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ARS Home » Northeast Area » Beltsville, Maryland (BARC) » Beltsville Agricultural Research Center » Environmental Microbial & Food Safety Laboratory » Research » Publications at this Location » Publication #302502
Title: Effect of a bacteriophage cocktail in combination with modified atmosphere packaging in controlling Listeria monocytogenes on fresh-cut spinach

Author
item BOYACIOGLU, OLCAY - Adnan Mederes University
item SULAKVLEIDZE, ALEXANDER - Intralytix, Inc
item Sharma, Manan
item GOKTEPE, IPEK - Qatar University

Submitted to: Irish Journal of Agricultural Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/7/2016
Publication Date: N/A
Citation: N/A

Interpretive Summary: Listeria monocytogenes is a bacterial pathogen which has been associated with contaminated produce commodities like celery and cantaloupe, causing multiple deaths. Several fresh-cut leafy green products have been recalled due to the presence of L. monocytogenes. Bacteriophages are viruses specific for bacteria that have the ability infect and lyse (kill) their target bacteria without affecting other species. Previous research indicates that bacteriophages can be used to control pathogenic E. coli and Salmonella, suggesting that this approach could also be applicable to L. monocytogenes. In this experiment, several bacteriophages specific for L. monocytogenes were applied to inoculated fresh cut spinach, after which the spinach was stored under modified atmospheric packaging (MAP) and refrigeration for 14 days; these conditions mimic the current commercial packaging regime for fresh-cut, leafy greens. The bacteriophages specific for L. monocytogenes reduced the pathogen by 1.95 log CFU/cm2 on spinach under MAP conditions compared to controls which were not treated with bacteriophages. Under atmospheric conditions, the phage treatment reduced L. monocytogenes populations by 1.51 log CFU/cm2 compared to untreated phage controls. The results indicate that lytic bacteriophages specific for Listeria monocytogenes are effective in reducing the pathogen on packaged, fresh-cut spinach stored at 4oC. These results will be useful to other scientists and the leafy greens industry.

Technical Abstract: A Listeria monocytogenes-specific bacteriophage cocktail (ListShield™) was evaluated for its activity against a nalidixic acid-resistant L. monocytogenes (Lm-NalR) isolate on fresh-cut spinach stored under modified atmosphere packaging (MAP) at various temperatures. Pieces (~2x2 cm2) of fresh spinach inoculated with 4.5 log CFU cm-2 Lm-NalR were sprayed with ListShield™ (6.5 log PFU cm-2) or control. Samples were stored at 4 or 10°C for up to 14 days inside sealed packages filled with either a) ambient atmospheric air (AA) or b) modified atmosphere (MA) (5% O2/35% CO2/60% N2). At 4°C under AA, the phage cocktail significantly (P = 0.05) lowered the Lm-NalR populations on spinach by 1.12 and 1.51 log CFU cm-2 compared to control-treated inoculated spinach leaf pieces after 1 and 14 days, respectively. When stored under MA at 4°C, phages significantly reduced Lm-NalR populations on spinach by 1.95 log CFU cm-2 compared to the control-treated inoculated leaves after both 1 and 14 days. At 10°C, Lm-NalR populations on spinach after storage under AA were significantly reduced by 1.50 and 2.51 log CFU cm-2 by phage-treatment compared to control-treated inoculated spinach during 14 days storages, respectively. Again, significant reductions due to phage treatment under MA storage were measured as 1.71 and 3.24 log CFU cm-2 compared to control-treated inoculated leaves after 1 and 14 days of storage, respectively. The results of this study support the use of lytic bacteriophages in effectively reducing populations of potential L. monocytogenes contamination on fresh-cut leafy produce, under both atmospheric and MAP conditions.