TITLE:
Antimicrobial Effects of Plant Compounds against Virulent Escherichia coli O157:H7 Strains Containing Shiga Toxin Genes in Laboratory Media and on Romaine Lettuce and Spinach
AUTHORS:
Javier R. Reyna-Granados, Lynn A. Joens, Bibiana Law, Mendel Friedman, Sadhana Ravishankar
KEYWORDS:
E. coli O157:H7, Shiga Toxin Genes, Romaine Lettuce, Spinach, Inactivation, Essential Oils, Plant Extracts
JOURNAL NAME:
Food and Nutrition Sciences,
Vol.12 No.4,
April
22,
2021
ABSTRACT: Escherichia coli strains produce Shiga-toxins Stx-1 and Stx-2 that contribute to their
virulence. The objective was to evaluate antimicrobial activities of plant
essential oils (oregano, cinnamon, lemongrass), their active components (carvacrol,
cinnamaldehyde, citral) and plant-extracts (green tea polyphenols, apple skin,
black tea, decaffeinated black tea, grapeseed and pomace extracts) against E. coli O157:H7 strains containing Stx-1 and Stx-2 genes, as determined by Multiplex Polymerase Chain Reaction, in vitro and on leafy greens. Antimicrobials at various concentrations in sterile
PBS were added to bacterial cultures (~3 - 4 logs
CFU/ml), mixed thoroughly, and incubated at 37°C. Surviving bacteria were enumerated at 0, 1,
3, 5 and 24 h. The most effective essential oil (oregano oil; 0.5%) and plant
extract (green tea; 3%) were evaluated against E. coli O157:H7 on romaine lettuce and spinach stored at 4°C for 7 days. Microbial survival was a
function of the concentration of antimicrobials and incubation times. All
antimicrobials reduced bacterial population to below detection levels in vitro; however, essential oils and active components exhibited greater
activity than plant extracts. Oregano oil and green tea reduced E. coli O157:H7 on lettuce and spinach to below detection. Plant-based
antimicrobials have the potential to protect foods against E. coli O157: