3.2. Effect of ListShield™ on experimentally contaminated frozen
food entrees
Prepackaged frozen meals are often subject to a variety of
storage conditions in processing facilities, such as freezing, refrigerated
and ambient temperatures, before they are frozen for shipment
and long-term storage. To examine the effect of freezing and
thawing, frozen entrees (beef with potatoes, broccoli and tomato
sauce) were thawed, experimentally contaminated with
L. monocytogenes and treated with ListShield™ a rate of
1 107 PFU/g of meal for 30 min. These entrees were frozen then
thawed, for 24 h each. Subsequent enumeration of L. monocytogenes
showed a statistically significant reduction (p < 0.001) of
L. monocytogenes by over 99% in the ListShield™ treated samples
compared to the PBS treated control samples (Fig. 1C). While
freezing has been shown to reduce the levels of L. monocytogenes in
various foods, regrowth of the pathogen can occur once the foods
are thawed. In that context, our data suggest that application of
bacteriophages may further reduce the levels of L. monocytogenes in
foods frequently subjected to varying storage conditions, increasing
their safety during periods of prolonged storage at temperatures
that promote L. monocytogenes growth.
3.2. Effect of ListShield™ on experimentally contaminated frozenfood entreesPrepackaged frozen meals are often subject to a variety ofstorage conditions in processing facilities, such as freezing, refrigeratedand ambient temperatures, before they are frozen for shipmentand long-term storage. To examine the effect of freezing andthawing, frozen entrees (beef with potatoes, broccoli and tomatosauce) were thawed, experimentally contaminated withL. monocytogenes and treated with ListShield™ a rate of1 107 PFU/g of meal for 30 min. These entrees were frozen thenthawed, for 24 h each. Subsequent enumeration of L. monocytogenesshowed a statistically significant reduction (p < 0.001) ofL. monocytogenes by over 99% in the ListShield™ treated samplescompared to the PBS treated control samples (Fig. 1C). Whilefreezing has been shown to reduce the levels of L. monocytogenes invarious foods, regrowth of the pathogen can occur once the foodsare thawed. In that context, our data suggest that application ofbacteriophages may further reduce the levels of L. monocytogenes infoods frequently subjected to varying storage conditions, increasingtheir safety during periods of prolonged storage at temperaturesthat promote L. monocytogenes growth.
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