Conditions for Elimination of Escherichia Coli O157

Conditions for elimination of Escherichia coli O157:H7 on alfalfa seeds through a combination of high hydrostatic pressure and mild heat

Applied and environmental microbiology. 01/03/200903/2009;

Hudaa Neetoo, Thompson Pizzolato, Haiqiang Chen


Escherichia coli O157:H7 have been associated with contaminated seed sprout outbreaks. The majority of these outbreaks have been traced to sprout seeds contaminated with low levels of pathogens. Sanitizing sprout seeds presents a unique challenge in the arena of produce safety in that even a low residual pathogen population remaining on contaminated seed after treatments appears capable of growing to very high levels during sprouting. In this study, the effectiveness of high pressure treatment in combination with low and elevated temperatures was assessed for its ability to eliminate E. coli O157:H7 on artificially contaminated alfalfa seeds. Inoculated seed samples were treated at 600 MPa for 2 min at 4, 20, 25, 30, 35, 40, 45 and 50 degrees C. The pressure-sensitivity of the pathogenic bacteria was strongly dependent on the treatment temperature. At 40 degrees C, the process was adequate in eliminating a 5 log population on the seeds with no adverse effect on the seed viability. Treatments carried out at reduced pressure levels and/or extended treatment time, 550 MPa for 2 min at 40 degrees C, 300 MPa for 2 min at 50 degrees C, and 400 MPa for 5 min at 45 degrees C were equally lethal to the pathogen. When all the three treatments were compared in terms of their impact on the seed viability, the process of 550 MPa for 2 min at 40 degrees C was the most desirable achieving final germination percentages and sprout sizes statistically similar to control untreated seeds (P > 0.05).