Antimicrobial Effects of Sodium Metasilicate AgainstListeria monocytogenes

Abstract

Sodium metasilicate (SMS) is a U.S. Department of Agriculture-approved antimicrobial for use in meat and poultry processing and has been known to be effective against various foodborne pathogens. However, its antimicrobial mechanism has not yet been revealed. In this study, we attempted to elucidate the mechanism by which SMS inactivates Listeria monocytogenes, a Gram-positive bacterial pathogen encountered commonly in ready-to-eat meat and poultry products. L. monocytogenes (Scott A) cells were treated with different concentrations of SMS (1.0, 2.0, 3.0, 4.0, 5.0, and 6.0% [wt/vol]) and compared with high pH treatment (0.1, 0.2, and 0.3N NaOH solutions) for 1, 10, and 30 min. SMS exhibited concentration and time effects on inactivation of L. monocytogenes. The effect of SMS on the membrane integrity and viability of L. monocytogenes was determined by use of propidium iodide (PI) and SYTO9 nucleic acid stains with subsequent flow cytometry. The breakage in membrane integrity was observed by uptake of PI by cells treated with SMS with subsequent flow cytometry. Ultrastructural changes from corresponding transmission electron micrographs further revealed the disruption in the cytoplasmic membrane and changes in the morphology of the cells treated with SMS and high pH. The results from flow cytometry experiment and transmission electron microscopy study indicated that following SMS treatment, the membrane integrity of L. monocytogenes was compromised leading to leakage of intracellular contents and subsequent cell death.

Mechanism of Antimicrobial Action of Sodium Metasilicate AgainstSalmonella entericaserovar Typhimurium

“…The most possible explanation could be the quenching effect or the fluorescence energy transfer when SYTO9 and PI dyes were used in combination (Stocks, 2004;Berney et al, 2007). A similar effect was observed in our previous study, when L. monocytogenes suspensions were treated with SMS and stained with PI and SYTO9 (Sharma et al, 2012b). Percentage of PI stained cells following 30-min treatment with 0.1 N NaOH was much lower than with 30-min treatment to any concentration of SMS (Fig.…”

“…In a similar study, exposure of E. coli O157:H7 to 0.6% SMS (pH 12.1), resulted in 100% inhibition with no recoverable E. coli O157:H7 (Weber et al, 2004). Higher concentrations of SMS were needed (up to 4%) to completely inactivate L. monocytogenes following 30 min in vitro treatment (Sharma et al, 2012b) as compared to 0.5% needed to inactivate Salmonella observed in this study. These findings indicate that Gram-negative pathogens such as Salmonella are more susceptible to SMS as compared to Gram-positive L. monocytogenes, which possess a thicker peptidoglycan layer that provides protection against harsh alkaline conditions (Mendonca et al, 1994).…”

“…Being a highly alkaline chemical, it is corrosive to skin, and proper care should be followed before using this chemical. The use of SMS as an antimicrobial has shown efficacy against Salmonella, Escherichia coli O157:H7 and Listeria monocytogenes in vitro and in meat systems (Weber et al, 2004;Carlson et al, 2008;Pohlman et al, 2009;Sharma et al, 2012aSharma et al, , 2012b. Sodium metasilicate had no antimicrobial effect against Salmonella on chicken breast fillets when the high pH of SMS was neutralized (unpublished data).…”

“…The objectives of the present study were to determine the in vitro antimicrobial efficacy of SMS against Salmonella enterica serovar Typhimurium and to elucidate its mechanism of antimicrobial action. The combination of flow cytometry with fluorescent nucleic acid stains (such as propidium iodide [PI]) has been used to assess a variety of cell functions including cell viability and other physiological functions in both Gram-negative and Gram-positive pathogens (Gruden et al, 2004;Paparella et al, 2008;Kim et al, 2009;Sharma et al, 2012b). In the present study, a combination of PI and SYTO9 dyes was used with flow cytometry to assess the changes in membrane integrity of Salmonella Typhimurium treated with SMS and high pH.…”

Inhibitory effect of nerol against Aspergillus niger on grapes through a membrane lesion mechanism

“…PI, a membrane impermeable dye, binds with double-stranded nucleic acids with a stoichiometry of one dye molecule per four to five base pairs of DNA in order to produce red fluorescent signals (Sharma, Williams, Schneider, Schmidt, & Rodrick, 2012). An obvious improvement in spore size (FSC) and generally smaller changes in complexity (SSC) was observed after exposure to 12 h of incubation (Fig.…”