ARS | Publication request: The use of lytic bacteriophages to reduce E. coli O157:H7 on fresh cut lettuce introduced through cross-contamination

Submitted to: Bacteriophage
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: March 15, 2013
Publication Date: N/A

Interpretive Summary: Lytic bacteriophages (phages), viruses which have the ability to kill pathogenic foodborne bacteria, were evaluated for their ability to prevent contamination of fresh cut lettuce. Lettuce was first treated with the phages and then exposed to E. coli O157:H7, an enteric foodborne pathogen which has contaminated various produce commodities (lettuce, spinach, sprouts, hazelnuts) in recent years. Lettuce was either sprayed with the phages or immersed in a phage solution, and then stored for a period of time at low temperature (refrigeration). The results presented here indicate that the manner and amount of phages applied to the lettuce influenced the extent to which E. coli O157:H7 populations were reduced on the fresh cut lettuce surface. This work provides a preliminary indication that exposure of lettuce to lytic bacteriophages may reduce E. coli O157:H7 populations on fresh cut lettuce stored at refrigerated temperatures. This information should be useful to other scientists and the fresh produce industry.

Technical Abstract: The role of lytic bacteriophages in preventing cross contamination of produce has not been evaluated. A cocktail of three lytic phages specific for E. coli O157:H7 (EcoShield) at 108 PFU/ml or a control (phosphate buffered saline, PBS) was applied to lettuce by either 1) spraying on to lettuce pieces (9 cm2) before inoculation with E. coli O157:H7; 2) immersion of lettuce in Ecoshield for 30 s or 2 min before introduction of E. coli O157:H7to lettuce; 3) the spray-application of Ecoshield to lettuce inoculated with E. coli O157:H7 following exposure to 50 'g/ml chlorine for 30 s. For spray studies, lettuce pieces (9 cm2) were sprayed with 5.98 log PFU/cm2 and then were spot inoculated with 2.38 log CFU/cm2 E. coli O157:H7. For immersion studies, lettuce was immersed in either 500 ml of 108 PFU/ml Ecoshield or PBS for 30 s and 2 min, and then spot-inoculated with E. coli O157:H7 (50 'l at 5.1 log CFU/ml) E. coli O157:H7. Phage-treated, inoculated lettuce pieces were stored at 4oC for and analyzed for E. coli O157:H7 populations for up to 7 days. Spraying phages on to cut lettuce reduced E. coli O157:H7 compared to control (PBS) treatments, but no statistical differences (p > 0.05) were observed . The method of application affected the ability of EcoShield to reduce E. coli O157:H7 populations on fresh cut lettuce.