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.

Antimicrobial effects of sodium metasilicate against Listeria monocytogenes.

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.

Ice immersion as a postharvest treatment of oysters for the reduction of Vibrio vulnificus.

Vibrio vulnificus produces serious illnesses that are commonly associated with shellfish consumption, particularly raw oysters. Ingestion can result in fatal septicemia in susceptible individuals with hepatitis, cirrhosis, immune dysfunction, diabetes, or hemochromatosis (metabolic iron overload). Therefore, postharvest treatments to reduce vibrio levels in oysters have been recommended. In this study, rapid chilling by immersion of unwashed whole oysters in ice for 3 h was assessed as a postharvest treatment for reduction of V. vulnificus. Treated oysters were subsequently refrigerated at 45 degrees F (7.2 degrees C), whereas control oysters were not iced but were maintained at 45 degrees F throughout the study. Homogenized meats were monitored for total heterotrophic aerobic bacteria, V. vulnificus, and fecal coliform content before and after treatment over a 2-week period. V. vulnificus was enumerated by DNA probe hybridization of colonies from standard plate counts on nonselective medium, and recovery was compared for several media. Loss of plating efficiency was observed on standard selective and differential media compared with nonselective agars. Numbers of V. vulnificus generally declined in treated samples compared with controls; however, increases in total heterotrophic bacteria and fecal coliforms were also observed in treated samples at some time points. This study does not support the use of ice immersion as a postharvest method because of the relatively small declines in V. vulnificus numbers and the possibility of concomitant increases in fecal coliform and total bacterial contamination.

Integrity of powdered and powder-free latex examination gloves.

OBJECTIVES: The difference in permeability between one brand of powdered and another of powder-free latex examination gloves was evaluated to determine leak rates. METHODS: Thirty-one of each type of glove were tested for each of three different conditions: usage by dental personnel (1) for 15 minutes or longer, (2) for less than 15 minutes, and (3) directly from the manufacturer's packaging (zero usage time). Each glove was evaluated in the fingers and the palm. The phiX-174 viral solution in the glove was allowed to penetrate for 15 minutes. Powder (cornstarch) was subsequently added to 20 powder-free gloves, and 15 of these were pierced with a 30-gauge needle. RESULTS: Powdered gloves showed no leakage rates. Because of this, 30-, 27-, and 25-gauge needles were used to pierce five gloves each. One glove with 27- and 25-gauge needle holes showed leakage. Leakage rates for powder-free gloves: 45.1 percent for more than 15 minutes of use, 25.8 percent for less than 15 minutes of use, and 16.1 percent for zero minutes of use. Two of the 20 pierced and one of the five unpierced powder-free gloves with added cornstarch leaked. CONCLUSION: Significant differences in leak results between powdered and powder-free gloves suggest further study is needed.