MICROBIAL ECOLOGY AND SAFETY OF FRESH ON-FARM ORGANICALLY GROWN PRODUCE
Title: Use of bacteriophages in controlling E. coli in leafy vegetables
Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: July 14, 2010
Publication Date: August 22, 2010
Citation: Sharma, M. 2010. Use of bacteriophages in controlling E. coli in leafy vegetables. [abstract]. 17th Australian HACCP Conference.
Interpretive Summary: Bacteriophages are viruses which can infect and lyse (kill) bacteria. They are present throughout the environment and in various types of foods. Outbreaks of human illness associated with lettuce and spinach contaminated with Escherichia coli O157:H7. Bacteriophages specific for E. coli O157:H7 may provide a treatment to control the pathogens on leafy greens at refrigeration temperatures. When bacteriophages were sprayed on fresh cut lettuce inoculated with E. coli O157:H7, the bacteriophages were very effective in reducing the pathogens on lettuce. Bacteriophages killed E. coli O157:H7 very quickly on the surface of the lettuce. Other workers have shown the effectiveness of bacteriophages specific for E. coli O157:H7 on other leafy greens and produce commodities, indicating that bacteriophages may provide a safe effective treatment to control E. coli O157:H7 on fresh cut produce.
Bacteriophages are viruses that can infect and lys (kill) bacteria. These viruses are not harmful to humans and are present in the environment and many foods. Enterohemmorhagic E. coli (EHEC), like E. coli O157:H7, have been associated with contaminated bagged leafy green commodities. Outbreaks of foodborne illness have been associated with the consumption of cantaloupes and fresh-cut lettuce. Bacteriophage mixtures may be effective biocontrol agents to reduce E. coli O157:H7 on produce. The effectiveness of a mixture of bacteriophages (ECP-100) in reducing populations of E. coli O157:H7 on cut pieces of iceberg lettuce and cantaloupe was determined. E. coli O157:H7 gfp 86 was spot inoculated on lettuce pieces (9 cm2) with 3.76 log CFU/cm2, allowed to dry for 1 hr, and then sprayed with either control (phosphate buffered saline) or ECP-100 to deliver 7.98 log PFU/cm2 before being stored for either 0, 1, or 2 days at 4oC. Cut pieces of cantaloupe were spot inoculated with E. coli O157:H7 (4.55 log CFU/ml) and treated with control or ECP-100 (6.69 log PFU/ml), and then stored at 4 or 20oC for 0, 2, 5, or 7 days. On appropriate days, lettuce and cantaloupe samples were homogenized and populations of E. coli O157:H7 were enumerated on sorbitol MacConkey agar with ampicillin. Significant (P < 0.05) effect of phage treatment on bacterial populations was determined. Populations of E. coli O157:H7 on lettuce treated with ECP-100 on 0, 1, and 2 days (0.72, < 0.22, and 0.58 log CFU/cm2 of lettuce) and stored at 4oC were significantly lower than those treated with control (2.64, 1.79, and 2.22 log CFU/cm2), respectively. Populations on cut cantaloupes treated with ECP-100 on days 2, 5, and 7 (0.77, 1.28, and 0.96 log CFU/ml) and stored at 4oC were significantly lower than those treated with control (3.34, 3.23, and 4.09 log CFU/ml), respectively. The bacteriophage treatment reduced populations of E. coli O157:H7 immediately upon application to lettuce. This study is the first to shows the effectiveness of a bacteriophage mixture to kill E. coli O157:H7 on fresh-cut lettuce and cantaloupes. The work presented above, along with studies by other authors showing the effectiveness of the E. coli O157-specific and Salmonella-specific bacteriophages on various melons and other vegetables, shows that bacteriophages deserve attention for as a biocontrol agent for foodborne pathogens.