title: Survival and recovery of Escherichia coli O157:H7, Salmonella, and Listeria monocytogenes on lettuce and parsley as affected by method of inoculation, time between inoculation and analysis, and treatment with chlorinated water.
abstract: The effects of method for applying inoculum and of drying time after inoculation on survival and recovery of foodborne pathogens on iceberg lettuce and parsley were studied. Five-strain mixtures of Escherichia coli O157:H7, Salmonella, or Listeria monocytogenes were applied to lettuce and parsley by dip, spot, or spray inoculation methods. Inocula were dried for 2 h at 22 degrees C or for 2 h at 22 degrees C and then 22 h at 4 degrees C before being treated with water (control) or chlorine (200 microg/ml). Significantly higher populations (CFU per lettuce or parsley sample) of E. coli O157:H7 and Salmonella (alpha = 0.05) were recovered from dip-inoculated produce than from spot- or spray-inoculated produce. This difference was attributed to larger numbers of cells adhering to lettuce and parsley subjected to dip inoculation. Populations of E. coli O157:H7 and Salmonella recovered from lettuce inoculated by spot and spray methods were not significantly different, but populations recovered from spot-inoculated parsley were significantly higher than those recovered from spray-inoculated parsley, even though the number of cells applied was the same. Significantly different numbers of L. monocytogenes were recovered from inoculated lettuce (dip > spray > spot); populations recovered from dip-inoculated parsley were significantly higher than those recovered from spot- or spray-inoculated parsley, which were not significantly different from each other. Populations of pathogens recovered from lettuce and parsley after drying inoculum for 2 h at 22 degrees C were significantly higher than or equal to populations recovered after drying for 2 h at 22 degrees C and then for 22 h at 4 degrees C. Significant differences (water > chlorine) were observed in populations of all pathogens recovered from treated lettuce and parsley, regardless of inoculation method and drying time. It is recommended that spot inoculation with a drying time of 2 h at 22 degrees C followed by 22 h at 4 degrees C be used to determine the efficacy of chlorine and other sanitizers in killing foodborne pathogens on lettuce and parsley.
authors.affiliation: Center for Food Safety and Department of Food Science and Technology, University of Georgia, 1109 Experiment Street, Griffin, Georgia 30223-1797, USA.
authors.forename: Megan M
authors.initials: MM
authors.lastname: Lang
authors.forename: Linda J
authors.initials: LJ
authors.lastname: Harris
authors.forename: Larry R
authors.initials: LR
authors.lastname: Beuchat
mesh_terms: D001422:Bacterial Adhesion; D002713:Chlorine / Q000494:pharmacology*; D015169:Colony Count, Microbial; D004202:Disinfectants / Q000494:pharmacology*; D019453:Escherichia coli O157 / Q000187:drug effects / Q000254:growth & development* / Q000502:physiology; D005511:Food Handling / Q000379:methods; D005516:Food Microbiology; D018545:Lactuca / Q000382:microbiology*; D008089:Listeria monocytogenes / Q000187:drug effects / Q000254:growth & development* / Q000502:physiology; D028528:Petroselinum / Q000382:microbiology*; D012475:Salmonella / Q000187:drug effects / Q000254:growth & development* / Q000502:physiology; D013696:Temperature; D013997:Time Factors
chemical_list: D004202:Disinfectants; D002713:Chlorine