrobial action of sodium metasilicate against Salmonella enterica serovar Typhimurium

Sodium metasilicate (SMS) is an alkaline antimicrobial approved by the U.S. Department of Agriculture for use in poultry processing and ready-to-eat poultry products. The objectives of this study were to determine the effectiveness of SMS against Salmonella enterica serovar Typhimurium in suspension and to elucidate the antimicrobial mechanism of action of SMS. Salmonella Typhimurium (ATCC 14028) was exposed to 0 (positive control), 0.5%, 1%, 2% (wt/vol) SMS and 0.1 N NaOH (high pH) solutions for 1, 10, and 30 min. The viability of Salmonella Typhimurium cells treated with different SMS concentrations and high pH was determined on selective and nonselective media and by staining with fluorescent propidium iodide (PI) and SYTO9 nucleic acid stains in combination with flow cytometry. Transmission electron microscopy of Salmonella Typhimurium cells was performed to observe the changes at the cellular level following exposure to SMS and high pH treatments. Treating Salmonella Typhimurium cells with SMS (as low as 0.5%) resulted in immediate inactivation of Salmonella with no detectable survivors. The breakage in membrane integrity and loss of cell viability was observed by PI uptake by cells treated with SMS with subsequent flow cytometry. Salmonella Typhimurium cells exposed to SMS and high pH appeared wrinkled, vacuolated, and lysed with their cytoplasmic material leaking into extracellular matrix on transmission electron micrographs. The findings from this study indicate that SMS acts on the cytoplasmic membrane and causes lysis of the cells and leakage of intracellular contents.