title: Impact of vacuum cooling on Escherichia coli O157:H7 infiltration into lettuce tissue.
abstract: Vacuum cooling is a common practice in the California leafy green industry. This study addressed the impact of vacuum cooling on the infiltration of Escherichia coli O157:H7 into lettuce as part of the risk assessment responding to the E. coli O157:H7 outbreaks associated with leafy green produce from California. Vacuum cooling significantly increased the infiltration of E. coli O157:H7 into the lettuce tissue (2.65E+06 CFU/g) compared to the nonvacuumed condition (1.98E+05 CFU/g). A stringent surface sterilization and quadruple washing could not eliminate the internalized bacteria from lettuce. It appeared that vacuuming forcibly changed the structure of lettuce tissue such as the stomata, suggesting a possible mechanism of E. coli O157:H7 internalization. Vacuuming also caused a lower reduction rate of E. coli O157:H7 in stored lettuce leaves than that for the nonvacuumed condition.
authors.affiliation: Western Institute for Food Safety and Security, School of Veterinary Medicine, University of California Davis, Davis, California 95616, USA. hpli@ucdavis.edu
authors.forename: Haiping
authors.initials: H
authors.lastname: Li
authors.forename: Mehrdad
authors.initials: M
authors.lastname: Tajkarimi
authors.forename: Bennie I
authors.initials: BI
authors.lastname: Osburn
mesh_terms: D002140:California; D015169:Colony Count, Microbial; D019453:Escherichia coli O157 / Q000302:isolation & purification*; D005511:Food Handling / Q000379:methods*; D018545:Lactuca / Q000382:microbiology*; D050296:Microbial Viability; D014618:Vacuum