Purpose: The objective was to compare the antimicrobial activities of the following plant extracts against E. coli O157:H7 in laboratory media: apple polyphenol; black, decaffeinated black and green tea extracts; and grapeseed extract.
Methods: Four concentrations of dehydrated powders (4%, 3%, 2% and 1%) were each dissolved or suspended in sterile phosphate-buffered saline solution. These solutions/suspensions were then added to the test bacterial cultures (103-4 CFU/µl), mixed thoroughly, and incubated at 37 °C for various time periods. Aliquots taken at five time periods (0, 1, 3, 5 and 24 hours) were then enumerated for surviving bacterial populations.
Results: All plant extracts exhibited strong concentration- and time-dependent in vitro antimicrobial activity against E. coli O157:H7. Green tea at ≥ 2% reduced the bacterial population below detection (3-4 logs) after 1 h, and after 3 hours at a concentration of 1%. Grapeseed extract (1-4%) at 3 h induced reduction of the pathogen below detection limits. Apple polyphenol at 1-2% reduced pathogen population to below detection levels at 3 h; at 4% induced 2.5-log reduction at 1 hr; and at 2-3 % reduced bacterial population to below detection at 5 h. Black tea at ≤ 2% produced ~3 log reduction in 3 h. Decaffeinated black tea induced a 2-log reduction at 3 h and complete reduction at 24 h.
Significance: This research provides potential antimicrobial candidates against E. coli O157:H7 in various milieus, including human food and animal feed formulations.