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.