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

• Published in: Journal of food protection Vol. 67; no. 6; pp. 1092 - 1103
• Main Authors: Lang, M.M, Harris, L.J, Beuchat, L.R
• Format: Journal Article
• Language: English
• Published: Des Moines, IA International Association of Milk, Food and Environmental Sanitarians 01.06.2004
• Subjects: antibacterial properties; Bacterial Adhesion; bacterial contamination; Biological and medical sciences; Chlorine - pharmacology; chlorine efficacy; Colony Count, Microbial; decontamination; dipping; Disinfectants - pharmacology; drying; Escherichia coli; Escherichia coli O157 - drug effects; Escherichia coli O157 - growth & development; Escherichia coli O157 - physiology; Escherichia coli O157:H7; food contamination; Food Handling - methods; Food industries; Food Microbiology; food pathogens; Fundamental and applied biological sciences. Psychology; General aspects; head lettuce; Hygiene and safety; inoculation methods; inoculum density; inoculum drying time; isolation; Lactuca - microbiology; Lactuca sativa var. capitata; Listeria monocytogenes; Listeria monocytogenes - drug effects; Listeria monocytogenes - growth & development; Listeria monocytogenes - physiology; parsley; pathogen survival; Petroselinum - microbiology; Petroselinum crispum; potassium phosphates; Salmonella; Salmonella - drug effects; Salmonella - growth & development; Salmonella - physiology; sanitation standard operating procedures; sanitizing; sodium hypochlorite; solutions; spot method; spraying; surface area; Temperature; Time Factors; washing; water; Salmonella; Vegetables; Chlorine; Escherichia coli; Petroselinum crispum; Listeria monocytogenes; Method; Survival; Inoculation; Lettuce; Decontamination; Dicotyledones; Angiospermae; Bacteria; Spermatophyta; Parsley; Umbelliferae; Enterobacteriaceae
• ISSN: 0362-028X; 1944-9097
• DOI: 10.4315/0362-028X-67.6.1092

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°C or for 2 h at 22°C and then 22 h at 4°C before being treated with water (control) or chlorine (200 microgram/ml). Significantly higher populations (CFU per lettuce or parsley sample) of E. coli O157:H7 and Salmonella (α = 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°C were significantly higher than or equal to populations recovered after drying for 2 h at 22°C and then for 22 h at 4°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°C followed by 22 h at 4°C be used to determine the efficacy of chlorine and other sanitizers in killing foodborne pathogens on lettuce and parsley.