title: Fate of Shigella sonnei on parsley and methods of disinfection.
abstract: Outbreaks of shigellosis associated with chopped parsley used as a garnish for foods occurred in four states in the United States and in two Canadian provinces in 1998. This prompted a study to determine survival and growth characteristics of Shigella sonnei inoculated onto raw parsley. Two inoculum levels (approximately 10(3) and 10(6) CFU/g) were applied to parsley leaves, portions of which were then chopped. Inoculated whole and chopped parsley leaves were held at 4 degrees C or 21 degrees C for up to 14 days. Initial populations of the organism on chopped parsley receiving high or low levels of inoculum increased by approximately 3 log10 CFU/g, within 1 day at 21 degrees C. Populations of S. sonnei on inoculated chopped or whole parsley leaves held at 4 degrees C decreased by 2.5 to 3.0 log10 CFU/g during a 14-day storage period. The pathogen multiplied, without a lag phase, on inoculated (2.72 log10 CFU/g) chopped parsley held at 21 degrees C, exceeding 6 log10 CFU/g within 24 h. Treatment of inoculated whole parsley leaves with vinegar containing 5.2% (vol/vol) acetic acid or 200 ppm free chlorine for 5 min at 21 degrees C reduced the population of S. sonnei by more than 6 log10 CFU/g, whereas treatment with vinegar containing 7.6% acetic acid or 250 ppm free chlorine reduced initial populations of 7.07 and 7.26 log10 CFU/g, respectively, to undetectable levels (<0.6 log10 CFU/g). These studies revealed that S. sonnei can grow rapidly on chopped parsley held at ambient temperature and remain viable for at least 14 days at 4 degrees C. Treatment of contaminated parsley with vinegar or chlorinated water offers a simple method to reduce markedly or eliminate the pathogen in food-service or home settings.
authors.affiliation: Center for Food Safety and Quality Enhancement, University of Georgia, Griffin 30223-1797, USA.
authors.forename: F M
authors.initials: FM
authors.lastname: Wu
authors.forename: M P
authors.initials: MP
authors.lastname: Doyle
authors.forename: L R
authors.initials: LR
authors.lastname: Beuchat
authors.forename: J G
authors.initials: JG
authors.lastname: Wells
authors.forename: E D
authors.initials: ED
authors.lastname: Mintz
authors.forename: B
authors.initials: B
authors.lastname: Swaminathan
mesh_terms: D019342:Acetic Acid; D019661:Apiaceae / Q000382:microbiology*; D002713:Chlorine; D005516:Food Microbiology; D005519:Food Preservation / Q000379:methods*; D018515:Plant Leaves / Q000382:microbiology; D012764:Shigella sonnei / Q000302:isolation & purification*
chemical_list: D002713:Chlorine; D019342:Acetic Acid